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[Bug 162774] strace ignores int3 SIGTRAP



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https://bugzilla.redhat.com/show_bug.cgi?id=162774





--- Comment #8 from Denys Vlasenko <dvlasenk redhat com>  2008-09-10 11:44:57 EDT ---
The "bug" of extra SIGTRAP which patch works around is not really a bug, it's a
feature of execve:

NAME
       execve - execute program
DESCRIPTION
...
       If  the current program is being ptraced, a SIGTRAP is sent to it after
       a successful execve().
...

This extra SIGTRAP is not affected by PTRACE_O_TRACESYSGOOD option. In my
opinion, this SIGTRAP should not be passed to straced program as this may
change its behavior, so handling of this SIGTRAP as coded in the patch is
correct, only comment

+  /* Kernel bug (observed on 2.6.25 x86_64):
+   * even if we set PTRACE_O_TRACESYSGOOD option,
+   * after execve(), post-syscall ptrace-generated SIGTRAP
+   * has signo == SIGTRAP, not (SIGTRAP | 0x80)!
+   * Detect it by looking at siginfo.
+   */

nees changing. I am not sure whether the detection is future-proof (why kernel
doesn't fill in correct si.si_signo? What would happen if it would be fixed in
kernel? etc), but so far it works.

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