73 lines
2.7 KiB
Diff
73 lines
2.7 KiB
Diff
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From 43d06ed218fc8be58987bdfd00e21e5720f0b862 Mon Sep 17 00:00:00 2001
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From: Fangrui Song <maskray@google.com>
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Date: Wed, 11 Aug 2021 09:00:37 -0700
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Subject: [PATCH] aarch64: Make elf_machine_{load_address,dynamic} robust [BZ
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#28203]
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The AArch64 ABI is largely platform agnostic and does not specify
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_GLOBAL_OFFSET_TABLE_[0] ([1]). glibc ld.so turns out to be probably the
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only user of _GLOBAL_OFFSET_TABLE_[0] and GNU ld defines the value
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to the link-time address _DYNAMIC. [2]
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In 2012, __ehdr_start was implemented in GNU ld and gold in binutils
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2.23. Using adrp+add / (-mcmodel=tiny) adr to access
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__ehdr_start/_DYNAMIC gives us a robust way to get the load address and
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the link-time address of _DYNAMIC.
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[1]: From a psABI maintainer, https://bugs.llvm.org/show_bug.cgi?id=49672#c2
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[2]: LLD's aarch64 port does not set _GLOBAL_OFFSET_TABLE_[0] to the
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link-time address _DYNAMIC.
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LLD is widely used on aarch64 Android and ChromeOS devices. Software
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just works without the need for _GLOBAL_OFFSET_TABLE_[0].
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Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
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---
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sysdeps/aarch64/dl-machine.h | 24 +++++++++---------------
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1 file changed, 9 insertions(+), 15 deletions(-)
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diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
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index d29d827..3e10cb4 100644
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--- a/sysdeps/aarch64/dl-machine.h
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+++ b/sysdeps/aarch64/dl-machine.h
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@@ -37,28 +37,22 @@ elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
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return ehdr->e_machine == EM_AARCH64;
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}
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-/* Return the link-time address of _DYNAMIC. Conveniently, this is the
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- first element of the GOT. */
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-static inline ElfW(Addr) __attribute__ ((unused))
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-elf_machine_dynamic (void)
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-{
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- extern const ElfW(Addr) _GLOBAL_OFFSET_TABLE_[] attribute_hidden;
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- return _GLOBAL_OFFSET_TABLE_[0];
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-}
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-
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/* Return the run-time load address of the shared object. */
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static inline ElfW(Addr) __attribute__ ((unused))
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elf_machine_load_address (void)
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{
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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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+ extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
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+ return (ElfW(Addr)) &__ehdr_start;
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+}
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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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+/* Return the link-time address of _DYNAMIC. */
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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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+static inline ElfW(Addr) __attribute__ ((unused))
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+elf_machine_dynamic (void)
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+{
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+ extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
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+ return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address ();
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}
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/* Set up the loaded object described by L so its unrelocated PLT
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--
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1.8.3.1
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