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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/102027] New: ABI break when using vector type in
 function arg/return value
Date: Mon, 23 Aug 2021 18:10:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102027

            Bug ID: 102027
           Summary: ABI break when using vector type in function
                    arg/return value
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

We have an ABI break.  Discovered by
Running
/root/rpmbuild/BUILD/gcc-11.2.1-20210728/gcc/testsuite/gcc.dg/compat/struct=
-layout-1.exp
...
FAIL: tmpdir-gcc.dg-struct-layout-1/t025 c_compat_x_tst.o-c_compat_y_alt.o
execute=20
FAIL: tmpdir-gcc.dg-struct-layout-1/t025 c_compat_x_alt.o-c_compat_y_tst.o
execute

Started with r11-263.

$ cat m.c
extern void test2237();
int main() { test2237(); }
$ cat x.c
#include "x.h"
extern struct U2SF check2237();
void test2237() { check2237(); }
$ cat y.c
#include "x.h"
struct U2SF check2237_ret;

struct U2SF check2237() {
  return check2237_ret;
}
$ cat x.h
struct U2SF {
  __attribute__((__vector_size__(2 * sizeof(float)))) float v;
};

$ xgcc-11 -c m.c
$ xgcc-11 -c x.c
$ xgcc-10 -c y.c
$ xgcc-11 m.o x.o y.o -o foo
./foo
Segmentation fault      (core dumped)

while
$ xgcc-11 -c y.c
$ xgcc-11 m.o x.o y.o -o foo
$ ./foo
# OK

$ gdb ./foo
(gdb) r
Starting program: /home/mpolacek/x/trunk/gcc/foo=20

Program received signal SIGSEGV, Segmentation fault.
0x000000000040113f in check2237 ()
(gdb) bt
#0  0x000000000040113f in check2237 ()
#1  0x0000000000401129 in test2237 ()
#2  0x0000000000401114 in main ()
(gdb) disas
Dump of assembler code for function check2237:
   0x000000000040112c <+0>:     push   %rbp
   0x000000000040112d <+1>:     mov    %rsp,%rbp
   0x0000000000401130 <+4>:     mov    %rdi,-0x8(%rbp)
   0x0000000000401134 <+8>:     mov    -0x8(%rbp),%rax
   0x0000000000401138 <+12>:    mov    0x2ef1(%rip),%rdx        # 0x404030
<check2237_ret>
=3D> 0x000000000040113f <+19>:    mov    %rdx,(%rax)
   0x0000000000401142 <+22>:    mov    -0x8(%rbp),%rax
   0x0000000000401146 <+26>:    pop    %rbp
   0x0000000000401147 <+27>:    ret=20=20=20=20
End of assembler dump.=