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| author | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2017-10-18 17:26:23 +0100 |
|---|---|---|
| committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2017-10-18 17:35:16 +0100 |
| commit | a68ba2f3cd3cbe32c1f31e13c20ed13487727b32 (patch) | |
| tree | 41490ad1d5dd26a7fd4d4b0990c560158a3e9a44 | |
| parent | 346729f66b905344e4ce24045489d189e5b4a9b8 (diff) | |
| download | glibc-a68ba2f3cd3cbe32c1f31e13c20ed13487727b32.tar.gz glibc-a68ba2f3cd3cbe32c1f31e13c20ed13487727b32.tar.xz glibc-a68ba2f3cd3cbe32c1f31e13c20ed13487727b32.zip | |
[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.
| -rw-r--r-- | ChangeLog | 5 | ||||
| -rw-r--r-- | sysdeps/aarch64/dl-machine.h | 39 |
2 files changed, 10 insertions, 34 deletions
diff --git a/ChangeLog b/ChangeLog index a34405285f..eae1159cf3 100644 --- a/ChangeLog +++ b/ChangeLog @@ -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> * 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 b1245476dc..e7656129f5 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 |