Hi All,
I'm having a problem with debugging (with gdb) an application that was built
using gcc. Gcc has been patched to target a non-standard architecture, but I'm
not sure the port is complete.
When debugging with gdb, function parameters are not displayed properly. I
think this is because gdb is looking for the parameter on the stack, where in
fact it is in a register.
For example, when debugging this code:
PRIVATE uint8 u8UpdateTimeBlock(uint8 u8TimeBlock)
{
/* Update block state for next time, if in a state where regular
updates should be performed */
if ((sDemoData.sSystem.eState != E_STATE_SET_CHANNEL)
&& (sDemoData.sSystem.eState != E_STATE_SETUP_SCREEN)
&& (sDemoData.sSystem.eState != E_STATE_SCANNING))
{
u8TimeBlock++;
if (u8TimeBlock >= MAX_BLOCKS)
{
u8TimeBlock = 0;
}
}
return u8TimeBlock;
}
With gdb, it thinks that the parameter u8TimeBlock is on the stack at offset 7:
(gdb) info address u8TimeBlock
Symbol "u8TimeBlock" is an argument at offset 7.
In fact, from the disassembly listing we can see that the parameter is actually
in r3, then gets moved to r7.
04001604 <_u8UpdateTimeBlock>:
4001604: 30 21 1f b.addi r1,r1,0xfffffff8
4001607: 04 e3 b.mov r7,r3
4001609: 20 e1 e0 b.sb 0x7(r1),r7
400160c: 8c e0 75 52 00 20 b.lwz r7,0x4004aac(r0)
4001612: 40 c7 94 b.beqi r7,0x3,400163b <_u8Up
dateTimeBlock+0x37>
4001615: 8c e0 75 52 00 20 b.lwz r7,0x4004aac(r0)
400161b: 40 27 04 b.beqi r7,0x4,400163b <_u8Up
dateTimeBlock+0x37>
400161e: 8c e0 75 52 00 20 b.lwz r7,0x4004aac(r0)
4001624: 40 a7 e8 b.beqi r7,0x5,400163b <_u8Up
dateTimeBlock+0x37>
4001627: 24 e1 e0 b.lbz r7,0x7(r1)
400162a: 00 f8 b.addi r7,r7,0x1
400162c: 20 e1 e0 b.sb 0x7(r1),r7
400162f: 24 e1 e0 b.lbz r7,0x7(r1)
4001632: 3c e7 c8 b.sfleui r7,0x13
4001635: 47 26 00 b.bf 400163b <_u8UpdateTim
eBlock+0x37>
4001638: 20 01 e0 b.sb 0x7(r1),r0
400163b: 24 e1 e0 b.lbz r7,0x7(r1)
400163e: 04 67 b.mov r3,r7
4001640: 30 21 10 b.addi r1,r1,0x8
4001643: 47 d2 48 b.jr r9
I am wondering if the gcc port is somehow not putting the right debug symbol
information into the elf file.
Output of objdump -stabs:
459 FUN 0 681 04001604 25677 u8UpdateTimeBlock:f(1,8)
460 PSYM 0 680 00000007 25530 u8TimeBlock:p(1,8)
461 46 0 0 04001604 0
462 SLINE 0 681 00000000 0
463 SLINE 0 684 00000008 0
464 SLINE 0 688 00000023 0
465 SLINE 0 689 0000002b 0
466 SLINE 0 691 00000034 0
467 SLINE 0 695 00000037 0
468 SLINE 0 696 0000003a 0
469 FUN 0 0 00000042 0
470 78 0 0 04001646 0
According to http://sourceware.org/gdb/onlinedocs/stabs.html#Parameters, I
believe there should be 2 entries in the stabs for the register parameter, a
PSYM and RSYM.
Please could you tell me if this assumption is correct and if so, any ideas why
gcc would not be putting this information in the elf file? Is there any
architectural dependant code that needs to be implemented that might be missing
from the port to add this debugging information?
Thanks very much,
Matt
