[Bug libc/34530] New: Regression in POWER fortified longjmp with pointer guard rotation

https://sourceware.org/bugzilla/show_bug.cgi?id=34530

            Bug ID: 34530
           Summary: Regression in POWER fortified longjmp with pointer
                    guard rotation
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---
            Target: powerpc*-linux-gnu

After commit 78f1f0e39cd41d28ae771eb3498bc33780c85cfd ("Consolidate the C
pointer guard and align the assembly implementations"), PTR_DEMANGLE3 on POWER
no longer atomically updates the destination register. The fortified longjmp
relies on atomic update of the stack pointer
sysdeps/powerpc/powerpc64/__longjmp-common.S:

#ifdef PTR_DEMANGLE
# ifdef CHECK_SP
        PTR_DEMANGLE3 (r22, r22, r25)
# else
        PTR_DEMANGLE3 (r1, r22, r25)
# endif
#endif

If a signal arrives at the wrong time, the kernel will see a garbage stack
pointer and fails to push the signal frame.

Seen as a nptl/tst-cancel32 failure.

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