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*: generalize "const trick"

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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>
This commit is contained in:
YU Jincheng
2021-09-29 17:37:26 +08:00
committed by Denys Vlasenko
parent 17e6fb06b3
commit 1f925038ab
6 changed files with 34 additions and 38 deletions
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34
include/libbb.h
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@@ -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); \