Gdb skips lines of source code when debugging assembler program for ARM7 microcontroller

Question

I have a problem debugging a simple program written in assembly language for the ARM7 microcontroller (AT91SAM7S64). I use gcc, gdb and OpenOCD. My program is loaded for the correct setting of the target and works fine (the LED blinks). But gdb skips certain lines of source code when I invoke the "next" command.

Here is a snippet of source code:

Reset_Handler: LDR R0, =0x0100 LDR R1, =PIOA_PER STR R0, [R1] LDR R1, =PIOA_OER STR R0, [R1] uuu: bl wait; LDR R1, =PIOA_SODR STR R0, [R1] uuu1: bl wait; LDR R2, =PIOA_CODR STR R0, [R2] b uuu; @ one second delay wait: ............. ............. .end 

To get gdb output (see below), I used the "target sim" instead of the real target, but rusults is the same.

 (gdb) target sim Connected to the simulator. (gdb) load Loading section .text, size 0xc8 vma 0x100000 Start address 0x100000 Transfer rate: 1600 bits in <1 sec. (gdb) b Reset_Handler Breakpoint 1 at 0x100064: file main.s, line 59. (gdb) run Starting program: C:\Arm\Projects\Asm/./main.elf Breakpoint 1, Reset_Handler () at main.s:60 60 LDR R1, =PIOA_PER (gdb) n 61 STR R0, [R1] (gdb) n 63 LDR R1, =PIOA_OER (gdb) n 64 STR R0, [R1] (gdb) n uuu () at main.s:66 66 bl wait; (gdb) n 67 LDR R1, =PIOA_SODR (gdb) n 68 STR R0, [R1] (gdb) n <<<<<--------- Here the problem begins 67 LDR R1, =PIOA_SODR (gdb) n 68 STR R0, [R1] (gdb) n 67 LDR R1, =PIOA_SODR (gdb) n 68 STR R0, [R1] (gdb) stepi <<<<<------ Doing a 'stepi' command allows to pass below 'uuu1' label uuu1 () at main.s:70 70 bl wait; (gdb) n 71 LDR R2, =PIOA_CODR (gdb) n 72 STR R0, [R2] (gdb) n 73 b uuu; (gdb) n <<<<<--------- Here the problem begins again 71 LDR R2, =PIOA_CODR (gdb) n 72 STR R0, [R2] (gdb) n 73 b uuu; (gdb) n 71 LDR R2, =PIOA_CODR (gdb) where #0 uuu1 () at main.s:71 #1 0x00100084 in uuu1 () at main.s:70 Backtrace stopped: previous frame identical to this frame (corrupt stack?) (gdb) 

Gdb seems to suggest "uuu1" as a separate function and skips it for some reason. If I remove the label "uuu1", the problem will disappear. This label is not used anywhere, but the behavior of gdb looks very strange. I tried to find a solution for a long time, but I am doing significant results. Using the gcc option "-fomit-frame-pointer" did not help. What can I do about it?

Gdb and gcc versions:

 arm-none-eabi-gdb --version GNU gdb (GDB) 7.1 .......... This GDB was configured as "--host=i686-pc-mingw32 --target=arm-none-eabi". arm-none-eabi-gcc --version arm-none-eabi-gcc (GCC) 4.5.1 

My MakeFile:

 TRGT = arm-none-eabi- CC = $(TRGT)gcc CP = $(TRGT)objcopy AS = $(TRGT)gcc -x assembler-with-cpp #AS = $(TRGT)as LD = $(TRGT)ld OBJDUMP = $(TRGT)objdump LD_SCRIPT = main.ld MCU = arm7tdmi #DEBUG = stabs DEBUG = dwarf-2 ASFLAGS = -mcpu=$(MCU) -g$(DEBUG) LDFLAGS = -T $(LD_SCRIPT) all: main.elf main.lss @echo Done! main.elf : main.o @echo Linking $< $(CC) -nostartfiles $(LDFLAGS) $< -o $@ main.o : main.s @echo Compiling $< $(AS) -c $(ASFLAGS) $< -o $@ 

Thanks in advance for your help!

Answer 1

try using "si" instead of n in the piece of code.

"n" is the more or less next instruction, "si" is the next asm instruction.

if the debug code for the asm part is incorrect, "si" can still allow you to execute it, taking advantage of the fact that in this case the level of "operator" and "assembler" is the same.

Answer 2

Use ni instead of next and si instead of step through assembly instructions.

Answer 3

I know this is a bit outdated, but you should try adding the -O0 flag to the compiler. I prevent gcc from doing any kind of optimization, which can lead to problems like the ones you have.