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add rcrt1 start file for fully static-linked PIE

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static-linked PIE files need startup code to relocate themselves, much
like the dynamic linker does. rcrt1.c reuses the code in dlstart.c,
stage 1 of the dynamic linker, which in turn reuses crt_arch.h, to
achieve static PIE with no new code. only relative relocations are
supported.

existing toolchains that don't yet support static PIE directly can be
repurposed by passing "-shared -Wl,-Bstatic -Wl,-Bsymbolic" instead of
"-static -pie" and substituting rcrt1.o in place of crt1.o.

all libraries being linked must be built as PIC/PIE; TEXTRELs are not
supported at this time.
This commit is contained in:
Rich Felker 2015-05-26 03:37:41 -04:00
parent ed0c824982
commit dc031ee0b1
2 changed files with 17 additions and 2 deletions
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4
Makefile
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@ -44,7 +44,7 @@ ALL_INCLUDES = $(sort $(wildcard include/*.h include/*/*.h) $(GENH) $(ARCH_INCLU
EMPTY_LIB_NAMES = m rt pthread crypt util xnet resolv dl EMPTY_LIB_NAMES = m rt pthread crypt util xnet resolv dl
EMPTY_LIBS = $(EMPTY_LIB_NAMES:%=lib/lib%.a) EMPTY_LIBS = $(EMPTY_LIB_NAMES:%=lib/lib%.a)
CRT_LIBS = lib/crt1.o lib/Scrt1.o lib/crti.o lib/crtn.o CRT_LIBS = lib/crt1.o lib/Scrt1.o lib/rcrt1.o lib/crti.o lib/crtn.o
STATIC_LIBS = lib/libc.a STATIC_LIBS = lib/libc.a
SHARED_LIBS = lib/libc.so SHARED_LIBS = lib/libc.so
TOOL_LIBS = lib/musl-gcc.specs TOOL_LIBS = lib/musl-gcc.specs
@ -89,7 +89,7 @@ src/ldso/dlstart.lo src/ldso/dynlink.lo: src/internal/dynlink.h arch/$(ARCH)/rel
crt/crt1.o crt/Scrt1.o src/ldso/dlstart.lo: $(wildcard arch/$(ARCH)/crt_arch.h) crt/crt1.o crt/Scrt1.o src/ldso/dlstart.lo: $(wildcard arch/$(ARCH)/crt_arch.h)
crt/Scrt1.o: CFLAGS += -fPIC crt/Scrt1.o crt/rcrt1.o: CFLAGS += -fPIC
OPTIMIZE_SRCS = $(wildcard $(OPTIMIZE_GLOBS:%=src/%)) OPTIMIZE_SRCS = $(wildcard $(OPTIMIZE_GLOBS:%=src/%))
$(OPTIMIZE_SRCS:%.c=%.o) $(OPTIMIZE_SRCS:%.c=%.lo): CFLAGS += -O3 $(OPTIMIZE_SRCS:%.c=%.o) $(OPTIMIZE_SRCS:%.c=%.lo): CFLAGS += -O3

15
crt/rcrt1.c Normal file
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@ -0,0 +1,15 @@
#define SHARED
#define START "_start"
#define _dlstart_c _start_c
#include "../src/ldso/dlstart.c"
int main();
void _init() __attribute__((weak));
void _fini() __attribute__((weak));
_Noreturn int __libc_start_main(int (*)(), int, char **,
void (*)(), void(*)(), void(*)());
_Noreturn void __dls2(unsigned char *base, size_t *sp)
{
__libc_start_main(main, *sp, (void *)(sp+1), _init, _fini, 0);
}