From 02e541db0540a2830f4af749c6f2b650abbbb77c Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Wed, 25 Mar 2015 07:37:57 +0100 Subject: [PATCH] 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 Signed-off-by: Ard Biesheuvel Signed-off-by: Russell King --- arch/arm/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) 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 -- 2.20.1