Commit f05058c4d652 supposedly "forces a stack frame to be created before the inline asm code if CONFIG_FRAME_POINTER is enabled by listing the stack pointer as an output operand for the get_user() inline assembly statement.". This doesn't work as intended, at least with gcc v4.9.2 and x86-64 the generated code is exactly the same with and without the patch. However clang adds an extra instruction that adjusts %rsp, which ends up causing double faults all over the place.
Signed-off-by: Matthias Kaehlcke <[email protected]> --- arch/x86/include/asm/uaccess.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 476ea27f490b..9ec2beab73df 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -161,11 +161,10 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) ({ \ int __ret_gu; \ register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \ - register void *__sp asm(_ASM_SP); \ __chk_user_ptr(ptr); \ might_fault(); \ - asm volatile("call __get_user_%P4" \ - : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ + asm volatile("call __get_user_%P3" \ + : "=a" (__ret_gu), "=r" (__val_gu) \ : "0" (ptr), "i" (sizeof(*(ptr)))); \ (x) = (__force __typeof__(*(ptr))) __val_gu; \ __builtin_expect(__ret_gu, 0); \ -- 2.13.2.932.g7449e964c-goog
