which signal does gdb send when attaching to a process?

2
votes

Which signal does gdb send when attaching to a process? Does this work the same for different UNIXes. E.g. Linux and Mac OS X?

So far I only found out, that SIGTRAP is used to implement breakpoints. Is it used for attaching aswell?

1
unixgdbsignals

1 Answers

2
votes

AFAIK it does not need any signals to attach. It just suspends the "inferior" by calling ptrace. It also reads debugged process memory and registers using this calls and it can request instruction single stepping (provided it's implemented on that port of linux), etc. Software breakpoints are implemented by placing at right location instruction that triggers "trap" or something similar when reached, but debugged process can run full speed until then.

Also (next to reading man ptrace, as already mentioned) see ptrace explanation on wikipedia.