*: 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>

6 files changed, 34 insertions, 38 deletions

diff --git a/coreutils/test.c b/coreutils/test.c
index 7c65743..fc95672 100644
--- a/coreutils/test.c
+++ b/coreutils/test.c
@@ -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); \
diff --git a/include/libbb.h b/include/libbb.h
index dfcaa05..02cc008 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); \
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 5c5d7eb..bf26c99 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -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;
 
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index a7a3ee1..3c87abc 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -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)
diff --git a/procps/powertop.c b/procps/powertop.c
index fc6018b..24c2b32 100644
--- a/procps/powertop.c
+++ b/procps/powertop.c
@@ -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 */
diff --git a/shell/ash.c b/shell/ash.c
index 4bf0615..7b85981 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -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; \