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author | H.J. Lu <hjl.tools@gmail.com> | 2016-03-16 20:04:35 -0700 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-10-20 10:00:47 +0200 |
commit | 74a2862d963e1e84616c3c9feeda1caed9f72c19 (patch) | |
tree | 1b752dcb661bb3dd6574c5d6df9c028651843641 /include/linux/mm.h | |
parent | 6c789d9eddab3bff59e89aa6f2723b1ff652fed9 (diff) | |
download | linux-stable-74a2862d963e1e84616c3c9feeda1caed9f72c19.tar.gz linux-stable-74a2862d963e1e84616c3c9feeda1caed9f72c19.tar.bz2 linux-stable-74a2862d963e1e84616c3c9feeda1caed9f72c19.zip |
x86/build: Build compressed x86 kernels as PIE
commit 6d92bc9d483aa1751755a66fee8fb39dffb088c0 upstream.
The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X
relocation to get the symbol address in PIC. When the compressed x86
kernel isn't built as PIC, the linker optimizes R_386_GOT32X relocations
to their fixed symbol addresses. However, when the compressed x86
kernel is loaded at a different address, it leads to the following
load failure:
Failed to allocate space for phdrs
during the decompression stage.
If the compressed x86 kernel is relocatable at run-time, it should be
compiled with -fPIE, instead of -fPIC, if possible and should be built as
Position Independent Executable (PIE) so that linker won't optimize
R_386_GOT32X relocation to its fixed symbol address.
Older linkers generate R_386_32 relocations against locally defined
symbols, _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less
optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
R_386_32 relocations when relocating the kernel. To generate
R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as
hidden in both 32-bit and 64-bit x86 kernels.
To build a 64-bit compressed x86 kernel as PIE, we need to disable the
relocation overflow check to avoid relocation overflow errors. We do
this with a new linker command-line option, -z noreloc-overflow, which
got added recently:
commit 4c10bbaa0912742322f10d9d5bb630ba4e15dfa7
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Tue Mar 15 11:07:06 2016 -0700
Add -z noreloc-overflow option to x86-64 ld
Add -z noreloc-overflow command-line option to the x86-64 ELF linker to
disable relocation overflow check. This can be used to avoid relocation
overflow check if there will be no dynamic relocation overflow at
run-time.
The 64-bit compressed x86 kernel is built as PIE only if the linker supports
-z noreloc-overflow. So far 64-bit relocatable compressed x86 kernel
boots fine even when it is built as a normal executable.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
[ Edited the changelog and comments. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/mm.h')
0 files changed, 0 insertions, 0 deletions