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From: Fangrui Song <maskray@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] arm: Simplify elf_machine_{load_address,dynamic} Date: Wed, 18 Aug 2021 18:13:05 +0000 (GMT) [thread overview] Message-ID: <20210818181305.5509A3854805@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=bca0f5cbc9257c13322b99e55235c4f21ba0bd82 commit bca0f5cbc9257c13322b99e55235c4f21ba0bd82 Author: Fangrui Song <maskray@google.com> Date: Wed Aug 18 11:13:03 2021 -0700 arm: Simplify elf_machine_{load_address,dynamic} and drop reliance on _GLOBAL_OFFSET_TABLE_[0] being the link-time address of _DYNAMIC. &__ehdr_start is a better way to get the load address. This is similar to commits b37b75d269883a2c553bb7019a813094eb4e2dd1 (x86-64) and 43d06ed218fc8be58987bdfd00e21e5720f0b862 (aarch64). Reviewed-by: Joseph Myers <joseph@codesourcery.com> Diff: --- sysdeps/arm/dl-machine.h | 47 ++++++++++------------------------------------- 1 file changed, 10 insertions(+), 37 deletions(-) diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h index ff5e09e207..eb13cb8b57 100644 --- a/sysdeps/arm/dl-machine.h +++ b/sysdeps/arm/dl-machine.h @@ -37,48 +37,21 @@ elf_machine_matches_host (const Elf32_Ehdr *ehdr) return ehdr->e_machine == EM_ARM; } - -/* Return the link-time address of _DYNAMIC. Conveniently, this is the - first element of the GOT. */ -static inline Elf32_Addr __attribute__ ((unused)) -elf_machine_dynamic (void) -{ - /* Declaring this hidden ensures that a PC-relative reference is used. */ - extern const Elf32_Addr _GLOBAL_OFFSET_TABLE_[] attribute_hidden; - return _GLOBAL_OFFSET_TABLE_[0]; -} - - /* Return the run-time load address of the shared object. */ -static inline Elf32_Addr __attribute__ ((unused)) +static inline ElfW(Addr) __attribute__ ((unused)) elf_machine_load_address (void) { - Elf32_Addr pcrel_addr; -#ifdef SHARED - extern Elf32_Addr __dl_start (void *) asm ("_dl_start"); - Elf32_Addr got_addr = (Elf32_Addr) &__dl_start; - asm ("adr %0, _dl_start" : "=r" (pcrel_addr)); -#else - extern Elf32_Addr __dl_relocate_static_pie (void *) - asm ("_dl_relocate_static_pie") attribute_hidden; - Elf32_Addr got_addr = (Elf32_Addr) &__dl_relocate_static_pie; - asm ("adr %0, _dl_relocate_static_pie" : "=r" (pcrel_addr)); -#endif -#ifdef __thumb__ - /* Clear the low bit of the function address. - - NOTE: got_addr is from GOT table whose lsb is always set by linker if it's - Thumb function address. PCREL_ADDR comes from PC-relative calculation - which will finish during assembling. GAS assembler before the fix for - PR gas/21458 was not setting the lsb but does after that. Always do the - strip for both, so the code works with various combinations of glibc and - Binutils. */ - got_addr &= ~(Elf32_Addr) 1; - pcrel_addr &= ~(Elf32_Addr) 1; -#endif - return pcrel_addr - got_addr; + extern const ElfW(Ehdr) __ehdr_start attribute_hidden; + return (ElfW(Addr)) &__ehdr_start; } +/* Return the link-time address of _DYNAMIC. */ +static inline ElfW(Addr) __attribute__ ((unused)) +elf_machine_dynamic (void) +{ + extern ElfW(Dyn) _DYNAMIC[] attribute_hidden; + return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address (); +} /* Set up the loaded object described by L so its unrelocated PLT entries will jump to the on-demand fixup code in dl-runtime.c. */
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