diff options
Diffstat (limited to 'gitlab/issues_text/target_missing/host_missing/accel_missing/1489')
| -rw-r--r-- | gitlab/issues_text/target_missing/host_missing/accel_missing/1489 | 94 |
1 files changed, 0 insertions, 94 deletions
diff --git a/gitlab/issues_text/target_missing/host_missing/accel_missing/1489 b/gitlab/issues_text/target_missing/host_missing/accel_missing/1489 deleted file mode 100644 index 96f7d5c53..000000000 --- a/gitlab/issues_text/target_missing/host_missing/accel_missing/1489 +++ /dev/null @@ -1,94 +0,0 @@ -Breakpoints set at wrong addresses in `test-gdbstub.py` for some Linux kernels guest images -Description of problem: -The script `tests/guest-debug/test-gdbstub.py` for testing QEMU's GDB -stub on Linux kernel guests sets breakpoints on `kernel_init()` and -`wait_for_completion()`. As the script is coded, breakpoints are set -(implicitly) not at the functions' start addresses, but at the end of -the functions' prologues. - -For some Linux kernel builds in which `kernel_init()` and -`wait_for_completion()` get compiled with a function prologue, the -script fails to detect breakpoint hits in `check_hbreak()` and -`check_break()` because it compares the stopped address (i.e. the end of -the function's prologue) with the function's start address, and they -differ. To observe the difference in GDB: - -```sh -$ gdb -q --nx vmlinux -Reading symbols from vmlinux... -(gdb) b kernel_init -Breakpoint 1 at 0xffff800008fbeb28: file init/main.c, line 1497. # <- prologue start -(gdb) b *kernel_init -Breakpoint 2 at 0xffff800008fbeb18: file init/main.c, line 1491. # <- function start -``` - -In my tests, the issue doesn't occur with standard Linux kernels builds -(e.g. compiled on Linux hosts with GCC) because typically both -`kernel_init()` and `wait_for_completion()` seem to be without -prologues. -Steps to reproduce: -The issue has so far been encountered only with arm64 Linux kernel -guests compiled on macOS arm64 with -[mac-linux-kdk](https://github.com/GayPizzaSpecifications/mac-linux-kdk). - -1. Compile a recent arm64 Linux kernel on macOS arm64 with debugging - information (first `make defconfig`, then `make menuconfig` and set - `Kernel hacking / Compile-time checks and compiler options / Debug - information / Rely on toolchain's implicit default DWARF version`) - - ```sh - $ file /tmp/linux-5.19/arch/arm64/boot/Image - /tmp/linux-5.19/arch/arm64/boot/Image: Linux kernel ARM64 boot executable Image, little-endian, 4K pages - $ file /tmp/linux-5.19/vmlinux - /tmp/linux-5.19/vmlinux: ELF 64-bit LSB pie executable, ARM aarch64, version 1 (SYSV), statically linked, BuildID[sha1]=bf9e422d48e0aded5859fe34d6de2c174ef3a20b, with debug_info, not stripped - ``` - -2. Start QEMU waiting for GDB to connect: - - ```sh - $ ./qemu-system-aarch64 -smp 1 -M virt -cpu cortex-a57 -kernel /tmp/linux-5.19/arch/arm64/boot/Image -append nokaslr -s -S - ``` - -3. Execute the `test-gdbstub.py` script (as described in the script file - itself): - - ```sh - $ gdb /tmp/linux-5.19/vmlinux -x tests/guest-debug/test-gdbstub.py - ``` - - The script then hangs. - -Tested both on a macOS host and a Linux host. -Additional information: -The proposed fix is to explicitly disable GDB's prologue decoder and set -the two breakpoints at the functions' start addresses [by adding an -asterisk before the function -name](https://stackoverflow.com/a/31451340): - -```diff -diff --git a/tests/guest-debug/test-gdbstub.py b/tests/guest-debug/test-gdbstub.py -index 98a5df4d4..6202d17c3 100644 ---- a/tests/guest-debug/test-gdbstub.py -+++ b/tests/guest-debug/test-gdbstub.py -@@ -31,7 +31,7 @@ def check_step(): - def check_break(sym_name): - "Setup breakpoint, continue and check we stopped." - sym, ok = gdb.lookup_symbol(sym_name) -- bp = gdb.Breakpoint(sym_name) -+ bp = gdb.Breakpoint("*%s" % (sym_name)) - - gdb.execute("c") - -@@ -48,7 +48,7 @@ def check_break(sym_name): - def check_hbreak(sym_name): - "Setup hardware breakpoint, continue and check we stopped." - sym, ok = gdb.lookup_symbol(sym_name) -- gdb.execute("hbreak %s" % (sym_name)) -+ gdb.execute("hbreak *%s" % (sym_name)) - gdb.execute("c") - - # hopefully we came back -``` - -This change shouldn't impact the Linux kernel guests for which the -script is already working as intended. |