CODEWITHSUNDEEP
debuggingassemblygdbarm
engie
engie

Reputation: 2819

How do I set a software breakpoint on an ARM processor?

How do I do the equivalent of an x86 software interrupt:

asm( "int $3" )

on an ARM processor (specifically a Cortex A8) to generate an event that will break execution under gdb?

Upvotes: 29

Views: 48919

Answers (8)

J1ngB0
J1ngB0

Reputation: 51

We can use breakpoint inst:

Or we can use UND pseudo-instruction to generate undefined instruction which will cause exception if processor attempt to execute it.

Upvotes: 3

Olsonist
Olsonist

Reputation: 2393

Although the original question asked about Cortex-A7 which is ARMv7-A, on ARMv8 GDB uses

brk #0

Upvotes: 3

Philippe De Muyter
Philippe De Muyter

Reputation: 281

On my armv7hl (i.MX6q with linux 4.1.15) system, to set a breakpoint in another process, I use :

ptrace(PTRACE_POKETEXT, pid, address, 0xe7f001f0)

I choose that value after strace'ing gdb :)

This works perfectly : I can examine the traced process, restore the original instruction, and restart the process with PTRACE_CONT.

Upvotes: 3

Benny
Benny

Reputation: 4321

__asm__ __volatile__ ("bkpt #0");

See BKPT man entry.

Upvotes: 9

scottt
scottt

Reputation: 7228

I have a simple library (scottt/debugbreak) just for this:

#include <debugbreak.h>
...
debug_break();

Just copy the single debugbreak.h header into your code and it'll correctly handle ARM, AArch64, i386, x86-64 and even MSVC.

Upvotes: 9

Thomson
Thomson

Reputation: 21615

For Windows on ARM, the instrinsic __debugbreak() still works which utilizes undefined opcode.

nt!DbgBreakPointWithStatus:
defe     __debugbreak

Upvotes: 3

benathon
benathon

Reputation: 7635

Using arm-none-eabi-gdb.exe cross compiler, this works great for me (thanks to Igor's answer):

__asm__("BKPT");

Upvotes: 30

Igor Skochinsky
Igor Skochinsky

Reputation: 25268

ARM does not define a specific breakpoint instruction. It can be different in different OSes. On ARM Linux it's usually an UND opcode (e.g. FE DE FF E7) in ARM mode and BKPT (BE BE) in Thumb.

With GCC compilers, you can usually use __builtin_trap() intrinsic to generate a platform-specific breakpoint. Another option is raise(SIGTRAP).

Upvotes: 22

Related Questions