1f925038a
YU Jincheng
2021-10-07
Subject
*: generalize "const trick"
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coreutils/test.c +2 -3include/libbb.h +25 -9libbb/appletlib.c +1 -2libbb/lineedit.c +2 -3procps/powertop.c +1 -1shell/ash.c +3 -20
coreutils/test.c+2 -3
| @@ -435,7 +435,7 @@ struct test_statics { | |
| }; | |
| /* See test_ptr_hack.c */ | |
| - | extern struct test_statics *const test_ptr_to_statics; |
| + | extern struct test_statics *BB_GLOBAL_CONST test_ptr_to_statics; |
| #define S (*test_ptr_to_statics) | |
| #define args (S.args ) | |
| @@ -446,8 +446,7 @@ extern struct test_statics *const test_ptr_to_statics; | |
| #define leaving (S.leaving ) | |
| #define INIT_S() do { \ | |
| - | (*(struct test_statics**)not_const_pp(&test_ptr_to_statics)) = xzalloc(sizeof(S)); \ |
| - | barrier(); \ |
| + | ASSIGN_CONST_PTR(test_ptr_to_statics, xzalloc(sizeof(S))); \ |
| } while (0) | |
| #define DEINIT_S() do { \ | |
| free(group_array); \ | |
include/libbb.h+25 -9
| @@ -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); \ | |
libbb/appletlib.c+1 -2
| @@ -247,8 +247,7 @@ void lbb_prepare(const char *applet | |
| IF_FEATURE_INDIVIDUAL(, char **argv)) | |
| { | |
| #ifdef bb_cached_errno_ptr | |
| - | (*(int **)not_const_pp(&bb_errno)) = get_perrno(); |
| - | barrier(); |
| + | ASSIGN_CONST_PTR(bb_errno, get_perrno()); |
| #endif | |
| applet_name = applet; | |
libbb/lineedit.c+2 -3
| @@ -192,7 +192,7 @@ struct lineedit_statics { | |
| }; | |
| /* See lineedit_ptr_hack.c */ | |
| - | extern struct lineedit_statics *const lineedit_ptr_to_statics; |
| + | extern struct lineedit_statics *BB_GLOBAL_CONST lineedit_ptr_to_statics; |
| #define S (*lineedit_ptr_to_statics) | |
| #define state (S.state ) | |
| @@ -214,8 +214,7 @@ extern struct lineedit_statics *const lineedit_ptr_to_statics; | |
| #define delbuf (S.delbuf ) | |
| #define INIT_S() do { \ | |
| - | (*(struct lineedit_statics**)not_const_pp(&lineedit_ptr_to_statics)) = xzalloc(sizeof(S)); \ |
| - | barrier(); \ |
| + | ASSIGN_CONST_PTR(lineedit_ptr_to_statics, xzalloc(sizeof(S))); \ |
| } while (0) | |
| static void deinit_S(void) | |
procps/powertop.c+1 -1
| @@ -505,7 +505,7 @@ static void cpuid(unsigned int *eax, unsigned int *ebx, unsigned int *ecx, | |
| unsigned int *edx) | |
| { | |
| /* EAX value specifies what information to return */ | |
| - | __asm__( |
| + | asm ( |
| " pushl %%ebx\n" /* Save EBX */ | |
| " cpuid\n" | |
| " movl %%ebx, %1\n" /* Save content of EBX */ | |
shell/ash.c+3 -20
| @@ -303,20 +303,6 @@ typedef long arith_t; | |
| # error "Do not even bother, ash will not run on NOMMU machine" | |
| #endif | |
| - | /* We use a trick to have more optimized code (fewer pointer reloads): |
| - | * 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 |
| - | |
| - | |
| /* ============ Hash table sizes. Configurable. */ | |
| #define VTABSIZE 39 | |
| @@ -518,8 +504,7 @@ extern struct globals_misc *BB_GLOBAL_CONST ash_ptr_to_globals_misc; | |
| #define random_gen (G_misc.random_gen ) | |
| #define backgndpid (G_misc.backgndpid ) | |
| #define INIT_G_misc() do { \ | |
| - | (*(struct globals_misc**)not_const_pp(&ash_ptr_to_globals_misc)) = xzalloc(sizeof(G_misc)); \ |
| - | barrier(); \ |
| + | ASSIGN_CONST_PTR(ash_ptr_to_globals_misc, xzalloc(sizeof(G_misc))); \ |
| savestatus = -1; \ | |
| curdir = nullstr; \ | |
| physdir = nullstr; \ | |
| @@ -1597,8 +1582,7 @@ extern struct globals_memstack *BB_GLOBAL_CONST ash_ptr_to_globals_memstack; | |
| #define g_stacknleft (G_memstack.g_stacknleft) | |
| #define stackbase (G_memstack.stackbase ) | |
| #define INIT_G_memstack() do { \ | |
| - | (*(struct globals_memstack**)not_const_pp(&ash_ptr_to_globals_memstack)) = xzalloc(sizeof(G_memstack)); \ |
| - | barrier(); \ |
| + | ASSIGN_CONST_PTR(ash_ptr_to_globals_memstack, xzalloc(sizeof(G_memstack))); \ |
| g_stackp = &stackbase; \ | |
| g_stacknxt = stackbase.space; \ | |
| g_stacknleft = MINSIZE; \ | |
| @@ -2229,8 +2213,7 @@ extern struct globals_var *BB_GLOBAL_CONST ash_ptr_to_globals_var; | |
| #endif | |
| #define INIT_G_var() do { \ | |
| unsigned i; \ | |
| - | (*(struct globals_var**)not_const_pp(&ash_ptr_to_globals_var)) = xzalloc(sizeof(G_var)); \ |
| - | barrier(); \ |
| + | ASSIGN_CONST_PTR(ash_ptr_to_globals_var, xzalloc(sizeof(G_var))); \ |
| for (i = 0; i < ARRAY_SIZE(varinit_data); i++) { \ | |
| varinit[i].flags = varinit_data[i].flags; \ | |
| varinit[i].var_text = varinit_data[i].var_text; \ | |