[Bug target/84574] New: Function return thunks shouldn't be aliased to indirect branch thunks

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84574

            Bug ID: 84574
           Summary: Function return thunks shouldn't be aliased to
                    indirect branch thunks
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
            Target: x86-64

Function return thunks shouldn't be aliased to indirect branch thunks
since indirect branch thunks are placed in COMDAT section and a COMDAT
section with indirect branch may not have return thunk:

[hjl@gnu-skx-1 xxx]$ cat x.i
void
foo (void)
{
}
[hjl@gnu-skx-1 xxx]$ cat y.i
extern void foo (void);

int
main ()
{
  foo ();
  return 0;
}
[hjl@gnu-skx-1 xxx]$ cat thunk.S
        .section       
.text.__x86_indirect_thunk,"axG",@progbits,__x86_indirect_thunk,comdat
        .globl  __x86_indirect_thunk
        .hidden __x86_indirect_thunk
        .type   __x86_indirect_thunk, @function
__x86_indirect_thunk:
.LFB1:
        .cfi_startproc
        call    .LIND3
.LIND2:
        lfence
        jmp     .LIND2
.LIND3:
        lea     8(%rsp), %rsp
        ret
        .cfi_endproc
.LFE1:
        .section        .note.GNU-stack,"",@progbits
[hjl@gnu-skx-1 xxx]$ make
/export/build/gnu/gcc-test/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-test/build-x86_64-linux/gcc/    -c -o thunk.o thunk.S
/export/build/gnu/gcc-test/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-test/build-x86_64-linux/gcc/ -O2
-mindirect-branch=thunk -c y.i
/export/build/gnu/gcc-test/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-test/build-x86_64-linux/gcc/ -O2
-mindirect-branch=thunk -mfunction-return=thunk -c x.i
/export/build/gnu/gcc-test/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-test/build-x86_64-linux/gcc/ -O2
-mindirect-branch=thunk -o x thunk.o y.o x.o
/usr/local/bin/ld: x.o: in function `foo':
x.i:(.text+0x1): undefined reference to `__x86_return_thunk'
collect2: error: ld returned 1 exit status
make: *** [Makefile:30: x] Error 1
[hjl@gnu-skx-1 xxx]$