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authorRich Felker <dalias@aerifal.cx>2015-04-13 02:56:26 -0400
committerRich Felker <dalias@aerifal.cx>2015-04-13 03:04:42 -0400
commitf3ddd173806fd5c60b3f034528ca24542aecc5b9 (patch)
tree63cc7432a3c40f011c4818de32ef6257acbf0e73 /arch/aarch64
parent385c01112c083eb383d972da45836d497cc0556d (diff)
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dynamic linker bootstrap overhaul
this overhaul further reduces the amount of arch-specific code needed by the dynamic linker and removes a number of assumptions, including: - that symbolic function references inside libc are bound at link time via the linker option -Bsymbolic-functions. - that libc functions used by the dynamic linker do not require access to data symbols. - that static/internal function calls and data accesses can be made without performing any relocations, or that arch-specific startup code handled any such relocations needed. removing these assumptions paves the way for allowing libc.so itself to be built with stack protector (among other things), and is achieved by a three-stage bootstrap process: 1. relative relocations are processed with a flat function. 2. symbolic relocations are processed with no external calls/data. 3. main program and dependency libs are processed with a fully-functional libc/ldso. reduction in arch-specific code is achived through the following: - crt_arch.h, used for generating crt1.o, now provides the entry point for the dynamic linker too. - asm is no longer responsible for skipping the beginning of argv[] when ldso is invoked as a command. - the functionality previously provided by __reloc_self for heavily GOT-dependent RISC archs is now the arch-agnostic stage-1. - arch-specific relocation type codes are mapped directly as macros rather than via an inline translation function/switch statement.
Diffstat (limited to 'arch/aarch64')
-rw-r--r--arch/aarch64/crt_arch.h13
-rw-r--r--arch/aarch64/reloc.h38
2 files changed, 21 insertions, 30 deletions
diff --git a/arch/aarch64/crt_arch.h b/arch/aarch64/crt_arch.h
index 32066881..3a4b321e 100644
--- a/arch/aarch64/crt_arch.h
+++ b/arch/aarch64/crt_arch.h
@@ -1,9 +1,14 @@
__asm__(
-".global _start\n"
-".type _start,%function\n"
-"_start:\n"
+".global " START "\n"
+".type " START ",%function\n"
+START ":\n"
" mov x29, #0\n"
" mov x30, #0\n"
" mov x0, sp\n"
+".weak _DYNAMIC\n"
+".hidden _DYNAMIC\n"
+" adrp x1, _DYNAMIC\n"
+" add x1, x1, #:lo12:_DYNAMIC\n"
" and sp, x0, #-16\n"
-" b __cstart\n");
+" b " START "_c\n"
+);
diff --git a/arch/aarch64/reloc.h b/arch/aarch64/reloc.h
index e95ae9a8..1b0402bc 100644
--- a/arch/aarch64/reloc.h
+++ b/arch/aarch64/reloc.h
@@ -1,5 +1,3 @@
-#include <string.h>
-#include <elf.h>
#include <endian.h>
#if __BYTE_ORDER == __BIG_ENDIAN
@@ -14,27 +12,15 @@
#define TPOFF_K 16
-static int remap_rel(int type)
-{
- switch(type) {
- case R_AARCH64_ABS64:
- return REL_SYMBOLIC;
- case R_AARCH64_GLOB_DAT:
- return REL_GOT;
- case R_AARCH64_JUMP_SLOT:
- return REL_PLT;
- case R_AARCH64_RELATIVE:
- return REL_RELATIVE;
- case R_AARCH64_COPY:
- return REL_COPY;
- case R_AARCH64_TLS_DTPMOD64:
- return REL_DTPMOD;
- case R_AARCH64_TLS_DTPREL64:
- return REL_DTPOFF;
- case R_AARCH64_TLS_TPREL64:
- return REL_TPOFF;
- case R_AARCH64_TLSDESC:
- return REL_TLSDESC;
- }
- return 0;
-}
+#define REL_SYMBOLIC R_AARCH64_ABS64
+#define REL_GOT R_AARCH64_GLOB_DAT
+#define REL_PLT R_AARCH64_JUMP_SLOT
+#define REL_RELATIVE R_AARCH64_RELATIVE
+#define REL_COPY R_AARCH64_COPY
+#define REL_DTPMOD R_AARCH64_TLS_DTPMOD64
+#define REL_DTPOFF R_AARCH64_TLS_DTPREL64
+#define REL_TPOFF R_AARCH64_TLS_TPREL64
+#define REL_TLSDESC R_AARCH64_TLSDESC
+
+#define CRTJMP(pc,sp) __asm__ __volatile__( \
+ "mov sp,%1 ; bx %0" : : "r"(pc), "r"(sp) : "memory" )