diff options
| author | Will Deacon <will@kernel.org> | 2020-05-19 12:38:33 +0100 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2020-05-21 12:57:18 +0100 |
| commit | 9a964285572b5a3ea268bd744bb6837aecf09640 (patch) | |
| tree | 76d5243ccaff584ad1d4660c3ed259446bf1a4c5 /arch/arm64/kernel/vdso | |
| parent | e4e9f6dfeedc86afef2c3fa4102d274862fe2cf9 (diff) | |
arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction
For better or worse, GDB relies on the exact instruction sequence in the
VDSO sigreturn trampoline in order to unwind from signals correctly.
Commit c91db232da48 ("arm64: vdso: Convert to modern assembler annotations")
unfortunately added a BTI C instruction to the start of __kernel_rt_sigreturn,
which breaks this check. Thankfully, it's also not required, since the
trampoline is called from a RET instruction when returning from the signal
handler
Remove the unnecessary BTI C instruction from __kernel_rt_sigreturn,
and do the same for the 32-bit VDSO as well for good measure.
Cc: Daniel Kiss <daniel.kiss@arm.com>
Cc: Tamas Zsoldos <tamas.zsoldos@arm.com>
Reviewed-by: Dave Martin <dave.martin@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Fixes: c91db232da48 ("arm64: vdso: Convert to modern assembler annotations")
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/kernel/vdso')
| -rw-r--r-- | arch/arm64/kernel/vdso/sigreturn.S | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S index 3fb13b81f780..0c921130002a 100644 --- a/arch/arm64/kernel/vdso/sigreturn.S +++ b/arch/arm64/kernel/vdso/sigreturn.S @@ -15,7 +15,14 @@ .text nop -SYM_FUNC_START(__kernel_rt_sigreturn) +/* + * GDB relies on being able to identify the sigreturn instruction sequence to + * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START() + * here, as it will emit a BTI C instruction and break the unwinder. Thankfully, + * this function is only ever called from a RET and so omitting the landing pad + * is perfectly fine. + */ +SYM_CODE_START(__kernel_rt_sigreturn) .cfi_startproc .cfi_signal_frame .cfi_def_cfa x29, 0 @@ -24,6 +31,6 @@ SYM_FUNC_START(__kernel_rt_sigreturn) mov x8, #__NR_rt_sigreturn svc #0 .cfi_endproc -SYM_FUNC_END(__kernel_rt_sigreturn) +SYM_CODE_END(__kernel_rt_sigreturn) emit_aarch64_feature_1_and |