From 5bd0ab8af66829af74ed80cac767ce1c041fd767 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 4 Apr 2012 00:37:33 -0400 Subject: [PATCH] work around nasty gcc bug in the i386 syscall asm when the "r" (register) constraint is used to let gcc choose a register, gcc will sometimes assign the same register that was used for one of the other fixed-register operands, if it knows the values are the same. one common case is multiple zero arguments to a syscall. this horribly breaks the intended usage, which is swapping the GOT pointer from ebx into the temp register and back to perform the syscall. presumably there is a way to fix this with advanced usage of register constaints on the inline asm, but having bad memories about hellish compatibility issues with different gcc versions, for the time being i'm just going to hard-code specific registers to be used. this may hurt the compiler's ability to optimize, but it will fix serious miscompilation issues. so far the only function i know what compiled incorrectly is getrlimit.c, and naturally the bug only applies to shared (PIC) builds, but it may be more extensive and may have gone undetected.. --- arch/i386/bits/syscall.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/i386/bits/syscall.h b/arch/i386/bits/syscall.h index 1147e9f3..daea5525 100644 --- a/arch/i386/bits/syscall.h +++ b/arch/i386/bits/syscall.h @@ -61,7 +61,7 @@ static inline long __syscall1(long __n, long __a1) { unsigned long __ret; __asm__ __volatile__ ("xchg %2,%%ebx ; int $128 ; xchg %2,%%ebx" - : "=a"(__ret) : "a"(__n), "r"(__a1) : "memory"); + : "=a"(__ret) : "a"(__n), "d"(__a1) : "memory"); return __ret; } @@ -69,7 +69,7 @@ static inline long __syscall2(long __n, long __a1, long __a2) { unsigned long __ret; __asm__ __volatile__ ("xchg %2,%%ebx ; int $128 ; xchg %2,%%ebx" - : "=a"(__ret) : "a"(__n), "r"(__a1), "c"(__a2) : "memory"); + : "=a"(__ret) : "a"(__n), "d"(__a1), "c"(__a2) : "memory"); return __ret; } @@ -77,7 +77,7 @@ static inline long __syscall3(long __n, long __a1, long __a2, long __a3) { unsigned long __ret; __asm__ __volatile__ ("xchg %2,%%ebx ; int $128 ; xchg %2,%%ebx" - : "=a"(__ret) : "a"(__n), "r"(__a1), "c"(__a2), "d"(__a3) : "memory"); + : "=a"(__ret) : "a"(__n), "S"(__a1), "c"(__a2), "d"(__a3) : "memory"); return __ret; } @@ -85,7 +85,7 @@ static inline long __syscall4(long __n, long __a1, long __a2, long __a3, long __ { unsigned long __ret; __asm__ __volatile__ ("xchg %2,%%ebx ; int $128 ; xchg %2,%%ebx" - : "=a"(__ret) : "a"(__n), "r"(__a1), "c"(__a2), "d"(__a3), "S"(__a4) : "memory"); + : "=a"(__ret) : "a"(__n), "D"(__a1), "c"(__a2), "d"(__a3), "S"(__a4) : "memory"); return __ret; } -- 2.25.1