diff options
| -rw-r--r-- | arch/x86/entry/vdso/vdso32/sigreturn.S | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/arch/x86/entry/vdso/vdso32/sigreturn.S b/arch/x86/entry/vdso/vdso32/sigreturn.S index b433353bc8e3..b33fcc501ba3 100644 --- a/arch/x86/entry/vdso/vdso32/sigreturn.S +++ b/arch/x86/entry/vdso/vdso32/sigreturn.S @@ -35,9 +35,38 @@ #endif .endm +/* + * WARNING: + * + * A bug in the libgcc unwinder as of at least gcc 15.2 (2026) means that + * the unwinder fails to recognize the signal frame flag. + * + * There is a hacky legacy fallback path in libgcc which ends up + * getting invoked instead. It happens to work as long as BOTH of the + * following conditions are true: + * + * 1. There is at least one byte before the each of the sigreturn + * functions which falls outside any function. This is enforced by + * an explicit nop instruction before the ALIGN. + * 2. The code sequences between the entry point up to and including + * the int $0x80 below need to match EXACTLY. Do not change them + * in any way. The exact byte sequences are: + * + * __kernel_sigreturn: + * 0: 58 pop %eax + * 1: b8 77 00 00 00 mov $0x77,%eax + * 6: cd 80 int $0x80 + * + * __kernel_rt_sigreturn: + * 0: b8 ad 00 00 00 mov $0xad,%eax + * 5: cd 80 int $0x80 + * + * For details, see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124050 + */ .text .globl __kernel_sigreturn .type __kernel_sigreturn,@function + nop /* libgcc hack: see comment above */ ALIGN __kernel_sigreturn: STARTPROC_SIGNAL_FRAME IA32_SIGFRAME_sigcontext @@ -52,6 +81,7 @@ SYM_INNER_LABEL(vdso32_sigreturn_landing_pad, SYM_L_GLOBAL) .globl __kernel_rt_sigreturn .type __kernel_rt_sigreturn,@function + nop /* libgcc hack: see comment above */ ALIGN __kernel_rt_sigreturn: STARTPROC_SIGNAL_FRAME IA32_RT_SIGFRAME_sigcontext |