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| author | Ard Biesheuvel <ard.biesheuvel@linaro.org> | 2015-03-25 09:37:57 +0300 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2015-03-30 01:11:56 +0300 |
| commit | 02e541db0540a2830f4af749c6f2b650abbbb77c (patch) | |
| tree | 76c635fc3fa34cb652f8800b8815aebd3ad6da5a /arch/arm/Makefile | |
| parent | c4a84ae39b4a5bdf609c0001e14207aa731aab30 (diff) | |
| download | linux-02e541db0540a2830f4af749c6f2b650abbbb77c.tar.xz | |
ARM: 8323/1: force linker to use PIC veneers
When building a very large kernel, it is up to the linker to decide
when and where to insert stubs to allow calls to functions that are
out of range for the ordinary b/bl instructions.
However, since the kernel is built as a position dependent binary,
these stubs (aka veneers) may contain absolute addresses, which will
break far calls performed with the MMU off.
For instance, the call from __enable_mmu() in the .head.text section
to __turn_mmu_on() in the .idmap.text section may be turned into
something like this:
c0008168 <__enable_mmu>:
c0008168: f020 0002 bic.w r0, r0, #2
c000816c: f420 5080 bic.w r0, r0, #4096
c0008170: f000 b846 b.w c0008200 <____turn_mmu_on_veneer>
[...]
c0008200 <____turn_mmu_on_veneer>:
c0008200: 4778 bx pc
c0008202: 46c0 nop
c0008204: e59fc000 ldr ip, [pc]
c0008208: e12fff1c bx ip
c000820c: c13dfae1 teqgt sp, r1, ror #21
[...]
c13dfae0 <__turn_mmu_on>:
c13dfae0: 4600 mov r0, r0
[...]
After adding --pic-veneer to the LDFLAGS, the veneer is emitted like
this instead:
c0008200 <____turn_mmu_on_veneer>:
c0008200: 4778 bx pc
c0008202: 46c0 nop
c0008204: e59fc004 ldr ip, [pc, #4]
c0008208: e08fc00c add ip, pc, ip
c000820c: e12fff1c bx ip
c0008210: 013d7d31 teqeq sp, r1, lsr sp
c0008214: 00000000 andeq r0, r0, r0
Note that this particular example is best addressed by moving
.head.text and .idmap.text closer together, but this issue could
potentially affect any code that needs to execute with the
MMU off.
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/Makefile')
| -rw-r--r-- | arch/arm/Makefile | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm/Makefile b/arch/arm/Makefile index 7f99cd652203..7d980706bfb4 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -13,7 +13,7 @@ # Ensure linker flags are correct LDFLAGS := -LDFLAGS_vmlinux :=-p --no-undefined -X +LDFLAGS_vmlinux :=-p --no-undefined -X --pic-veneer ifeq ($(CONFIG_CPU_ENDIAN_BE8),y) LDFLAGS_vmlinux += --be8 LDFLAGS_MODULE += --be8 |