CODEWITHSUNDEEP
macosassemblynasmx86-64lldb
zMesh
zMesh

Reputation: 78

Assembly - Unable to set breakpoints lldb

I assembled with these options nasm -O0 -g -f macho64 but lldb complains of "Unable to resolve breakpoint to any actual locations." when i try to set any breakpoints at line numbers in the file.

I've started trying to learn 64 bit assembly for OS X but it's proving a real challenge so far, there seems to be hardly any resources for learning.

Upvotes: 4

Views: 2439

Answers (1)

Jason Molenda
Jason Molenda

Reputation: 15375

Your assembler probably didn't emit any debug information for the binary you created. You can tell by running dwarfdump --debug-line on your .o file or on the .dSYM bundle for your binary if there is one.

Load the binary into lldb and run the disassemble -n function-name command. That will show you the assembly - then you can set a breakpoint with breakpoint set -a address. By default lldb will run your binary with address space randomization (ASLR) turned off -- so the binary will run at the same address every time, instead of loading your program at a randomized address.

A simple example:

%  echo 'int main () { }' > a.c
% clang a.c
% lldb a.out
(lldb) target create "a.out"
Current executable set to 'a.out' (x86_64).
(lldb) disass -n main
a.out`main:
a.out[0x100000fb0] <+0>: pushq  %rbp
a.out[0x100000fb1] <+1>: movq   %rsp, %rbp
a.out[0x100000fb4] <+4>: xorl   %eax, %eax
a.out[0x100000fb6] <+6>: popq   %rbp
a.out[0x100000fb7] <+7>: retq   

(lldb) br s -a 0x100000fb4
Breakpoint 1: address = 0x0000000100000fb4
(lldb) r
Process 32406 launched: '/private/tmp/a.out' (x86_64)
Process 32406 stopped
* thread #1: tid = 0x145576, 0x0000000100000fb4 a.out`main + 4, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100000fb4 a.out`main + 4
a.out`main:
->  0x100000fb4 <+4>: xorl   %eax, %eax
    0x100000fb6 <+6>: popq   %rbp
    0x100000fb7 <+7>: retq   
    0x100000fb8:      addl   %eax, (%rax)
(lldb)

Upvotes: 6

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