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[AARCH64] Rewrite elf_machine_load_address using _DYNAMIC symbol 

This patch rewrites aarch64 elf_machine_load_address to use special _DYNAMIC
symbol instead of _dl_start.

The static address of _DYNAMIC symbol is stored in the first GOT entry.
Here is the change which makes this solution work (part of binutils 2.24):
https://sourceware.org/ml/binutils/2013-06/msg00248.html

i386, x86_64 targets use the same method to do this as well.

The original implementation relies on a trick that R_AARCH64_ABS32 relocation
being resolved at link time and the static address fits in the 32bits.
However, in LP64, normally, the address is defined to be 64 bit.

Here is the C version one which should be portable in all cases.

	* sysdeps/aarch64/dl-machine.h (elf_machine_load_address): Use
	_DYNAMIC symbol to calculate load address.
This commit is contained in:
Szabolcs Nagy 2017-10-18 17:26:23 +01:00
parent 346729f66b
commit a68ba2f3cd
2 changed files with 9 additions and 33 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2017-10-18 Renlin Li <renlin.li@arm.com>
* sysdeps/aarch64/dl-machine.h (elf_machine_load_address): Use
_DYNAMIC symbol to calculate load address.
2017-10-18 Paul A. Clarke <pc@us.ibm.com> 2017-10-18 Paul A. Clarke <pc@us.ibm.com>
* sysdeps/powerpc/fpu/fenv_private.h (_FPU_MASK_TRAPS_RN): * sysdeps/powerpc/fpu/fenv_private.h (_FPU_MASK_TRAPS_RN):

37
sysdeps/aarch64/dl-machine.h
View File

@ -51,40 +51,11 @@ elf_machine_load_address (void)
/* To figure out the load address we use the definition that for any symbol: /* To figure out the load address we use the definition that for any symbol:
dynamic_addr(symbol) = static_addr(symbol) + load_addr dynamic_addr(symbol) = static_addr(symbol) + load_addr
The choice of symbol is arbitrary. The static address we obtain _DYNAMIC sysmbol is used here as its link-time address stored in
by constructing a non GOT reference to the symbol, the dynamic the special unrelocated first GOT entry. */
address of the symbol we compute using adrp/add to compute the
symbol's address relative to the PC.
This depends on 32/16bit relocations being resolved at link time
and that the static address fits in the 32/16 bits. */
ElfW(Addr) static_addr; extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
ElfW(Addr) dynamic_addr; return (ElfW(Addr)) &_DYNAMIC - elf_machine_dynamic ();
asm (" \n"
" adrp %1, _dl_start; \n"
#ifdef __LP64__
" add %1, %1, #:lo12:_dl_start \n"
#else
" add %w1, %w1, #:lo12:_dl_start \n"
#endif
" ldr %w0, 1f \n"
" b 2f \n"
"1: \n"
#ifdef __LP64__
" .word _dl_start \n"
#else
# ifdef __AARCH64EB__
" .short 0 \n"
# endif
" .short _dl_start \n"
# ifndef __AARCH64EB__
" .short 0 \n"
# endif
#endif
"2: \n"
: "=r" (static_addr), "=r" (dynamic_addr));
return dynamic_addr - static_addr;
} }
/* Set up the loaded object described by L so its unrelocated PLT /* Set up the loaded object described by L so its unrelocated PLT