jyapayne/musl
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

use explicit visibility to optimize a few hot-path function calls

Browse source 
on x86 and some other archs, functions which make function calls which
might go through a PLT incur a significant overhead cost loading the
GOT register prior to making the call. this load is utterly useless in
musl, since all calls are bound at library-creation time using
-Bsymbolic-functions, but the compiler has no way of knowing this, and
attempts to set the default visibility to protected have failed due to
bugs in GCC and binutils.

this commit simply manually assigns hidden/protected visibility, as
appropriate, to a few internal-use-only functions which have many
callers, or which have callers that are hot paths like getc/putc. it
shaves about 5k off the i386 libc.so with -Os. many of the
improvements are in syscall wrappers, where the benefit is just size
and performance improvement is unmeasurable noise amid the syscall
overhead. however, stdio may be measurably faster.

if in the future there are toolchains that can do the same thing
globally without introducing linking bugs, it might be worth
considering removing these workarounds.
This commit is contained in:
Rich Felker 2012-10-25 15:40:58 -04:00
commit 607b05aca6
3 changed files with 13 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

8
src/internal/stdio_impl.h
View file

@ -74,10 +74,10 @@ size_t __string_read(FILE *, unsigned char *, size_t);
int __toread(FILE *);
int __towrite(FILE *);
int __overflow(FILE *, int);
int __oflow(FILE *);
int __uflow(FILE *);
int __underflow(FILE *);
#if defined(__PIC__) && (100*__GNUC__+__GNUC_MINOR__ >= 303)
__attribute__((visibility("protected")))
#endif
int __overflow(FILE *, int), __uflow(FILE *);
int __fseeko(FILE *, off_t, int);
int __fseeko_unlocked(FILE *, off_t, int);