Messages in this thread Patch in this message | | | Date | Sun, 12 May 2024 07:55:28 +0300 | From | Alexey Dobriyan <> | Subject | [PATCH] x86/vdso: add rcx clobber in syscall gettimeofday fallback |
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syscall instruction in fallback code is missing "rcx" and "r11" clobbers.
It doesn't seem to cause any problems because the C code looks like:
if (do_hres(&vd[CS_HRES_COARSE], CLOCK_REALTIME, &ts)) return gettimeofday_fallback(tv, tz);
and assembly looks like
__vdso_gettimeofday: 0: lea r9, [rip] 7: test rdi,rdi a: je b7 10: mov r8d, [r9] 13: test r8b, 1 17: jne bf 1d: cmp [rip], 1 24: jne c6 2a: rdtsc
c6: mov eax, 96 cb: syscall ====> cd: ret <====
rcx and r11 are caller-saved and nothing seems to use those registers after syscall and before returning from vDSO.
Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation") Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> ---
arch/x86/include/asm/vdso/gettimeofday.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/include/asm/vdso/gettimeofday.h +++ b/arch/x86/include/asm/vdso/gettimeofday.h @@ -86,7 +86,7 @@ long gettimeofday_fallback(struct __kernel_old_timeval *_tv, long ret; asm("syscall" : "=a" (ret) : - "0" (__NR_gettimeofday), "D" (_tv), "S" (_tz) : "memory"); + "0" (__NR_gettimeofday), "D" (_tv), "S" (_tz) : "rcx", "r11", "memory"); return ret; }
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