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vfs: don't force a big memset of stat data just to clear padding fields

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Admittedly this is something that the compiler should be able to just do
for us, but gcc just isn't that smart.  And trying to use a structure
initializer (which would get us the right semantics) ends up resulting
in gcc allocating stack space for _two_ 'struct stat', and then copying
one into the other.

So do it by hand - just have a per-architecture macro that initializes
the padding fields.  And if the architecture doesn't provide one, fall
back to the old behavior of just doing the whole memset() first.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2012-05-06 18:02:40 -07:00
parent a52dd971f9
commit 8529f613b6
2 changed files with 31 additions and 2 deletions
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21
arch/x86/include/asm/stat.h
View file

@ -25,6 +25,12 @@ struct stat {
unsigned long __unused5;
};
/* We don't need to memset the whole thing just to initialize the padding */
#define INIT_STRUCT_STAT_PADDING(st) do { \
st.__unused4 = 0; \
st.__unused5 = 0; \
} while (0)
#define STAT64_HAS_BROKEN_ST_INO 1
/* This matches struct stat64 in glibc2.1, hence the absolutely
@ -63,6 +69,12 @@ struct stat64 {
unsigned long long st_ino;
};
/* We don't need to memset the whole thing just to initialize the padding */
#define INIT_STRUCT_STAT64_PADDING(st) do { \
memset(&st.__pad0, 0, sizeof(st.__pad0)); \
memset(&st.__pad3, 0, sizeof(st.__pad3)); \
} while (0)
#else /* __i386__ */
struct stat {
@ -87,6 +99,15 @@ struct stat {
unsigned long st_ctime_nsec;
long __unused[3];
};
/* We don't need to memset the whole thing just to initialize the padding */
#define INIT_STRUCT_STAT_PADDING(st) do { \
st.__pad0 = 0; \
st.__unused[0] = 0; \
st.__unused[1] = 0; \
st.__unused[2] = 0; \
} while (0)
#endif
/* for 32bit emulation and 32 bit kernels */

12
fs/stat.c
View file

@ -199,6 +199,10 @@ SYSCALL_DEFINE2(fstat, unsigned int, fd, struct __old_kernel_stat __user *, stat
#define valid_dev(x) choose_32_64(old_valid_dev,new_valid_dev)(x)
#define encode_dev(x) choose_32_64(old_encode_dev,new_encode_dev)(x)
#ifndef INIT_STRUCT_STAT_PADDING
# define INIT_STRUCT_STAT_PADDING(st) memset(&st, 0, sizeof(st))
#endif
static int cp_new_stat(struct kstat *stat, struct stat __user *statbuf)
{
struct stat tmp;
@ -210,7 +214,7 @@ static int cp_new_stat(struct kstat *stat, struct stat __user *statbuf)
return -EOVERFLOW;
#endif
memset(&tmp, 0, sizeof(tmp));
INIT_STRUCT_STAT_PADDING(tmp);
tmp.st_dev = encode_dev(stat->dev);
tmp.st_ino = stat->ino;
if (sizeof(tmp.st_ino) < sizeof(stat->ino) && tmp.st_ino != stat->ino)
@ -323,11 +327,15 @@ SYSCALL_DEFINE3(readlink, const char __user *, path, char __user *, buf,
/* ---------- LFS-64 ----------- */
#ifdef __ARCH_WANT_STAT64
#ifndef INIT_STRUCT_STAT64_PADDING
# define INIT_STRUCT_STAT64_PADDING(st) memset(&st, 0, sizeof(st))
#endif
static long cp_new_stat64(struct kstat *stat, struct stat64 __user *statbuf)
{
struct stat64 tmp;
memset(&tmp, 0, sizeof(struct stat64));
INIT_STRUCT_STAT64_PADDING(tmp);
#ifdef CONFIG_MIPS
/* mips has weird padding, so we don't get 64 bits there */
if (!new_valid_dev(stat->dev) || !new_valid_dev(stat->rdev))