Purpose of PTRACE_SETSIGINFO for x86

Okash Khawaja okash.khawaja at gmail.com
Fri Dec 14 17:30:42 EST 2018


What does the PTRACE_SETSIGINFO ptrace command do?

I can see in kernel/ptrace.c:ptrace_request() it calls
ptrace_setsiginfo(), passing it the child's (tracee's) task descriptor
and siginfo_t instance originally passed in from user space.

ptrace_setsiginfo() sets child's last_siginfo to the siginfo_t
instance passed in. Now there are only two places where a
child->last_siginfo's value is read are in kernel/ptrace.c:

1. by the ptrace command PTRACE_GETSIGINFO
2. by the ptrace command PTRACE_LISTEN

There doesn't seem to be a place where value of last_siginfo is read
by signal handling code. There is however this comment in

 * Update the siginfo structure if the signal has
 * changed.  If the debugger wanted something
 * specific in the siginfo structure then it should
 * have updated *info via PTRACE_SETSIGINFO.

Where does PTRACE_SETSIGINFO update *info?


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