dect
/
linux-2.6
Archived
13
0
Fork 0
Code Releases Activity

[PATCH] i386: add memory clobbers to syscall macros 

As noted by matz@suse.de

The problem is, that on i386 the syscallN
macro is defined like so:

  long __res; \
  __asm__ volatile ("int $0x80" \
        : "=a" (__res) \
        : "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \
          "d" ((long)(arg3)),"S" ((long)(arg4)),"D" ((long)(arg5))); \

If one of the arguments (in the _llseek syscall it's the arg4) is a pointer
which the syscall is expected to write to (to the memory pointed to by this
ptr), then this side-effect is not captured in the asm.

If anyone uses this macro to define it's own version of the syscall
(sometimes necessary when not using glibc) and it's inlined, then GCC
doesn't know that this asm write to "*dest", when called like so for instance:

  out = 1;
  llseek (fd, bla, blubb, &out, trara)
  use (out);

Here nobody tells GCC that "out" actually is written to (just a pointer to it
is passed to the asm).  Hence GCC might (and in the above bug did)
copy-propagate "1" into the second use of "out".

The easiest solution would be to add a "memory" clobber to the definition
of this syscall macro.  As this is a syscall, it shouldn't inhibit too many
optimizations.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Andi Kleen 2005-09-12 18:49:24 +02:00 committed by Linus Torvalds
parent e92343cc8e
commit 6e44f12ba6
1 changed files with 6 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/asm-i386/unistd.h
View File

@ -332,7 +332,7 @@ type name(type1 arg1) \
long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name),"b" ((long)(arg1))); \
: "0" (__NR_##name),"b" ((long)(arg1)) : "memory"); \
__syscall_return(type,__res); \
}
@ -342,7 +342,7 @@ type name(type1 arg1,type2 arg2) \
long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2))); \
: "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)) : "memory"); \
__syscall_return(type,__res); \
}
@ -353,7 +353,7 @@ long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \
"d" ((long)(arg3))); \
"d" ((long)(arg3)) : "memory"); \
__syscall_return(type,__res); \
}
@ -364,7 +364,7 @@ long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \
"d" ((long)(arg3)),"S" ((long)(arg4))); \
"d" ((long)(arg3)),"S" ((long)(arg4)) : "memory"); \
__syscall_return(type,__res); \
}
@ -376,7 +376,7 @@ long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \
"d" ((long)(arg3)),"S" ((long)(arg4)),"D" ((long)(arg5))); \
"d" ((long)(arg3)),"S" ((long)(arg4)),"D" ((long)(arg5)) : "memory"); \
__syscall_return(type,__res); \
}
@ -389,7 +389,7 @@ __asm__ volatile ("push %%ebp ; movl %%eax,%%ebp ; movl %1,%%eax ; int $0x80 ; p
: "=a" (__res) \
: "i" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \
"d" ((long)(arg3)),"S" ((long)(arg4)),"D" ((long)(arg5)), \
"0" ((long)(arg6))); \
"0" ((long)(arg6)) : "memory"); \
__syscall_return(type,__res); \
}