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| author | Tony Garnock-Jones <tony.garnock-jones@glasgow.ac.uk> | 2018-09-08 19:22:05 +0100 |
|---|---|---|
| committer | Laurent Vivier <laurent@vivier.eu> | 2018-09-25 22:36:49 +0200 |
| commit | 58cfa6c2e6eb51b23cc98f81d16136b3ca929b31 (patch) | |
| tree | a46c07771d53fbf05dcf0da6e52d3831abe97314 /linux-user/syscall.c | |
| parent | 94894ff2d13c85a840f80387c573a34ed6c99063 (diff) | |
| download | focaccia-qemu-58cfa6c2e6eb51b23cc98f81d16136b3ca929b31.tar.gz focaccia-qemu-58cfa6c2e6eb51b23cc98f81d16136b3ca929b31.zip | |
linux-user: write(fd, NULL, 0) parity with linux's treatment of same
Bring linux-user write(2) handling into line with linux for the case
of a 0-byte write with a NULL buffer. Based on a patch originally
written by Zhuowei Zhang.
Addresses https://bugs.launchpad.net/qemu/+bug/1716292.
>From Zhuowei Zhang's patch (https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg08073.html):
Linux returns success for the special case of calling write with a
zero-length NULL buffer: compiling and running
int main() {
ssize_t ret = write(STDOUT_FILENO, NULL, 0);
fprintf(stderr, "write returned %ld\n", ret);
return 0;
}
gives "write returned 0" when run directly, but "write returned
-1" in QEMU.
This commit checks for this situation and returns success if
found.
Subsequent discussion raised the following questions (and my answers):
- Q. Should TARGET_NR_read pass through to safe_read in this
situation too?
A. I'm wary of changing unrelated code to the specific problem I'm
addressing. TARGET_NR_read is already consistent with Linux for
this case.
- Q. Do pread64/pwrite64 need to be changed similarly?
A. Experiment suggests not: both linux and linux-user yield -1 for
NULL 0-length reads/writes.
Signed-off-by: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20180908182205.GB409@mornington.dcs.gla.ac.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Diffstat (limited to 'linux-user/syscall.c')
| -rw-r--r-- | linux-user/syscall.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 58fb967499..019af632df 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -6772,6 +6772,9 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1, } return ret; case TARGET_NR_write: + if (arg2 == 0 && arg3 == 0) { + return get_errno(safe_write(arg1, 0, 0)); + } if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1))) return -TARGET_EFAULT; if (fd_trans_target_to_host_data(arg1)) { |