http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53016
Bug #: 53016
Summary: memcpy optimization can cause unaligned access on ARM
Classification: Unclassified
Product: gcc
Version: 4.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: jquesne...@gmail.com
Created attachment 27174
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27174
reproduction files
The built-in memcpy that -O2 substitutes in seems to cause an unaligned memory
access on ARMv5TE when structs are stacked in a certain way. I originally
discovered this when a release build of native code for inclusion in an Android
program caused a SIGBUS. Attached is a simple test case that replicates this on
Android. There is no main() function but it should be trivial to substitute in
(sorry, I don't have access to a regular ARM Linux box). It appears to involve
over-aggressive use of ldm/stm (possibly ignoring padding?).
Works fine (-O0):
memcpy((void*)&parent.children[2],(const void*)child3,size);
24: 4b0a ldr r3, [pc, #40]
26: 447b add r3, pc
28: 1c19 adds r1, r3, #0
2a: 3138 adds r1, #56
2c: 4b09 ldr r3, [pc, #36]
2e: 447b add r3, pc
30: 681b ldr r3, [r3, #0]
32: 9a03 ldr r2, [sp, #12]
34: 1c08 adds r0, r1, #0
36: 1c11 adds r1, r2, #0
38: 1c1a adds r2, r3, #0
3a: f7ff fffe bl 0 <memcpy>
Gives SIGBUS (-O2):
memcpy((void*)&parent.children[2],(const void*)child3,size);
2: 4b07 ldr r3, [pc, #28]
4: 4907 ldr r1, [pc, #28]
6: 447b add r3, pc
8: 681a ldr r2, [r3, #0]
a: 4479 add r1, pc
c: 3138 adds r1, #56
e: 1c0b adds r3, r1, #0
10: 323c adds r2, #60
12: ca31 ldmia r2!, {r0, r4, r5} <--- Unaligned access
14: c331 stmia r3!, {r0, r4, r5}
16: ca13 ldmia r2!, {r0, r1, r4}
18: c313 stmia r3!, {r0, r1, r4}
1a: 6812 ldr r2, [r2, #0]
1c: 601a str r2, [r3, #0]
I have confirmed this both on a TI OMAP 3530 (BeagleBoard) and Samsung Exynos
3110 (Samsung Epic 4G). I'm not sure if this is the same as bug #47754.
