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 ATTR_LIBC_VISIBILITY;
#endif
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`
cleanup and work around visibility bug in gcc 3 that affects x86_64 in gcc 3, the visibility attribute must be placed on both the declaration and on the definition. if it's omitted from the definition, the compiler fails to emit the ".hidden" directive in the assembly, and the linker will either generate textrels (if supported, such as on i386) or refuse to link (on targets where certain types of textrels are forbidden or impossible without further assumptions about memory layout, such as on x86_64). this patch also unifies the decision about when to use visibility into libc.h and makes the visibility in the utf-8 state machine tables based on libc.h rather than a duplicate test. 2012-02-23 21:24:56 -05:00			`struct __libc __libc ATTR_LIBC_VISIBILITY;`
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`