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From: "tuliom at ascii dot art.br" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/101324] New: powerpc64le: hashst appears before mflr at
 -O1 or higher
Date: Mon, 05 Jul 2021 15:32:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101324

            Bug ID: 101324
           Summary: powerpc64le: hashst appears before mflr at -O1 or
                    higher
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tuliom at ascii dot art.br
  Target Milestone: ---

Created attachment 51105
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51105&action=3Dedit
__memmove_ppc extracted from glibc

When using ROP (-mrop-protect), it's expected that generated code reads the
value from LR (mflr) and hash it later (hashst).

This works well at -O0.
However, at -O1 and higher, we're seeing cases where hashst appears before
mflr.

I'm attaching an example extracted from glibc.

You can reproduce the issue with command:
gcc -S -O1 -mrop-protect -mcpu=3Dpower10 memmove-ppc64.i -o -


The generated asm contains the following:

__memmove_ppc:
.LFB6:
        .cfi_startproc
        .localentry     __memmove_ppc,1
        hashst 0,-40(1)
        std 28,-32(1)
        stdu 1,-80(1)
        .cfi_def_cfa_offset 80
        .cfi_offset 28, -32
        mr 28,3
        subf 9,4,3
        cmpld 0,9,5
        bge 0,.L17
        std 31,72(1)
        .cfi_offset 31, -8
        add 4,4,5
        add 31,3,5
        cmpldi 0,5,15
        ble 0,.L4
        mflr 0
...=