From a68ba2f3cd3cbe32c1f31e13c20ed13487727b32 Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Wed, 18 Oct 2017 17:26:23 +0100 Subject: [PATCH] [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. --- ChangeLog | 5 +++++ sysdeps/aarch64/dl-machine.h | 39 +++++---------------------------------- 2 files changed, 10 insertions(+), 34 deletions(-) diff --git a/ChangeLog b/ChangeLog index a344052..eae1159 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,8 @@ +2017-10-18 Renlin Li + + * sysdeps/aarch64/dl-machine.h (elf_machine_load_address): Use + _DYNAMIC symbol to calculate load address. + 2017-10-18 Paul A. Clarke * sysdeps/powerpc/fpu/fenv_private.h (_FPU_MASK_TRAPS_RN): diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h index b124547..e765612 100644 --- a/sysdeps/aarch64/dl-machine.h +++ b/sysdeps/aarch64/dl-machine.h @@ -51,40 +51,11 @@ elf_machine_load_address (void) /* To figure out the load address we use the definition that for any symbol: dynamic_addr(symbol) = static_addr(symbol) + load_addr - The choice of symbol is arbitrary. The static address we obtain - by constructing a non GOT reference to the symbol, the dynamic - 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; - ElfW(Addr) dynamic_addr; - - 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; + _DYNAMIC sysmbol is used here as its link-time address stored in + the special unrelocated first GOT entry. */ + + extern ElfW(Dyn) _DYNAMIC[] attribute_hidden; + return (ElfW(Addr)) &_DYNAMIC - elf_machine_dynamic (); } /* Set up the loaded object described by L so its unrelocated PLT -- 2.7.4