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76 lines
2.7 KiB
Diff
76 lines
2.7 KiB
Diff
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commit a68ba2f3cd3cbe32c1f31e13c20ed13487727b32
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Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
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Date: Wed Oct 18 17:26:23 2017 +0100
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[AARCH64] Rewrite elf_machine_load_address using _DYNAMIC symbol
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This patch rewrites aarch64 elf_machine_load_address to use special _DYNAMIC
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symbol instead of _dl_start.
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The static address of _DYNAMIC symbol is stored in the first GOT entry.
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Here is the change which makes this solution work (part of binutils 2.24):
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https://sourceware.org/ml/binutils/2013-06/msg00248.html
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i386, x86_64 targets use the same method to do this as well.
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The original implementation relies on a trick that R_AARCH64_ABS32 relocation
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being resolved at link time and the static address fits in the 32bits.
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However, in LP64, normally, the address is defined to be 64 bit.
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Here is the C version one which should be portable in all cases.
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* sysdeps/aarch64/dl-machine.h (elf_machine_load_address): Use
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_DYNAMIC symbol to calculate load address.
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---
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sysdeps/aarch64/dl-machine.h | 37 ++++---------------------------------
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1 file changed, 4 insertions(+), 33 deletions(-)
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--- a/sysdeps/aarch64/dl-machine.h
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+++ b/sysdeps/aarch64/dl-machine.h
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@@ -51,40 +51,11 @@
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/* To figure out the load address we use the definition that for any symbol:
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dynamic_addr(symbol) = static_addr(symbol) + load_addr
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- The choice of symbol is arbitrary. The static address we obtain
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- by constructing a non GOT reference to the symbol, the dynamic
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- address of the symbol we compute using adrp/add to compute the
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- symbol's address relative to the PC.
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- This depends on 32/16bit relocations being resolved at link time
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- and that the static address fits in the 32/16 bits. */
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+ _DYNAMIC sysmbol is used here as its link-time address stored in
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+ the special unrelocated first GOT entry. */
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- ElfW(Addr) static_addr;
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- ElfW(Addr) dynamic_addr;
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-
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- asm (" \n"
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-" adrp %1, _dl_start; \n"
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-#ifdef __LP64__
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-" add %1, %1, #:lo12:_dl_start \n"
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-#else
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-" add %w1, %w1, #:lo12:_dl_start \n"
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-#endif
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-" ldr %w0, 1f \n"
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-" b 2f \n"
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-"1: \n"
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-#ifdef __LP64__
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-" .word _dl_start \n"
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-#else
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-# ifdef __AARCH64EB__
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-" .short 0 \n"
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-# endif
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-" .short _dl_start \n"
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-# ifndef __AARCH64EB__
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-" .short 0 \n"
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-# endif
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-#endif
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-"2: \n"
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- : "=r" (static_addr), "=r" (dynamic_addr));
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- return dynamic_addr - static_addr;
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+ extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
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+ return (ElfW(Addr)) &_DYNAMIC - elf_machine_dynamic ();
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}
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/* Set up the loaded object described by L so its unrelocated PLT
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