6.15-stable review patch. If anyone has any objections, please let me know.
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From: Thomas Weißschuh thomas.weissschuh@linutronix.de
commit e242bbbb6d7ac7556aa1e358294dc7e3c82cc902 upstream.
The syscall wrappers use the "a0" register for two different register variables, both the first argument and the return value. Here the "ret" variable is used as both input and output while the argument register is only used as input. Clang treats the conflicting input parameters as an undefined behaviour and optimizes away the argument assignment.
The code seems to work by chance for the most part today but that may change in the future. Specifically clock_gettime_fallback() fails with clockids from 16 to 23, as implemented by the upcoming auxiliary clocks.
Switch the "ret" register variable to a pure output, similar to the other architectures' vDSO code. This works in both clang and GCC.
Link: https://lore.kernel.org/lkml/20250602102825-42aa84f0-23f1-4d10-89fc-e8bbaffd... Link: https://lore.kernel.org/lkml/20250519082042.742926976@linutronix.de/ Fixes: c6b99bed6b8f ("LoongArch: Add VDSO and VSYSCALL support") Fixes: 18efd0b10e0f ("LoongArch: vDSO: Wire up getrandom() vDSO implementation") Cc: stable@vger.kernel.org Reviewed-by: Nathan Chancellor nathan@kernel.org Reviewed-by: Yanteng Si si.yanteng@linux.dev Reviewed-by: WANG Xuerui git@xen0n.name Reviewed-by: Xi Ruoyao xry111@xry111.site Signed-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de Signed-off-by: Huacai Chen chenhuacai@loongson.cn Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/loongarch/include/asm/vdso/getrandom.h | 2 +- arch/loongarch/include/asm/vdso/gettimeofday.h | 6 +++--- 2 files changed, 4 insertions(+), 4 deletions(-)
--- a/arch/loongarch/include/asm/vdso/getrandom.h +++ b/arch/loongarch/include/asm/vdso/getrandom.h @@ -20,7 +20,7 @@ static __always_inline ssize_t getrandom
asm volatile( " syscall 0\n" - : "+r" (ret) + : "=r" (ret) : "r" (nr), "r" (buffer), "r" (len), "r" (flags) : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7", "$t8", "memory"); --- a/arch/loongarch/include/asm/vdso/gettimeofday.h +++ b/arch/loongarch/include/asm/vdso/gettimeofday.h @@ -25,7 +25,7 @@ static __always_inline long gettimeofday
asm volatile( " syscall 0\n" - : "+r" (ret) + : "=r" (ret) : "r" (nr), "r" (tv), "r" (tz) : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7", "$t8", "memory"); @@ -44,7 +44,7 @@ static __always_inline long clock_gettim
asm volatile( " syscall 0\n" - : "+r" (ret) + : "=r" (ret) : "r" (nr), "r" (clkid), "r" (ts) : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7", "$t8", "memory"); @@ -63,7 +63,7 @@ static __always_inline int clock_getres_
asm volatile( " syscall 0\n" - : "+r" (ret) + : "=r" (ret) : "r" (nr), "r" (clkid), "r" (ts) : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7", "$t8", "memory");