musl/src/internal/libc.c

#include "libc.h"

#ifdef USE_LIBC_ACCESSOR
struct __libc *__libc_loc()
{
	static struct __libc __libc;
	return &__libc;
}
#else
struct __libc __libc;
#endif

#ifdef BROKEN_VISIBILITY
__asm__(".hidden __libc");
#endif

size_t __hwcap;
size_t __sysinfo;
initial check-in, version 0.5.0 2011-02-12 00:22:29 -05:00			`#include "libc.h"`

various changes in preparation for dynamic linking support prefer using visibility=hidden for __libc internal data, rather than an accessor function, if the compiler has visibility. optimize with -O3 for PIC targets (shared library). without heavy inlining, reloading the GOT register in small functions kills performance. 20-30% size increase for a single libc.so is not a big deal, compared to comparaible size increase in every static binaries. use -Bsymbolic-functions, not -Bsymbolic. global variables are subject to COPY relocations, and thus binding their addresses in the library at link time will cause library functions to read the wrong (original) copies instead of the copies made in the main program's bss section. add entry point, _start, for dynamic linker. 2011-02-24 16:37:21 -05:00			`#ifdef USE_LIBC_ACCESSOR`
use an accessor function for __libc data pointer when compiled as PIC prior to this change, a large portion of libc was unusable prior to relocation by the dynamic linker, due to dependence on the global data in the __libc structure and the need to obtain its address through the GOT. with this patch, the accessor function __libc_loc is now able to obtain the address of __libc via PC-relative addressing without using the GOT. this means the majority of libc functionality is now accessible right away. naturally, the above statements all depend on having an architecture where PC-relative addressing and jumps/calls are feasible, and a compiler that generates the appropriate code. 2011-02-20 22:30:06 -05:00			`struct __libc *__libc_loc()`
			`{`
			`static struct __libc __libc;`
			`return &__libc;`
			`}`
			`#else`
remove useless attribute visibility from definitions this was a failed attempt at working around the gcc 3 visibility bug affecting x86_64. subsequent patch will address it with an ugly but working hack. 2012-02-24 20:02:42 -05:00			`struct __libc __libc;`
use an accessor function for __libc data pointer when compiled as PIC prior to this change, a large portion of libc was unusable prior to relocation by the dynamic linker, due to dependence on the global data in the __libc structure and the need to obtain its address through the GOT. with this patch, the accessor function __libc_loc is now able to obtain the address of __libc via PC-relative addressing without using the GOT. this means the majority of libc functionality is now accessible right away. naturally, the above statements all depend on having an architecture where PC-relative addressing and jumps/calls are feasible, and a compiler that generates the appropriate code. 2011-02-20 22:30:06 -05:00			`#endif`
new attempt at working around the gcc 3 visibility bug since gcc is failing to generate the necessary ".hidden" directive in the output asm, generate it explicitly with an __asm__ statement... 2012-02-24 20:07:21 -05:00
			`#ifdef BROKEN_VISIBILITY`
			`__asm__(".hidden __libc");`
			`#endif`
save AT_HWCAP from auxv for subsequent use in machine-specific code it's expected that this will be needed/useful only in asm, so I've given it its own symbol that can be addressed in pc-relative ways from asm rather than adding a field in the __libc structure which would require hard-coding the offset wherever it's used. 2012-07-27 00:14:57 -04:00
			`size_t __hwcap;`
i386 vsyscall support (vdso-provided sysenter/syscall instruction based) this doubles the performance of the fastest syscalls on the atom I tested it on; improvement is reportedly much more dramatic on worst-case cpus. cannot be used for cancellable syscalls. 2012-10-11 22:47:07 -04:00			`size_t __sysinfo;`