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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2016-07-24 14:00:13 +0200
committerWill Deacon <will.deacon@arm.com>2016-07-29 10:45:01 +0100
commit08cc55b2afd97a654f71b3bebf8bb0ec89fdc498 (patch)
tree03c1cea6bd4c4689a29c21bda065cd34336f403d /arch/arm64/Makefile
parentarm64: vmlinux.lds: make __rela_offset and __dynsym_offset ABSOLUTE (diff)
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arm64: relocatable: suppress R_AARCH64_ABS64 relocations in vmlinux
The linker routines that we rely on to produce a relocatable PIE binary treat it as a shared ELF object in some ways, i.e., it emits symbol based R_AARCH64_ABS64 relocations into the final binary since doing so would be appropriate when linking a shared library that is subject to symbol preemption. (This means that an executable can override certain symbols that are exported by a shared library it is linked with, and that the shared library *must* update all its internal references as well, and point them to the version provided by the executable.) Symbol preemption does not occur for OS hosted PIE executables, let alone for vmlinux, and so we would prefer to get rid of these symbol based relocations. This would allow us to simplify the relocation routines, and to strip the .dynsym, .dynstr and .hash sections from the binary. (Note that these are tiny, and are placed in the .init segment, but they clutter up the vmlinux binary.) Note that these R_AARCH64_ABS64 relocations are only emitted for absolute references to symbols defined in the linker script, all other relocatable quantities are covered by anonymous R_AARCH64_RELATIVE relocations that simply list the offsets to all 64-bit values in the binary that need to be fixed up based on the offset between the link time and run time addresses. Fortunately, GNU ld has a -Bsymbolic option, which is intended for shared libraries to allow them to ignore symbol preemption, and unconditionally bind all internal symbol references to its own definitions. So set it for our PIE binary as well, and get rid of the asoociated sections and the relocation code that processes them. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: fixed conflict with __dynsym_offset linker script entry] Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/Makefile')
-rw-r--r--arch/arm64/Makefile2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 393103b8abe4..76708280b04a 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -15,7 +15,7 @@ CPPFLAGS_vmlinux.lds = -DTEXT_OFFSET=$(TEXT_OFFSET)
GZFLAGS :=-9
ifneq ($(CONFIG_RELOCATABLE),)
-LDFLAGS_vmlinux += -pie
+LDFLAGS_vmlinux += -pie -Bsymbolic
endif
KBUILD_DEFCONFIG := defconfig