SVC32 and SP

Carlo Caione carlo.caione at
Thu May 17 18:06:00 EDT 2012

I was debugging the problem with barebox and qemu-linaro as I
described in a previous post.
This is what I have discovered.

The problem is in the strlen function that seems to get corrupted
runtime during barebox initialization. The problem seems related to
the switch to SVC32 mode together with the __mmu_cache_flush
Before setting the cpu to SVC32 mode, the Stack Pointer is correctly
set to 0x4020fcb0, but, immediately after the writing in the cpsr
register (__asm__ __volatile__("msr cpsr, %0" : : "r"(r));) the Stack
Pointer (now R13_SVC) is in 0x40205cb0 that is in the middle of the
.text section (and precisely in the middle of the strlen routine).
The problem is that in the __mmu_cache_flush disassembly I have a huge
push {r0, r1, r2, r3, r4, r5, r6, r7, r9, r10, r11} that overwrites
the strlen function and corrupts the code.

I'm using:
arm-none-eabi-gcc (Sourcery CodeBench Lite 2011.09-69) 4.6.1
QEMU emulator version 1.0.91 (qemu-linaro from git)

Carlo Caione

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