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From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/15868] New: backtrace interfaces and calls to noreturn functions
Date: Tue, 20 Aug 2013 20:13:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=15868

            Bug ID: 15868
           Summary: backtrace interfaces and calls to noreturn functions
           Product: glibc
           Version: 2.18
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org
                CC: drepper.fsp at gmail dot com

Created attachment 7155
  --> http://sourceware.org/bugzilla/attachment.cgi?id=7155&action=edit
Testcase

The backtrace / backtrace_symbols / backtrace_symbols_fd interfaces do not work
well when backtracing through calls to noreturn functions (a natural use case -
a noreturn error-handling function might reasonably wish to print a backtrace).

This is illustrated by the attached testcase on x86_64.  At least with some GCC
versions, the call to a noreturn function has return address pointing to
padding after the end of the calling function, meaning that it does not point
inside that function and so a name for it cannot be found.

The backtrace interface is that the addresses are return addresses.  But
reliable backtracing requires additional information about whether frames are
signal frame, in which case the return address points inside the relevant
function, or not, in which case you should subtract 1 to be sure of being
inside the relevant function.  (That involves calling _Unwind_GetIPInfo instead
of _Unwind_GetIP to get the relevant information.)  So to support this case
reliably, there should be new interfaces that handle this adjustment in some
way.

(Old discussion started at:
http://www.eglibc.org/archives/patches/msg01077.html .)

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