* [2.26 COMMITTED] [AARCH64] Rewrite elf_machine_load_address using _DYNAMIC symbol
@ 2018-01-01 0:00 Aurelien Jarno
0 siblings, 0 replies; only message in thread
From: Aurelien Jarno @ 2018-01-01 0:00 UTC (permalink / raw)
To: libc-stable; +Cc: Szabolcs Nagy
From: Szabolcs Nagy <szabolcs.nagy@arm.com>
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.
(cherry picked from commit a68ba2f3cd3cbe32c1f31e13c20ed13487727b32)
---
ChangeLog | 5 +++++
sysdeps/aarch64/dl-machine.h | 39 +++++----------------------------------
2 files changed, 10 insertions(+), 34 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index d1a23a4f1b9..9f65a5cca1f 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.
+
2018-01-19 H.J. Lu <hongjiu.lu@intel.com>
[BZ #22715]
diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
index 60472036f57..3fb00e6e2d4 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
--
2.15.1
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