mirrors/musl
1
0
Fork 0
mirror of https://git.musl-libc.org/git/musl synced 2025-02-20 20:24:28 +03:00
Code Issues Packages Projects Releases Wiki Activity

bypass indirection through pointer objects to access stdin/out/err

Browse Source 
by ABI, the public stdin/out/err macros use extern pointer objects,
and this is necessary to avoid copy relocations that would be
expensive and make the size of the FILE structure part of the ABI.
however, internally it makes sense to access the underlying FILE
objects directly. this avoids both an indirection through the GOT to
find the address of the stdin/out/err pointer objects (which can't be
computed PC-relative because they may have been moved to the main
program by copy relocations) and an indirection through the resulting
pointer object.

in most places this is just a minor optimization, but in the case of
getchar and putchar (and the unlocked versions thereof), ipa constant
propagation makes all accesses to members of stdin/out PC-relative or
GOT-relative, possibly reducing register pressure as well.
This commit is contained in:
Rich Felker 2018-10-17 23:57:28 -04:00
parent d664061adb
commit d8f2efa708
4 changed files with 33 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
src/include/stdio.h Normal file
View File

@ -0,0 +1,18 @@
#ifndef STDIO_H
#define STDIO_H
#include "../../include/stdio.h"
#undef stdin
#undef stdout
#undef stderr
extern hidden FILE __stdin_FILE;
extern hidden FILE __stdout_FILE;
extern hidden FILE __stderr_FILE;
#define stdin (&__stdin_FILE)
#define stdout (&__stdout_FILE)
#define stderr (&__stderr_FILE)
#endif

8
src/stdio/stderr.c
View File

@ -1,7 +1,9 @@
#include "stdio_impl.h"
#undef stderr
static unsigned char buf[UNGET];
static FILE f = {
hidden FILE __stderr_FILE = {
.buf = buf+UNGET,
.buf_size = 0,
.fd = 2,
@ -12,5 +14,5 @@ static FILE f = {
.close = __stdio_close,
.lock = -1,
};
FILE *const stderr = &f;
FILE *volatile __stderr_used = &f;
FILE *const stderr = &__stderr_FILE;
FILE *volatile __stderr_used = &__stderr_FILE;

8
src/stdio/stdin.c
View File

@ -1,7 +1,9 @@
#include "stdio_impl.h"
#undef stdin
static unsigned char buf[BUFSIZ+UNGET];
static FILE f = {
hidden FILE __stdin_FILE = {
.buf = buf+UNGET,
.buf_size = sizeof buf-UNGET,
.fd = 0,
@ -11,5 +13,5 @@ static FILE f = {
.close = __stdio_close,
.lock = -1,
};
FILE *const stdin = &f;
FILE *volatile __stdin_used = &f;
FILE *const stdin = &__stdin_FILE;
FILE *volatile __stdin_used = &__stdin_FILE;

8
src/stdio/stdout.c
View File

@ -1,7 +1,9 @@
#include "stdio_impl.h"
#undef stdout
static unsigned char buf[BUFSIZ+UNGET];
static FILE f = {
hidden FILE __stdout_FILE = {
.buf = buf+UNGET,
.buf_size = sizeof buf-UNGET,
.fd = 1,
@ -12,5 +14,5 @@ static FILE f = {
.close = __stdio_close,
.lock = -1,
};
FILE *const stdout = &f;
FILE *volatile __stdout_used = &f;
FILE *const stdout = &__stdout_FILE;
FILE *volatile __stdout_used = &__stdout_FILE;