path: root/arch/tile
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authorChris Metcalf <cmetcalf@tilera.com>2010-10-28 16:07:07 -0400
committerChris Metcalf <cmetcalf@tilera.com>2010-11-01 15:31:29 -0400
commit2c7387ef9969bb073c25ecbdcc5be30770267b16 (patch)
tree21025658ae17a84b0df346b589eb6c986c6f599d /arch/tile
parent1deb9c5dfb179819ecdbf80a1d121e26c63caab3 (diff)
asm-generic/stat.h: support 64-bit file time_t for stat()
The existing asm-generic/stat.h specifies st_mtime, etc., as a 32-value, and works well for 32-bit architectures (currently microblaze, score, and 32-bit tile). However, for 64-bit architectures it isn't sufficient to return 32 bits of time_t; this isn't good insurance against the 2037 rollover. (It also makes glibc support less convenient, since we can't use glibc's handy STAT_IS_KERNEL_STAT mode.) This change extends the two "timespec" fields for each of the three atime, mtime, and ctime fields from "int" to "long". As a result, on 32-bit platforms nothing changes, and 64-bit platforms will now work as expected. The only wrinkle is 32-bit userspace under 64-bit kernels taking advantage of COMPAT mode. For these, we leave the "struct stat64" definitions with the "int" versions of the time_t and nsec fields, so that architectures can implement compat_sys_stat64() and friends with sys_stat64(), etc., and get the expected 32-bit structure layout. This requires a field-by-field copy in the kernel, implemented by the code guarded under __ARCH_WANT_STAT64. This does mean that the shape of the "struct stat" and "struct stat64" structures is different on a 64-bit kernel, but only one of the two structures should ever be used by any given process: "struct stat" is meant for 64-bit userspace only, and "struct stat64" for 32-bit userspace only. (On a 32-bit kernel the two structures continue to have the same shape, since "long" is 32 bits.) The alternative is keeping the two structures the same shape on 64-bit kernels, which means a 64-bit time_t in "struct stat64" for 32-bit processes. This is a little unnatural since 32-bit userspace can't do anything with 64 bits of time_t information, since time_t is just "long", not "int64_t"; and in any case 32-bit userspace might expect to be running under a 32-bit kernel, which can't provide the high 32 bits anyway. In the case of a 32-bit kernel we'd then be extending the kernel's 32-bit time_t to 64 bits, then truncating it back to 32 bits again in userspace, for no particular reason. And, as mentioned above, if we have 64-bit time_t for 32-bit processes we can't easily use glibc's STAT_IS_KERNEL_STAT, since glibc's stat structure requires an embedded "struct timespec", which is a pair of "long" (32-bit) values in a 32-bit userspace. "Inventive" solutions are possible, but are pretty hacky. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com> Acked-by: Arnd Bergmann <arnd@arndb.de>
Diffstat (limited to 'arch/tile')
3 files changed, 9 insertions, 5 deletions
diff --git a/arch/tile/include/asm/stat.h b/arch/tile/include/asm/stat.h
index 3dc90fa92c7..b16e5db8f0e 100644
--- a/arch/tile/include/asm/stat.h
+++ b/arch/tile/include/asm/stat.h
@@ -1 +1,4 @@
+#define __ARCH_WANT_STAT64 /* Used for compat_sys_stat64() etc. */
#include <asm-generic/stat.h>
diff --git a/arch/tile/include/asm/unistd.h b/arch/tile/include/asm/unistd.h
index f2e3ff48533..b35c2db7119 100644
--- a/arch/tile/include/asm/unistd.h
+++ b/arch/tile/include/asm/unistd.h
@@ -41,6 +41,7 @@ __SYSCALL(__NR_cmpxchg_badaddr, sys_cmpxchg_badaddr)
#endif /* _ASM_TILE_UNISTD_H */
diff --git a/arch/tile/kernel/compat.c b/arch/tile/kernel/compat.c
index 77739cdd946..67617a05e60 100644
--- a/arch/tile/kernel/compat.c
+++ b/arch/tile/kernel/compat.c
@@ -148,11 +148,11 @@ long tile_compat_sys_msgrcv(int msqid,
#define compat_sys_readahead sys32_readahead
#define compat_sys_sync_file_range compat_sys_sync_file_range2
-/* The native 64-bit "struct stat" matches the 32-bit "struct stat64". */
-#define compat_sys_stat64 sys_newstat
-#define compat_sys_lstat64 sys_newlstat
-#define compat_sys_fstat64 sys_newfstat
-#define compat_sys_fstatat64 sys_newfstatat
+/* We leverage the "struct stat64" type for 32-bit time_t/nsec. */
+#define compat_sys_stat64 sys_stat64
+#define compat_sys_lstat64 sys_lstat64
+#define compat_sys_fstat64 sys_fstat64
+#define compat_sys_fstatat64 sys_fstatat64
/* The native sys_ptrace dynamically handles compat binaries. */
#define compat_sys_ptrace sys_ptrace