On Mon, 22 Sep 2014 19:15:25 +0200 Oleg Nesterov <o...@redhat.com> wrote:
> format_corename() can only pass the leader's pid to the core handler, but > there is no simple way to figure out which thread originated the coredump. > > As Jan explains, this also means that there is no simple way to create the > backtrace of the crashed process: > > As programs are mostly compiled with implicit gcc -fomit-frame-pointer one > needs program's .eh_frame section (equivalently PT_GNU_EH_FRAME segment) or > .debug_frame section. .debug_frame usually is present only in separate debug > info files usually not even installed on the system. While .eh_frame is a > part of the executable/library (and it is even always mapped for C++ > exceptions unwinding) it no longer has to be present anywhere on the disk > as the program could be upgraded in the meantime and the running instance > has its executable file already unlinked from disk. > > One possibility is to echo 0x3f >/proc/*/coredump_filter and dump all the > file-backed memory including the executable's .eh_frame section. But that > can create huge core files, for example even due to mmapped data files. > > Other possibility would be to read .eh_frame from /proc/PID/mem at the > core_pattern handler time of the core dump. For the backtrace one needs to > read the register state first which can be done from core_pattern handler: > > ptrace(PTRACE_SEIZE, tid, 0, PTRACE_O_TRACEEXIT) > close(0); // close pipe fd to resume the sleeping dumper > waitpid(); // should report EXIT > PTRACE_GETREGS or other requests > > The remaining problem is how to get the 'tid' value of the crashed thread. > It could be read from the first NT_PRSTATUS note of the core file but that > makes the core_pattern handler complicated. > > Unfortunately %t is already used so this patch uses %i/%I. Is any userspace actually going to use this? If so, details? Am wondering what is driving this change... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
