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[Bug libc/13092] New: Profiling on powerpc32 secure-plt shared libs and PIEs segfaults
- From: "amodra at gmail dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Mon, 15 Aug 2011 02:40:58 +0000
- Subject: [Bug libc/13092] New: Profiling on powerpc32 secure-plt shared libs and PIEs segfaults
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=13092
Bug #: 13092
Summary: Profiling on powerpc32 secure-plt shared libs and PIEs
segfaults
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: libc
AssignedTo: drepper.fsp@gmail.com
ReportedBy: amodra@gmail.com
Classification: Unclassified
Profiling of shared libraries and PIEs has been broken ever since the
introduction of secure-plt for powerpc32. The problem is that a ppc32 PIC PLT
call stub uses r30 (GOT pointer) to load the function address from the PLT, r30
being set up in the function prologue, but _mcount is called before the
function prologue. So chances are good that r30 will be pointing to the
executable GOT when trying to call _mcount in a shared lib function. A similar
problem can occur in a PIE if a shared lib calls a function in the executable.
Thus it is not possible to call _mcount via a PIC PLT call stub. Changing the
stub just for _mcount would be possible, but would require followup changes to
exception handling and gdb. Changing gcc code would either result in bloat to
-pg objects or ABI changes for _mcount, breaking user _mcount implementations.
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