Hello all,
I ran into a data abort in uboot during relocation (in relocate_code in relocate.S), in the "fixloop macro":
ENTRY(relocate_code)
.
/*
* fix .rel.dyn relocations
*/
ldr r2, =__rel_dyn_start /* r2 <- SRC &__rel_dyn_start */
ldr r3, =__rel_dyn_end /* r3 <- SRC &__rel_dyn_end */
fixloop:
ldmia r2!, {r0-r1} /* (r0,r1) <- (SRC location,fixup) */
and r1, r1, #0xff
cmp r1, #23 /* relative fixup? */
bne fixnext
/* relative fix: increase location by offset */
add r0, r0, r4
ldr r1, [r0] <======== DataAbort
add r1, r1, r4
str r1, [r0]
fixnext:
cmp r2, r3
blo fixloop
relocate_done:
This happened after I added some trivial code somewhere totally different and unrelated (somewhere in my board.c file, that only gets called after relocation anyway). The only thing that I can think of, is that this shifted some sections in size. Anway,
As far as I can tell, the dynamic relocation code checks if some word in that region is 23, and if so, will try to use the previous word as address (and add the relocation offset).
For some reason, r0 was zero somewhere in my case. After adding the relocation offset (of 0x18722000), the dereferencing is invalid (RAM only starts at 0x8000.0000) and causes the abort.
I now patched the code with this, and this fixes the abort for me:
diff --git a/arch/arm/lib/relocate.S b/arch/arm/lib/relocate.S
index 475d503..fba30b9 100644
--- a/arch/arm/lib/relocate.S
+++ b/arch/arm/lib/relocate.S
@@ -98,6 +98,9 @@ fixloop:
and r1, r1, #0xff
cmp r1, #23 /* relative fixup? */
bne fixnext
+ /* Check that the data is not 0. If so, skip it */
+ cmp r0, #0
+ beq fixnext
/* relative fix: increase location by offset */
add r0, r0, r4
Even though this fixes my issue, I don't understand what exactly this is trying to relocate in the first place, and what could be the relation with my seemingly unrelated change. Is this code fully ok? Or is there some edge case where the data is allowed to be zero?
Does somebody know more about this, so we can check if there is anything that really needs fixing?
Thanks for any feedback.
Kind regards,
Arnout