permissions: 0.801
performance: 0.698
debug: 0.698
device: 0.603
semantic: 0.601
PID: 0.587
other: 0.568
network: 0.557
graphic: 0.555
files: 0.545
vnc: 0.528
socket: 0.528
boot: 0.514
KVM: 0.464

gcc 8.2 reports stringop-truncation when building qemu

QEMU 3.0

block/sheepdog.c: In function 'find_vdi_name':
block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
     strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


If this is the intended behavior, please suppress the warning. For example:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstringop-truncation"
    strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
#pragma GCC diagnostic pop

On Tue, Dec 18, 2018 at 3:09 PM Philippe Mathieu-Daudé
<email address hidden> wrote:
>
> GCC 8 added a -Wstringop-truncation warning:
>
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
>
> This new warning leads to compilation failures:
>
>     CC      migration/global_state.o
>   qemu/migration/global_state.c: In function 'global_state_store_running':
>   qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
>        strncpy((char *)global_state.runstate, state, sizeof(global_state.runstate));
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
>
> The runstate name doesn't require the strings to be NUL-terminated,
> therefore strncpy is the right function to use here.
>
> We could add a #pragma GCC diagnostic ignored "-Wstringop-truncation"
> around, disable the warning globally using -Wno-stringop-truncation,
> but since QEMU provides the strpadcpy() which does the same purpose,
> simply use it to avoid the annoying warning.
>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>

Reviewed-by: Marc-André Lureau <email address hidden>

> ---
>  migration/global_state.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 8e8ab5c51e..c7e7618118 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -42,8 +42,8 @@ int global_state_store(void)
>  void global_state_store_running(void)
>  {
>      const char *state = RunState_str(RUN_STATE_RUNNING);
> -    strncpy((char *)global_state.runstate,
> -           state, sizeof(global_state.runstate));
> +    strpadcpy((char *)global_state.runstate,
> +              sizeof(global_state.runstate), state, '\0');
>  }
>
>  bool global_state_received(void)
> --
> 2.17.2
>
>


-- 
Marc-André Lureau


On Tue, 18 Dec 2018 12:03:31 +0100
Philippe Mathieu-Daudé <email address hidden> wrote:

> From: Marc-André Lureau <email address hidden>
> 
> GCC 8 added a -Wstringop-truncation warning:
> 
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
> 
> This new warning leads to compilation failures:
> 
>     CC      hw/acpi/core.o
>   In function 'acpi_table_install', inlined from 'acpi_table_add' at qemu/hw/acpi/core.c:296:5:
>   qemu/hw/acpi/core.c:184:9: error: 'strncpy' specified bound 4 equals destination size [-Werror=stringop-truncation]
>            strncpy(ext_hdr->sig, hdrs->sig, sizeof ext_hdr->sig);
>            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   make: *** [qemu/rules.mak:69: hw/acpi/core.o] Error 1
> 
> The ACPI tables don't require the strings to be NUL-terminated,
> therefore strncpy is the right function to use here.
> 
> We could add a #pragma GCC diagnostic ignored "-Wstringop-truncation"
> around, disable the warning globally using -Wno-stringop-truncation,
> but since QEMU provides the strpadcpy() which does the same purpose,
> simply use it to avoid the annoying warning.
> 
> Signed-off-by: Marc-André Lureau <email address hidden>
> Reviewed-by: Eric Blake <email address hidden>
> Reviewed-by: Philippe Mathieu-Daudé <email address hidden>
> [PMD: reword commit subject and description]
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>

Reviewed-by: Igor Mammedov <email address hidden>

> ---
>  hw/acpi/aml-build.c |  6 ++++--
>  hw/acpi/core.c      | 13 +++++++------
>  2 files changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
> index 1e43cd736d..397833462a 100644
> --- a/hw/acpi/aml-build.c
> +++ b/hw/acpi/aml-build.c
> @@ -24,6 +24,7 @@
>  #include "hw/acpi/aml-build.h"
>  #include "qemu/bswap.h"
>  #include "qemu/bitops.h"
> +#include "qemu/cutils.h"
>  #include "sysemu/numa.h"
>  
>  static GArray *build_alloc_array(void)
> @@ -1532,13 +1533,14 @@ build_header(BIOSLinker *linker, GArray *table_data,
>      h->revision = rev;
>  
>      if (oem_id) {
> -        strncpy((char *)h->oem_id, oem_id, sizeof h->oem_id);
> +        strpadcpy((char *)h->oem_id, sizeof h->oem_id, oem_id, '\0');
>      } else {
>          memcpy(h->oem_id, ACPI_BUILD_APPNAME6, 6);
>      }
>  
>      if (oem_table_id) {
> -        strncpy((char *)h->oem_table_id, oem_table_id, sizeof(h->oem_table_id));
> +        strpadcpy((char *)h->oem_table_id, sizeof(h->oem_table_id),
> +                  oem_table_id, '\0');
>      } else {
>          memcpy(h->oem_table_id, ACPI_BUILD_APPNAME4, 4);
>          memcpy(h->oem_table_id + 4, sig, 4);
> diff --git a/hw/acpi/core.c b/hw/acpi/core.c
> index aafdc61648..6e8f4e5713 100644
> --- a/hw/acpi/core.c
> +++ b/hw/acpi/core.c
> @@ -31,6 +31,7 @@
>  #include "qapi/qapi-visit-misc.h"
>  #include "qemu/error-report.h"
>  #include "qemu/option.h"
> +#include "qemu/cutils.h"
>  
>  struct acpi_table_header {
>      uint16_t _length;         /* our length, not actual part of the hdr */
> @@ -181,7 +182,7 @@ static void acpi_table_install(const char unsigned *blob, size_t bloblen,
>      ext_hdr->_length = cpu_to_le16(acpi_payload_size);
>  
>      if (hdrs->has_sig) {
> -        strncpy(ext_hdr->sig, hdrs->sig, sizeof ext_hdr->sig);
> +        strpadcpy(ext_hdr->sig, sizeof ext_hdr->sig, hdrs->sig, '\0');
>          ++changed_fields;
>      }
>  
> @@ -200,12 +201,12 @@ static void acpi_table_install(const char unsigned *blob, size_t bloblen,
>      ext_hdr->checksum = 0;
>  
>      if (hdrs->has_oem_id) {
> -        strncpy(ext_hdr->oem_id, hdrs->oem_id, sizeof ext_hdr->oem_id);
> +        strpadcpy(ext_hdr->oem_id, sizeof ext_hdr->oem_id, hdrs->oem_id, '\0');
>          ++changed_fields;
>      }
>      if (hdrs->has_oem_table_id) {
> -        strncpy(ext_hdr->oem_table_id, hdrs->oem_table_id,
> -                sizeof ext_hdr->oem_table_id);
> +        strpadcpy(ext_hdr->oem_table_id, sizeof ext_hdr->oem_table_id,
> +                  hdrs->oem_table_id, '\0');
>          ++changed_fields;
>      }
>      if (hdrs->has_oem_rev) {
> @@ -213,8 +214,8 @@ static void acpi_table_install(const char unsigned *blob, size_t bloblen,
>          ++changed_fields;
>      }
>      if (hdrs->has_asl_compiler_id) {
> -        strncpy(ext_hdr->asl_compiler_id, hdrs->asl_compiler_id,
> -                sizeof ext_hdr->asl_compiler_id);
> +        strpadcpy(ext_hdr->asl_compiler_id, sizeof ext_hdr->asl_compiler_id,
> +                  hdrs->asl_compiler_id, '\0');
>          ++changed_fields;
>      }
>      if (hdrs->has_asl_compiler_rev) {



On Tue, Dec 18, 2018 at 12:03:30PM +0100, Philippe Mathieu-Daudé wrote:
> GCC 8 new warning prevents builds to success since quite some time.
> First report on the mailing list is in July 2018:
> https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg03723.html
> 
> Various intents has been sent to fix this:
> - Incorrectly using g_strlcpy()
>   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03705.html
>   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03706.html
> - Using assert() and strpadcpy()
>   https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03938.html
> - Use #pragma GCC diagnostic ignored "-Wstringop-truncation"
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> - adding an inline wrapper with said pragma in there
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> - -Wno-stringop-truncation is the makefile
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> 
> This series replace the strncpy() calls by strpadcpy() which seemed
> to me the saniest option.
> 
> Regards,
> 
> Phil.

Do you happen to know why does it build fine with
Gcc 8.2.1?

Reading the GCC manual it seems that
there is a "nostring" attribute that means
"might not be 0 terminated".
I think we should switch to that which fixes the warning
but also warns if someone tries to misuse these
as C-strings.

Seems to be a better option, does it not?


> Marc-André Lureau (1):
>   hw/acpi: Replace strncpy() by strpadcpy(pad='\0')
> 
> Philippe Mathieu-Daudé (2):
>   block/sheepdog: Replace strncpy() by strpadcpy(pad='\0')
>   migration: Replace strncpy() by strpadcpy(pad='\0')
> 
>  block/sheepdog.c         |  6 +++---
>  hw/acpi/aml-build.c      |  6 ++++--
>  hw/acpi/core.c           | 13 +++++++------
>  migration/global_state.c |  4 ++--
>  4 files changed, 16 insertions(+), 13 deletions(-)
> 
> -- 
> 2.17.2


On Tue, Dec 18, 2018 at 09:31:00AM -0500, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2018 at 12:03:30PM +0100, Philippe Mathieu-Daudé wrote:
> > GCC 8 new warning prevents builds to success since quite some time.
> > First report on the mailing list is in July 2018:
> > https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg03723.html
> > 
> > Various intents has been sent to fix this:
> > - Incorrectly using g_strlcpy()
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03705.html
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03706.html
> > - Using assert() and strpadcpy()
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03938.html
> > - Use #pragma GCC diagnostic ignored "-Wstringop-truncation"
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> > - adding an inline wrapper with said pragma in there
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> > - -Wno-stringop-truncation is the makefile
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> > 
> > This series replace the strncpy() calls by strpadcpy() which seemed
> > to me the saniest option.
> > 
> > Regards,
> > 
> > Phil.
> 
> Do you happen to know why does it build fine with
> Gcc 8.2.1?
> 
> Reading the GCC manual it seems that
> there is a "nostring" attribute that means

typo - its "nonstring"

> "might not be 0 terminated".
> I think we should switch to that which fixes the warning
> but also warns if someone tries to misuse these
> as C-strings.
> 
> Seems to be a better option, does it not?

Yes, it does look best as gcc manual explicitly suggests "nonstring"
as the way to stop this strncpy warning.


Regards,
Daniel
-- 
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On Tue, Dec 18, 2018 at 09:31:00AM -0500, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2018 at 12:03:30PM +0100, Philippe Mathieu-Daudé wrote:
> > GCC 8 new warning prevents builds to success since quite some time.
> > First report on the mailing list is in July 2018:
> > https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg03723.html
> > 
> > Various intents has been sent to fix this:
> > - Incorrectly using g_strlcpy()
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03705.html
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03706.html
> > - Using assert() and strpadcpy()
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03938.html
> > - Use #pragma GCC diagnostic ignored "-Wstringop-truncation"
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> > - adding an inline wrapper with said pragma in there
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> > - -Wno-stringop-truncation is the makefile
> >   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> > 
> > This series replace the strncpy() calls by strpadcpy() which seemed
> > to me the saniest option.
> > 
> > Regards,
> > 
> > Phil.
> 
> Do you happen to know why does it build fine with
> Gcc 8.2.1?
> 
> Reading the GCC manual it seems that
> there is a "nostring" attribute

Sorry that should be "nonstring".


> that means
> "might not be 0 terminated".
> I think we should switch to that which fixes the warning
> but also warns if someone tries to misuse these
> as C-strings.
> 
> Seems to be a better option, does it not?
> 

Also maybe we can make strpadcpy check for the nonstring
attribute too somehow?
Or did gcc just hardcode the strncpy name?

> > Marc-André Lureau (1):
> >   hw/acpi: Replace strncpy() by strpadcpy(pad='\0')
> > 
> > Philippe Mathieu-Daudé (2):
> >   block/sheepdog: Replace strncpy() by strpadcpy(pad='\0')
> >   migration: Replace strncpy() by strpadcpy(pad='\0')
> > 
> >  block/sheepdog.c         |  6 +++---
> >  hw/acpi/aml-build.c      |  6 ++++--
> >  hw/acpi/core.c           | 13 +++++++------
> >  migration/global_state.c |  4 ++--
> >  4 files changed, 16 insertions(+), 13 deletions(-)
> > 
> > -- 
> > 2.17.2


On Tue, Dec 18, 2018 at 03:45:08PM +0100, Paolo Bonzini wrote:
> On 18/12/18 15:31, Michael S. Tsirkin wrote:
> > Do you happen to know why does it build fine with
> > Gcc 8.2.1?
> > 
> > Reading the GCC manual it seems that
> > there is a "nostring" attribute that means
> > "might not be 0 terminated".
> > I think we should switch to that which fixes the warning
> > but also warns if someone tries to misuse these
> > as C-strings.
> > 
> > Seems to be a better option, does it not?
> > 
> > 
> 
> Using strpadcpy is clever and self-documenting, though.  We have it
> already, so why not use it.
> 
> Paolo

The advantage of nonstring is that it will catch attempts to
use these fields with functions that expect a 0 terminated string.

strpadcpy will instead just silence the warning.


-- 
MST


On Tue, Dec 18, 2018 at 05:38:17PM +0100, Paolo Bonzini wrote:
> On 18/12/18 15:54, Michael S. Tsirkin wrote:
> > On Tue, Dec 18, 2018 at 03:45:08PM +0100, Paolo Bonzini wrote:
> >> On 18/12/18 15:31, Michael S. Tsirkin wrote:
> >>> Do you happen to know why does it build fine with
> >>> Gcc 8.2.1?
> >>>
> >>> Reading the GCC manual it seems that
> >>> there is a "nostring" attribute that means
> >>> "might not be 0 terminated".
> >>> I think we should switch to that which fixes the warning
> >>> but also warns if someone tries to misuse these
> >>> as C-strings.
> >>>
> >>> Seems to be a better option, does it not?
> >>>
> >>>
> >>
> >> Using strpadcpy is clever and self-documenting, though.  We have it
> >> already, so why not use it.
> >>
> >> Paolo
> > 
> > The advantage of nonstring is that it will catch attempts to
> > use these fields with functions that expect a 0 terminated string.
> > 
> > strpadcpy will instead just silence the warning.
> 
> Ah, I see.  We could also do both, that's a matter of taste.
> 
> Paolo

Do you happen to know how to make gcc check the buffer size
for strpadcpy? Is the name strncpy just hard-coded?

-- 
MST


On Tue, Dec 18, 2018 at 05:55:27PM +0100, Philippe Mathieu-Daudé wrote:
> On 12/18/18 3:54 PM, Michael S. Tsirkin wrote:
> > On Tue, Dec 18, 2018 at 03:45:08PM +0100, Paolo Bonzini wrote:
> >> On 18/12/18 15:31, Michael S. Tsirkin wrote:
> >>> Do you happen to know why does it build fine with
> >>> Gcc 8.2.1?
> >>>
> >>> Reading the GCC manual it seems that
> >>> there is a "nostring" attribute that means
> >>> "might not be 0 terminated".
> >>> I think we should switch to that which fixes the warning
> >>> but also warns if someone tries to misuse these
> >>> as C-strings.
> >>>
> >>> Seems to be a better option, does it not?
> >>>
> >>>
> >>
> >> Using strpadcpy is clever and self-documenting, though.  We have it
> >> already, so why not use it.
> >>
> >> Paolo
> > 
> > The advantage of nonstring is that it will catch attempts to
> > use these fields with functions that expect a 0 terminated string.
> > 
> > strpadcpy will instead just silence the warning.
> 
> migration/global_state.c:109:15: error: 'strlen' argument 1 declared
> attribute 'nonstring' [-Werror=stringop-overflow=]
>      s->size = strlen((char *)s->runstate) + 1;
>                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> GCC won... It is true this strlen() is buggy, indeed s->runstate might
> be not NUL-terminated.


Ooh nice. I smell some CVE fixes coming from this effort.


-- 
MST


On Tue, Dec 18, 2018 at 06:12:05PM +0100, Paolo Bonzini wrote:
> On 18/12/18 17:55, Philippe Mathieu-Daudé wrote:
> >> strpadcpy will instead just silence the warning.
> > migration/global_state.c:109:15: error: 'strlen' argument 1 declared
> > attribute 'nonstring' [-Werror=stringop-overflow=]
> >      s->size = strlen((char *)s->runstate) + 1;
> >                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > GCC won... It is true this strlen() is buggy, indeed s->runstate might
> > be not NUL-terminated.
> 
> No, runstate is declared as an array of 100 bytes, which are more than
> enough.  It's ugly code but not buggy.
> 
> Paolo

Yes ... but it is loaded using
        VMSTATE_BUFFER(runstate, GlobalState),
and parsed using qapi_enum_parse which does not get
the buffer length.

So unless we are lucky there's a buffer overrun
on a remote/file input here.

Seems buggy to me - what am I missing?

-- 
MST


On Tue, Dec 18, 2018 at 12:03:34PM -0500, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2018 at 05:38:17PM +0100, Paolo Bonzini wrote:
> > On 18/12/18 15:54, Michael S. Tsirkin wrote:
> > > On Tue, Dec 18, 2018 at 03:45:08PM +0100, Paolo Bonzini wrote:
> > >> On 18/12/18 15:31, Michael S. Tsirkin wrote:
> > >>> Do you happen to know why does it build fine with
> > >>> Gcc 8.2.1?
> > >>>
> > >>> Reading the GCC manual it seems that
> > >>> there is a "nostring" attribute that means
> > >>> "might not be 0 terminated".
> > >>> I think we should switch to that which fixes the warning
> > >>> but also warns if someone tries to misuse these
> > >>> as C-strings.
> > >>>
> > >>> Seems to be a better option, does it not?
> > >>>
> > >>>
> > >>
> > >> Using strpadcpy is clever and self-documenting, though.  We have it
> > >> already, so why not use it.
> > >>
> > >> Paolo
> > > 
> > > The advantage of nonstring is that it will catch attempts to
> > > use these fields with functions that expect a 0 terminated string.
> > > 
> > > strpadcpy will instead just silence the warning.
> > 
> > Ah, I see.  We could also do both, that's a matter of taste.
> > 
> > Paolo
> 
> Do you happen to know how to make gcc check the buffer size
> for strpadcpy? Is the name strncpy just hard-coded?

GCC provides  strncpy as a builtin function and its warning only
checks its builtin.

Regards,
Daniel
-- 
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On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 introduced the -Wstringop-truncation checker to detect truncation by
> the strncat and strncpy functions (closely related to -Wstringop-overflow,
> which detect buffer overflow by string-modifying functions declared in
> <string.h>).

This paragraph talks about a new warning checker, but makes no mention 
of an attribute.

> 
> Add the QEMU_NONSTRING macro which checks if the compiler supports this
> attribute.

Thus, "this attribute" has no antecedent; did you forget to add a 
sentence to the previous paragraph, or maybe put the mention of adding 
QEMU_NONSTRING after...

> 
>>From the GCC manual [*]:
> 
>    The nonstring variable attribute specifies that an object or member
>    declaration with type array of char, signed char, or unsigned char,
>    or pointer to such a type is intended to store character arrays that
>    do not necessarily contain a terminating NUL. This is useful in detecting
>    uses of such arrays or pointers with functions that expect NUL-terminated
>    strings, and to avoid warnings when such an array or pointer is used as
>    an argument to a bounded string manipulation function such as strncpy.

...the explanation of how the attribute was added in tandem with the new 
warning checker for silencing specific instances of the warning?

> 
> [*] https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
> 
> Suggested-by: Michael S. Tsirkin <email address hidden>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>   include/qemu/compiler.h | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
> 

Reviewed-by: Eric Blake <email address hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>    The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>    bug 81117 is specifically intended to highlight likely unintended
>    uses of the strncpy function that truncate the terminating NUL
>    character from the source string.
> 
> This new warning leads to compilation failures:
> 
>      CC      block/sheepdog.o
>    qemu/block/sheepdog.c: In function 'find_vdi_name':
>    qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
>         strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1
> 
> As described previous to the strncpy() calls, the use of strncpy() is
> correct here:
> 
>      /* This pair of strncpy calls ensures that the buffer is zero-filled,
>       * which is desirable since we'll soon be sending those bytes, and
>       * don't want the send_req to read uninitialized data.
>       */
>      strncpy(buf, filename, SD_MAX_VDI_LEN);
>      strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> 
> Suggested-by: Michael S. Tsirkin <email address hidden>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>   block/sheepdog.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Eric Blake <email address hidden>

> 
> diff --git a/block/sheepdog.c b/block/sheepdog.c
> index 0125df9d49..d4ad6b119d 100644
> --- a/block/sheepdog.c
> +++ b/block/sheepdog.c
> @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s, const char *filename,
>       SheepdogVdiReq hdr;
>       SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
>       unsigned int wlen, rlen = 0;
> -    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> +    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
>   
>       fd = connect_to_sdog(s, errp);
>       if (fd < 0) {
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>    The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>    bug 81117 is specifically intended to highlight likely unintended
>    uses of the strncpy function that truncate the terminating NUL
>    character from the source string.
> 
> This new warning leads to compilation failures:
> 
>      CC      migration/global_state.o
>    qemu/migration/global_state.c: In function 'global_state_store_running':
>    qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
>         strncpy((char *)global_state.runstate, state, sizeof(global_state.runstate));
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> 
> Suggested-by: Michael S. Tsirkin <email address hidden>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>   migration/global_state.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Should this be squashed with 5/5?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 introduced the -Wstringop-overflow, which detect buffer overflow
> by string-modifying functions declared in <string.h>, such strncpy(),
> used in global_state_store_running().
> 
> Since the global_state.runstate does not necessarily contains a
> terminating NUL character, We had to use the QEMU_NONSTRING attribute.

s/We/we/

> 
> The GCC manual says about the nonstring attribute:
> 
>    However, when the array is declared with the attribute the call to
>    strlen is diagnosed because when the array doesn’t contain a
>    NUL-terminated string the call is undefined. [...]
>    In addition, calling strnlen and strndup with such arrays is safe
>    provided a suitable bound is specified, and not diagnosed.
> 
> GCC indeed found an incorrect use of strlen(), because this array
> is loaded by VMSTATE_BUFFER(runstate, GlobalState) then parsed
> using qapi_enum_parse which does not get the buffer length.
> 
> Use strnlen() which returns sizeof(s->runstate) if the array is not
> NUL-terminated.
> 
> This fixes:
> 
>      CC      migration/global_state.o
>    qemu/migration/global_state.c: In function 'global_state_pre_save':
>    qemu/migration/global_state.c:109:15: error: 'strlen' argument 1 declared attribute 'nonstring' [-Werror=stringop-overflow=]
>         s->size = strlen((char *)s->runstate) + 1;
>                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>    qemu/migration/global_state.c:24:13: note: argument 'runstate' declared here
>         uint8_t runstate[100] QEMU_NONSTRING;
>                 ^~~~~~~~
>    cc1: all warnings being treated as errors
>    make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
> 
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>   migration/global_state.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 6e19333422..c19030ef62 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -106,7 +106,7 @@ static int global_state_pre_save(void *opaque)
>       GlobalState *s = opaque;
>   
>       trace_migrate_global_state_pre_save((char *)s->runstate);
> -    s->size = strlen((char *)s->runstate) + 1;

The old code sets s->size to the string length + space for the NUL byte 
(by assuming that a NUL byte was present), and accidentally sets it 
beyond the s->runstate array if there was no NUL byte (our existing 
runstate names are shorter than 100 bytes, so this could only happen on 
a malicious stream).

> +    s->size = strnlen((char *)s->runstate, sizeof(s->runstate)) + 1;

The new code can still end up setting s->size beyond the array.  Is that 
intended, or would it be better to use strnlen(s->runstate, 
sizeof(s->runstate) - 1) + 1?

Also, as I argued on 4/5, why isn't this squashed in with the patch that 
marks the field NONSTRING?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>    The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>    bug 81117 is specifically intended to highlight likely unintended
>    uses of the strncpy function that truncate the terminating NUL
>    character from the source string.
> 
> This new warning leads to compilation failures:
> 
>      CC      migration/global_state.o
>    qemu/migration/global_state.c: In function 'global_state_store_running':
>    qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
>         strncpy((char *)global_state.runstate, state, sizeof(global_state.runstate));
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.

>   typedef struct {
>       uint32_t size;
> -    uint8_t runstate[100];
> +    uint8_t runstate[100] QEMU_NONSTRING;

Since 100 bytes for runstate[] is larger than any string possible in our 
current enum string values, could we instead add an assert that 
strlen(state) < sizeof(global_state.runstate), and then use strpadcpy() 
to make our intent obvious while still shutting up the compiler warning, 
but without having to deal with the fallout of marking runstate as a 
non-string?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


On Tue, Dec 18, 2018 at 06:51:17PM +0100, Philippe Mathieu-Daudé wrote:
> GCC 8 new warning prevents builds to success since quite some time.
> First report on the mailing list is in July 2018:
> https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg03723.html
> 
> Various intents has been sent to fix this:
> - Incorrectly using g_strlcpy()
>   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03705.html
>   https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03706.html
> - Using assert() and strpadcpy()
>   https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03938.html
> - Use #pragma GCC diagnostic ignored "-Wstringop-truncation"
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> - adding an inline wrapper with said pragma in there
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> - -Wno-stringop-truncation is the makefile
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04261.html
> - Use the 'nonstring' attribute
>   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04493.html
> 
> This series add the QEMU_NONSTRING definition and use it.
> 
> Regards,
> 
> Phil.


Reviewed-by: Michael S. Tsirkin <email address hidden>

> Philippe Mathieu-Daudé (5):
>   qemu/compiler: Define QEMU_NONSTRING
>   block/sheepdog: Use QEMU_NONSTRING for non NUL-terminated arrays
>   hw/acpi: Use QEMU_NONSTRING for non NUL-terminated arrays
>   migration: Use QEMU_NONSTRING for non NUL-terminated arrays
>   migration: Use strnlen() for fixed-size string
> 
>  block/sheepdog.c            |  2 +-
>  hw/acpi/core.c              |  8 ++++----
>  include/hw/acpi/acpi-defs.h |  8 ++++----
>  include/qemu/compiler.h     | 15 +++++++++++++++
>  migration/global_state.c    |  4 ++--
>  5 files changed, 26 insertions(+), 11 deletions(-)
> 
> -- 
> 2.17.2


On Tue, Dec 18, 2018 at 06:51:19PM +0100, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
> 
> This new warning leads to compilation failures:
> 
>     CC      block/sheepdog.o
>   qemu/block/sheepdog.c: In function 'find_vdi_name':
>   qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
>        strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1
> 
> As described previous to the strncpy() calls, the use of strncpy() is
> correct here:
> 
>     /* This pair of strncpy calls ensures that the buffer is zero-filled,
>      * which is desirable since we'll soon be sending those bytes, and
>      * don't want the send_req to read uninitialized data.
>      */
>     strncpy(buf, filename, SD_MAX_VDI_LEN);
>     strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> 
> Suggested-by: Michael S. Tsirkin <email address hidden>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>  block/sheepdog.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/sheepdog.c b/block/sheepdog.c
> index 0125df9d49..d4ad6b119d 100644
> --- a/block/sheepdog.c
> +++ b/block/sheepdog.c
> @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s, const char *filename,
>      SheepdogVdiReq hdr;
>      SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
>      unsigned int wlen, rlen = 0;
> -    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> +    QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];

In case you decide to respin anyway - this would be
a bit nicer as:
	char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN] QEMU_NONSTRING




>      fd = connect_to_sdog(s, errp);
>      if (fd < 0) {
> -- 
> 2.17.2


On Tue, Dec 18, 2018 at 06:51:22PM +0100, Philippe Mathieu-Daudé wrote:
> GCC 8 introduced the -Wstringop-overflow, which detect buffer overflow
> by string-modifying functions declared in <string.h>, such strncpy(),
> used in global_state_store_running().
> 
> Since the global_state.runstate does not necessarily contains a
> terminating NUL character, We had to use the QEMU_NONSTRING attribute.
> 
> The GCC manual says about the nonstring attribute:
> 
>   However, when the array is declared with the attribute the call to
>   strlen is diagnosed because when the array doesn’t contain a
>   NUL-terminated string the call is undefined. [...]
>   In addition, calling strnlen and strndup with such arrays is safe
>   provided a suitable bound is specified, and not diagnosed.
> 
> GCC indeed found an incorrect use of strlen(), because this array
> is loaded by VMSTATE_BUFFER(runstate, GlobalState) then parsed
> using qapi_enum_parse which does not get the buffer length.
> 
> Use strnlen() which returns sizeof(s->runstate) if the array is not
> NUL-terminated.
> 
> This fixes:
> 
>     CC      migration/global_state.o
>   qemu/migration/global_state.c: In function 'global_state_pre_save':
>   qemu/migration/global_state.c:109:15: error: 'strlen' argument 1 declared attribute 'nonstring' [-Werror=stringop-overflow=]
>        s->size = strlen((char *)s->runstate) + 1;
>                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>   qemu/migration/global_state.c:24:13: note: argument 'runstate' declared here
>        uint8_t runstate[100] QEMU_NONSTRING;
>                ^~~~~~~~
>   cc1: all warnings being treated as errors
>   make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
> 
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>  migration/global_state.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 6e19333422..c19030ef62 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -106,7 +106,7 @@ static int global_state_pre_save(void *opaque)
>      GlobalState *s = opaque;
>  
>      trace_migrate_global_state_pre_save((char *)s->runstate);
> -    s->size = strlen((char *)s->runstate) + 1;
> +    s->size = strnlen((char *)s->runstate, sizeof(s->runstate)) + 1;
>  
>      return 0;

I don't think this works correctly if strnlen returns
sizeof(s->runstate). Which never happens so we probably should
jus add

	assert(e->size is <= sizeof(s->runstate));

But also I think this is not enough, there's a problem in post-load
in the call to qapi_enum_parse. You probably want to force
the last character to 0 there.


>  }
> -- 
> 2.17.2


On Tue, 18 Dec 2018 18:51:20 +0100
Philippe Mathieu-Daudé <email address hidden> wrote:

> GCC 8 added a -Wstringop-truncation warning:
> 
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
> 
> This new warning leads to compilation failures:
> 
>     CC      hw/acpi/core.o
>   In function 'acpi_table_install', inlined from 'acpi_table_add' at qemu/hw/acpi/core.c:296:5:
>   qemu/hw/acpi/core.c:184:9: error: 'strncpy' specified bound 4 equals destination size [-Werror=stringop-truncation]
>            strncpy(ext_hdr->sig, hdrs->sig, sizeof ext_hdr->sig);
>            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   make: *** [qemu/rules.mak:69: hw/acpi/core.o] Error 1
> 
> Use the QEMU_NONSTRING attribute, since ACPI tables don't require the
> strings to be NUL-terminated.
> 
> Suggested-by: Michael S. Tsirkin <email address hidden>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>  hw/acpi/core.c              | 8 ++++----
>  include/hw/acpi/acpi-defs.h | 8 ++++----
>  2 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/acpi/core.c b/hw/acpi/core.c
> index aafdc61648..f60f750c3d 100644
> --- a/hw/acpi/core.c
> +++ b/hw/acpi/core.c
> @@ -35,14 +35,14 @@
>  struct acpi_table_header {
>      uint16_t _length;         /* our length, not actual part of the hdr */
>                                /* allows easier parsing for fw_cfg clients */
> -    char sig[4];              /* ACPI signature (4 ASCII characters) */
> +    char sig[4] QEMU_NONSTRING; /* ACPI signature (4 ASCII characters) */
>      uint32_t length;          /* Length of table, in bytes, including header */
>      uint8_t revision;         /* ACPI Specification minor version # */
>      uint8_t checksum;         /* To make sum of entire table == 0 */
> -    char oem_id[6];           /* OEM identification */
> -    char oem_table_id[8];     /* OEM table identification */
> +    char oem_id[6] QEMU_NONSTRING; /* OEM identification */
> +    char oem_table_id[8] QEMU_NONSTRING; /* OEM table identification */
>      uint32_t oem_revision;    /* OEM revision number */
> -    char asl_compiler_id[4];  /* ASL compiler vendor ID */
> +    char asl_compiler_id[4] QEMU_NONSTRING; /* ASL compiler vendor ID */
>      uint32_t asl_compiler_revision; /* ASL compiler revision number */
>  } QEMU_PACKED;
>  
> diff --git a/include/hw/acpi/acpi-defs.h b/include/hw/acpi/acpi-defs.h
> index af8e023968..3bf0bec8ba 100644
> --- a/include/hw/acpi/acpi-defs.h
> +++ b/include/hw/acpi/acpi-defs.h
> @@ -43,7 +43,7 @@ enum {
>  struct AcpiRsdpDescriptor {        /* Root System Descriptor Pointer */
>      uint64_t signature;              /* ACPI signature, contains "RSD PTR " */
>      uint8_t  checksum;               /* To make sum of struct == 0 */
> -    uint8_t  oem_id [6];             /* OEM identification */
> +    uint8_t  oem_id [6] QEMU_NONSTRING; /* OEM identification */
>      uint8_t  revision;               /* Must be 0 for 1.0, 2 for 2.0 */
>      uint32_t rsdt_physical_address;  /* 32-bit physical address of RSDT */
>      uint32_t length;                 /* XSDT Length in bytes including hdr */

you'll need to rebase this on top the latest Michael's pull request.
[PULL v2 25/30] hw: arm: Carry RSDP specific data through  AcpiRsdpData
[PULL v2 29/30] hw: acpi: Remove AcpiRsdpDescriptor and fix tests

> @@ -62,10 +62,10 @@ typedef struct AcpiRsdpDescriptor AcpiRsdpDescriptor;
>      uint32_t length;                 /* Length of table, in bytes, including header */ \
>      uint8_t  revision;               /* ACPI Specification minor version # */ \
>      uint8_t  checksum;               /* To make sum of entire table == 0 */ \
> -    uint8_t  oem_id [6];             /* OEM identification */ \
> -    uint8_t  oem_table_id [8];       /* OEM table identification */ \
> +    uint8_t  oem_id [6] QEMU_NONSTRING; /* OEM identification */ \
> +    uint8_t  oem_table_id [8] QEMU_NONSTRING; /* OEM table identification */ \
>      uint32_t oem_revision;           /* OEM revision number */ \
> -    uint8_t  asl_compiler_id [4];    /* ASL compiler vendor ID */ \
> +    uint8_t  asl_compiler_id [4] QEMU_NONSTRING; /* ASL compiler vendor ID */ \
>      uint32_t asl_compiler_revision;  /* ASL compiler revision number */
>  
>  



On Wed, 19 Dec 2018 10:20:36 +0100
Philippe Mathieu-Daudé <email address hidden> wrote:

> Le mer. 19 déc. 2018 10:16, Igor Mammedov <email address hidden> a écrit :
> 
> > On Tue, 18 Dec 2018 18:51:20 +0100
> > Philippe Mathieu-Daudé <email address hidden> wrote:
> >  
> > > GCC 8 added a -Wstringop-truncation warning:
> > >
> > >   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
> > >   bug 81117 is specifically intended to highlight likely unintended
> > >   uses of the strncpy function that truncate the terminating NUL
> > >   character from the source string.
> > >
> > > This new warning leads to compilation failures:
> > >
> > >     CC      hw/acpi/core.o
> > >   In function 'acpi_table_install', inlined from 'acpi_table_add' at  
> > qemu/hw/acpi/core.c:296:5:  
> > >   qemu/hw/acpi/core.c:184:9: error: 'strncpy' specified bound 4 equals  
> > destination size [-Werror=stringop-truncation]  
> > >            strncpy(ext_hdr->sig, hdrs->sig, sizeof ext_hdr->sig);
> > >            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >   make: *** [qemu/rules.mak:69: hw/acpi/core.o] Error 1
> > >
> > > Use the QEMU_NONSTRING attribute, since ACPI tables don't require the
> > > strings to be NUL-terminated.
> > >
> > > Suggested-by: Michael S. Tsirkin <email address hidden>
> > > Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> > > ---
> > >  hw/acpi/core.c              | 8 ++++----
> > >  include/hw/acpi/acpi-defs.h | 8 ++++----
> > >  2 files changed, 8 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/hw/acpi/core.c b/hw/acpi/core.c
> > > index aafdc61648..f60f750c3d 100644
> > > --- a/hw/acpi/core.c
> > > +++ b/hw/acpi/core.c
> > > @@ -35,14 +35,14 @@
> > >  struct acpi_table_header {
> > >      uint16_t _length;         /* our length, not actual part of the hdr  
> > */  
> > >                                /* allows easier parsing for fw_cfg  
> > clients */  
> > > -    char sig[4];              /* ACPI signature (4 ASCII characters) */
> > > +    char sig[4] QEMU_NONSTRING; /* ACPI signature (4 ASCII characters)  
> > */  
> > >      uint32_t length;          /* Length of table, in bytes, including  
> > header */  
> > >      uint8_t revision;         /* ACPI Specification minor version # */
> > >      uint8_t checksum;         /* To make sum of entire table == 0 */
> > > -    char oem_id[6];           /* OEM identification */
> > > -    char oem_table_id[8];     /* OEM table identification */
> > > +    char oem_id[6] QEMU_NONSTRING; /* OEM identification */
> > > +    char oem_table_id[8] QEMU_NONSTRING; /* OEM table identification */
> > >      uint32_t oem_revision;    /* OEM revision number */
> > > -    char asl_compiler_id[4];  /* ASL compiler vendor ID */
> > > +    char asl_compiler_id[4] QEMU_NONSTRING; /* ASL compiler vendor ID */
> > >      uint32_t asl_compiler_revision; /* ASL compiler revision number */
> > >  } QEMU_PACKED;
> > >
> > > diff --git a/include/hw/acpi/acpi-defs.h b/include/hw/acpi/acpi-defs.h
> > > index af8e023968..3bf0bec8ba 100644
> > > --- a/include/hw/acpi/acpi-defs.h
> > > +++ b/include/hw/acpi/acpi-defs.h
> > > @@ -43,7 +43,7 @@ enum {
> > >  struct AcpiRsdpDescriptor {        /* Root System Descriptor Pointer */
> > >      uint64_t signature;              /* ACPI signature, contains "RSD  
> > PTR " */  
> > >      uint8_t  checksum;               /* To make sum of struct == 0 */
> > > -    uint8_t  oem_id [6];             /* OEM identification */
> > > +    uint8_t  oem_id [6] QEMU_NONSTRING; /* OEM identification */
> > >      uint8_t  revision;               /* Must be 0 for 1.0, 2 for 2.0 */
> > >      uint32_t rsdt_physical_address;  /* 32-bit physical address of RSDT  
> > */  
> > >      uint32_t length;                 /* XSDT Length in bytes including  
> > hdr */
> >
> > you'll need to rebase this on top the latest Michael's pull request.
> > [PULL v2 25/30] hw: arm: Carry RSDP specific data through  AcpiRsdpData
> > [PULL v2 29/30] hw: acpi: Remove AcpiRsdpDescriptor and fix tests
> >  
> 
> OK. Can I add your Ack-by then?
pls note that new AcpiRsdpData has oem_id field that needs the same treatment

with rebase
Reviewed-by: Igor Mammedov <email address hidden>

> 
> > @@ -62,10 +62,10 @@ typedef struct AcpiRsdpDescriptor AcpiRsdpDescriptor;  
> > >      uint32_t length;                 /* Length of table, in bytes,  
> > including header */ \  
> > >      uint8_t  revision;               /* ACPI Specification minor  
> > version # */ \  
> > >      uint8_t  checksum;               /* To make sum of entire table ==  
> > 0 */ \  
> > > -    uint8_t  oem_id [6];             /* OEM identification */ \
> > > -    uint8_t  oem_table_id [8];       /* OEM table identification */ \
> > > +    uint8_t  oem_id [6] QEMU_NONSTRING; /* OEM identification */ \
> > > +    uint8_t  oem_table_id [8] QEMU_NONSTRING; /* OEM table  
> > identification */ \  
> > >      uint32_t oem_revision;           /* OEM revision number */ \
> > > -    uint8_t  asl_compiler_id [4];    /* ASL compiler vendor ID */ \
> > > +    uint8_t  asl_compiler_id [4] QEMU_NONSTRING; /* ASL compiler vendor  
> > ID */ \  
> > >      uint32_t asl_compiler_revision;  /* ASL compiler revision number */
> > >
> > >  
> >
> >  



On Wed, 19 Dec 2018 14:00:37 +0100
Andrew Jones <email address hidden> wrote:

> On Wed, Dec 19, 2018 at 01:43:40PM +0100, Philippe Mathieu-Daudé wrote:
> > Hi Drew,
> > 
> > On 12/19/18 11:10 AM, Andrew Jones wrote:
> > > On Tue, Dec 18, 2018 at 06:51:20PM +0100, Philippe Mathieu-Daudé wrote:
> > >> GCC 8 added a -Wstringop-truncation warning:
> > >>
> > >>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
> > >>   bug 81117 is specifically intended to highlight likely unintended
> > >>   uses of the strncpy function that truncate the terminating NUL
> > >>   character from the source string.
> > >>
> > >> This new warning leads to compilation failures:
> > >>
> > >>     CC      hw/acpi/core.o
> > >>   In function 'acpi_table_install', inlined from 'acpi_table_add' at qemu/hw/acpi/core.c:296:5:
> > >>   qemu/hw/acpi/core.c:184:9: error: 'strncpy' specified bound 4 equals destination size [-Werror=stringop-truncation]
> > >>            strncpy(ext_hdr->sig, hdrs->sig, sizeof ext_hdr->sig);
> > >>            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >>   make: *** [qemu/rules.mak:69: hw/acpi/core.o] Error 1
> > >>
> > >> Use the QEMU_NONSTRING attribute, since ACPI tables don't require the
> > >> strings to be NUL-terminated.
> > > 
> > > Aren't we always starting with zero-initialized structures in ACPI code?
> > > If so, then we should be able to change the strncpy's to memcpy's.
> > 
> > The first call zero-initializes, but then we call realloc():
> > 
> >     /* We won't fail from here on. Initialize / extend the globals. */
> >     if (acpi_tables == NULL) {
> >         acpi_tables_len = sizeof(uint16_t);
> >         acpi_tables = g_malloc0(acpi_tables_len);
> >     }
> > 
> >     acpi_tables = g_realloc(acpi_tables, acpi_tables_len +
> >                                          ACPI_TABLE_PFX_SIZE +
> >                                          sizeof dfl_hdr + body_size);
> > 
> >     ext_hdr = (struct acpi_table_header *)(acpi_tables +
> >                                            acpi_tables_len);
> > 
> > So memcpy() isn't enough.
> 
> Ah, thanks.
> 
> > 
> > I can resend the previous patch which uses strpadcpy() if you prefer,
> > Igor already reviewed it:
> > 
> > https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04406.html
> >
> 
> I do like strpadcpy() better, but I'm not going to lose sleep about
> this either way it goes.
I'm ok with both ways, but v2 consensus was to use QEMU_NONSTRING if I got it right

> 
> Thanks,
> drew 



* Philippe Mathieu-Daudé (<email address hidden>) wrote:
> GCC 8 added a -Wstringop-truncation warning:
> 
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
> 
> This new warning leads to compilation failures:
> 
>     CC      migration/global_state.o
>   qemu/migration/global_state.c: In function 'global_state_store_running':
>   qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
>        strncpy((char *)global_state.runstate, state, sizeof(global_state.runstate));
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
> 
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> 
> Suggested-by: Michael S. Tsirkin <email address hidden>
> Signed-off-by: Philippe Mathieu-Daudé <email address hidden>
> ---
>  migration/global_state.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 8e8ab5c51e..6e19333422 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -21,7 +21,7 @@
>  
>  typedef struct {
>      uint32_t size;
> -    uint8_t runstate[100];
> +    uint8_t runstate[100] QEMU_NONSTRING;

Hmm; global_state_post_load needs to be fixed for this;  it
uses s->runsate and ends up passing it to both a trace
and a qapi_enum_parse - so it's really treating it as a string.
That code is unsafe anyway since it's assuming the received
runstate would be terminated.

Dave

>      RunState state;
>      bool received;
>  } GlobalState;
> -- 
> 2.17.2
> 
--
Dr. David Alan Gilbert / <email address hidden> / Manchester, UK


We think we've fixed all the GCC 8.2 stringop-truncation warnings now, so current QEMU git master and the 4.0 rc1 we've just tagged should both build cleanly. Please reopen the bug if we missed one somehow.