[PATCH] ARM: fix alignement of __bug_table section entries

Robert Jarzmik
2015-09-02T06:28:15Z

On old ARM chips, unaligned accesses to memory are not trapped and
fixed. On module load, symbols are relocated, and the relocation of
__bug_table symbols is done on a u32 basis. Yet the section is not
aligned to a multiple of 4 address, but to a multiple of 2.

This triggers an Oops on pxa architecture, where address 0xbf0021ea
is the first relocation in the __bug_table section :
apply_relocate(): pxa3xx_nand: section 13 reloc 0 sym ''
Unable to handle kernel paging request at virtual address bf0021ea
pgd = e1cd0000
[bf0021ea] *pgd=c1cce851, *pte=c1cde04f, *ppte=c1cde01f
Internal error: Oops: 23 [#1] ARM
Modules linked in:
CPU: 0 PID: 606 Comm: insmod Not tainted 4.2.0-rc8-next-20150828-cm-x300+ #887
Hardware name: CM-X300 module
task: e1c68700 ti: e1c3e000 task.ti: e1c3e000
PC is at apply_relocate+0x2f4/0x3d4
LR is at 0xbf0021ea
pc : [<c000e7c8>] lr : [<bf0021ea>] psr: 80000013
sp : e1c3fe30 ip : 60000013 fp : e49e8c60
r10: e49e8fa8 r9 : 00000000 r8 : e49e7c58
r7 : e49e8c38 r6 : e49e8a58 r5 : e49e8920 r4 : e49e8918
r3 : bf0021ea r2 : bf007034 r1 : 00000000 r0 : bf000000
Flags: Nzcv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 0000397f Table: c1cd0018 DAC: 00000051
Process insmod (pid: 606, stack limit = 0xe1c3e198)
[<c000e7c8>] (apply_relocate) from [<c005ce5c>] (load_module+0x1248/0x1f5c)
[<c005ce5c>] (load_module) from [<c005dc54>] (SyS_init_module+0xe4/0x170)
[<c005dc54>] (SyS_init_module) from [<c000a420>] (ret_fast_syscall+0x0/0x38)

Fix this by ensuring entries in __bug_table are all aligned to at least
of multiple of 4. This transforms a module section __bug_table as :
- [12] __bug_table PROGBITS 00000000 002232 000018 00 A 0 0 1
+ [12] __bug_table PROGBITS 00000000 002232 000018 00 A 0 0 4

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
---
arch/arm/include/asm/bug.h | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index b274bde24905..e7335a92144e 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -40,6 +40,7 @@ do { \
"2:\t.asciz " #__file "\n" \
".popsection\n" \
".pushsection __bug_table,\"a\"\n" \
+ ".align 2\n" \
"3:\t.word 1b, 2b\n" \
"\t.hword " #__line ", 0\n" \
".popsection"); \
--
2.1.4