musl - musl - an implementation of the standard library for Linux-based systems

musl - an implementation of the standard library for Linux-based systems

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author	Rich Felker <dalias@aerifal.cx>	2012年04月04日 00:37:33 -0400
committer	Rich Felker <dalias@aerifal.cx>	2012年04月04日 00:37:33 -0400
commit	5bd0ab8af66829af74ed80cac767ce1c041fd767 (patch)
tree	0e4c9ae49ee2aea74348ae866a2cdb0197ce2315
parent	450f2c4a8515f2c5c9f469082bf69fdef009d26a (diff)
download	musl-5bd0ab8af66829af74ed80cac767ce1c041fd767.tar.gz

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..

Diffstat

-rw-r--r--

arch/i386/bits/syscall.h

1 files 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ドル ; 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ドル ; 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ドル ; 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ドル ; 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;

}

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