fix possible clobbering of syscall return values on mips

depending on the compiler's interpretation of __asm__ register names
for register class objects, it may be possible for the return value in
r2 to be clobbered by the function call to __stat_fix. I have not
observed any such breakage in normal builds and suspect it only
happens with -O0 or other unusual build options, but since there's an
ambiguity as to the semantics of this feature, it's best to use an
explicit temporary to avoid the issue.

based on reporting and patch by Eugene.

diff --git a/arch/mips/syscall_arch.h b/arch/mips/syscall_arch.h
index 0f89a1c1e31c60bf14862c6f83c061df9a2966cf..69b8154f259c8c245f4860def6e42d6098e4f268 100644 (file)
--- a/arch/mips/syscall_arch.h
+++ b/arch/mips/syscall_arch.h
@@ -60,8 +60,9 @@ static inline long __syscall2(long n, long a, long b)
                : "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
                  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
        if (r7) return -r2;
+       long ret = r2;
        if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
-       return r2;
+       return ret;
 }
 
 static inline long __syscall3(long n, long a, long b, long c)
@@ -78,8 +79,9 @@ static inline long __syscall3(long n, long a, long b, long c)
                : "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
                  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
        if (r7) return -r2;
+       long ret = r2;
        if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
-       return r2;
+       return ret;
 }
 
 static inline long __syscall4(long n, long a, long b, long c, long d)
@@ -96,9 +98,10 @@ static inline long __syscall4(long n, long a, long b, long c, long d)
                : "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
                  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
        if (r7) return -r2;
+       long ret = r2;
        if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
        if (n == SYS_fstatat) __stat_fix(c);
-       return r2;
+       return ret;
 }
 
 #else