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From: "linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/99888] Add powerpc ELFv2 support for
 -fpatchable-function-entry*
Date: Wed, 03 Aug 2022 02:53:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99888

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
                 CC|                            |linkw at gcc dot gnu.org
   Last reconfirmed|                            |2022-08-03
           Assignee|unassigned at gcc dot gnu.org      |linkw at gcc dot gn=
u.org

--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
cat test.c=20

extern int a;
int foo (int b){
  return a + b;
}

on ppc64le, with option "-mcpu=3Dpower9 -fpatchable-function-entry=3D5,3", =
the
generated assembly looks like:

.LPFE1:
        nop
        nop
        nop
        .type   foo, @function
foo:
        nop
        nop
.LFB0:
        .cfi_startproc
.LCF0:
0:      addis 2,12,.TOC.-.LCF0@ha
        addi 2,2,.TOC.-.LCF0@l
        .localentry     foo,.-foo
        std 31,-8(1)

Jakub's #c0 noted that the "after" nops should be placed after local entry,=
 but
there seem two choices to put the "before" nops, such as:

1)

0:      addis 2,12,.TOC.-.LCF0@ha
        addi 2,2,.TOC.-.LCF0@l
        nop
        nop
        nop
        .localentry     foo,.-foo
        nop
        nop
        std 31,-8(1)

2)

0:      nop
        nop
        nop
        addis 2,12,.TOC.-.LCF0@ha
        addi 2,2,.TOC.-.LCF0@l
        .localentry     foo,.-foo
        nop
        nop
        std 31,-8(1)

For either of them, the "before" nops only take effects when it's entered f=
rom
global entry, both are counted as five insns in global entry area, there is=
 no
differences from these two perspectives. I'd like to go with 1) if no
objections.=