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libbb: extend "errno pointer" trick to other than __GLIBC__

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Savings on musl:

function                                             old     new   delta
resume_main                                          582     614     +32
lbb_prepare                                            -      20     +20
seq_main                                             432     449     +17
fgetsetversion                                        74      88     +14
...
script_main                                         1207    1180     -27
close_silently                                        28       -     -28
shell_builtin_ulimit                                 655     626     -29
lineedit_read_key                                    280     247     -33
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 25/123 up/down: 182/-882)      Total: -700 bytes
   text	   data	    bss	    dec	    hex	filename
1005858	    551	   5676	1012085	  f7175	busybox_old
1005136	    551	   5680	1011367	  f6ea7	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2020-10-01 00:34:44 +02:00
parent 6561e07460
commit b1c7a66ca6
3 changed files with 7 additions and 6 deletions
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7
include/libbb.h
View File

@ -339,12 +339,13 @@ struct BUG_off_t_size_is_misdetected {
#endif
#endif
#if defined(__GLIBC__)
/* glibc uses __errno_location() to get a ptr to errno */
/* We can just memorize it once - no multithreading in busybox :) */
#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
#endif
#if !(ULONG_MAX > 0xffffffff)

2
libbb/appletlib.c
View File

@ -303,7 +303,7 @@ void lbb_prepare(const char *applet
void lbb_prepare(const char *applet
IF_FEATURE_INDIVIDUAL(, char **argv))
{
#ifdef __GLIBC__
#ifdef bb_cached_errno_ptr
(*(int **)not_const_pp(&bb_errno)) = __errno_location();
barrier();
#endif

4
libbb/ptr_to_globals.c
View File

@ -14,7 +14,7 @@ struct globals;
* but here we make it live in R/W memory */
struct globals *ptr_to_globals;
#ifdef __GLIBC__
#ifdef errno
int *bb_errno;
#endif
@ -27,7 +27,7 @@ int *bb_errno;
* on weird architectures, compilers, linkers and so on */
struct globals *const ptr_to_globals __attribute__ ((section (".data")));
#ifdef __GLIBC__
#ifdef errno
int *const bb_errno __attribute__ ((section (".data")));
#endif