diff options
| author | YU Jincheng <shana@zju.edu.cn> | 2021-09-29 12:37:26 +0300 |
|---|---|---|
| committer | Denys Vlasenko <vda.linux@googlemail.com> | 2021-10-07 16:22:35 +0300 |
| commit | 1f925038ab9c6bd8f6b3cd40ed7aab0ef10d898e (patch) | |
| tree | a625455a60081738812f469de6a02010f0c5b252 /include | |
| parent | 17e6fb06b3d36eae11575b226858e8474e2b46d3 (diff) | |
*: generalize "const trick"
While at it, change all "__asm__" to "asm"
Co-authored-by: canyie <31466456+canyie@users.noreply.github.com>
Signed-off-by: YU Jincheng <shana@zju.edu.cn>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/libbb.h | 34 |
1 files changed, 25 insertions, 9 deletions
diff --git a/include/libbb.h b/include/libbb.h index dfcaa05ec..02cc008f0 100644 --- a/include/libbb.h +++ b/include/libbb.h @@ -365,13 +365,27 @@ struct BUG_off_t_size_is_misdetected { #endif #endif +/* We use a trick to have more optimized code (fewer pointer reloads + * and reduced binary size by a few kilobytes) like: + * ash.c: extern struct globals *const ash_ptr_to_globals; + * ash_ptr_hack.c: struct globals *ash_ptr_to_globals; + * This way, compiler in ash.c knows the pointer can not change. + * + * However, this may break on weird arches or toolchains. In this case, + * set "-DBB_GLOBAL_CONST=''" in CONFIG_EXTRA_CFLAGS to disable + * this optimization. + */ +#ifndef BB_GLOBAL_CONST +# define BB_GLOBAL_CONST const +#endif + #if defined(errno) /* If errno is a define, assume it's "define errno (*__errno_location())" * and we will cache it's result in this variable */ -extern int *const bb_errno; -#undef errno -#define errno (*bb_errno) -#define bb_cached_errno_ptr 1 +extern int *BB_GLOBAL_CONST bb_errno; +# undef errno +# define errno (*bb_errno) +# define bb_cached_errno_ptr 1 #endif #if !(ULONG_MAX > 0xffffffff) @@ -2270,6 +2284,8 @@ struct globals; * If you want to assign a value, use SET_PTR_TO_GLOBALS(x) */ extern struct globals *const ptr_to_globals; +#define barrier() asm volatile ("":::"memory") + #if defined(__clang_major__) && __clang_major__ >= 9 /* Clang/llvm drops assignment to "constant" storage. Silently. * Needs serious convincing to not eliminate the store. @@ -2277,7 +2293,7 @@ extern struct globals *const ptr_to_globals; static ALWAYS_INLINE void* not_const_pp(const void *p) { void *pp; - __asm__ __volatile__( + asm volatile ( "# forget that p points to const" : /*outputs*/ "=r" (pp) : /*inputs*/ "0" (p) @@ -2288,13 +2304,13 @@ static ALWAYS_INLINE void* not_const_pp(const void *p) static ALWAYS_INLINE void* not_const_pp(const void *p) { return (void*)p; } #endif -/* At least gcc 3.4.6 on mipsel system needs optimization barrier */ -#define barrier() __asm__ __volatile__("":::"memory") -#define SET_PTR_TO_GLOBALS(x) do { \ - (*(struct globals**)not_const_pp(&ptr_to_globals)) = (void*)(x); \ +#define ASSIGN_CONST_PTR(p, v) do { \ + *(void**)not_const_pp(&p) = (void*)(v); \ + /* At least gcc 3.4.6 on mipsel needs optimization barrier */ \ barrier(); \ } while (0) +#define SET_PTR_TO_GLOBALS(x) ASSIGN_CONST_PTR(ptr_to_globals, x) #define FREE_PTR_TO_GLOBALS() do { \ if (ENABLE_FEATURE_CLEAN_UP) { \ free(ptr_to_globals); \ |