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From: "palmer at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/114175] [13/14] RISC-V: Execution test failures on
 gcc.dg/c23-stdarg-6.c
Date: Thu, 29 Feb 2024 21:28:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114175

palmer at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-02-29
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #14 from palmer at gcc dot gnu.org ---
Looks like it's a problem with the struct return argument mixing with va_st=
art
/ va_arg.  This much smaller test case still fails, and on gcc-13

$ cat gcc/testsuite/gcc.dg/c23-stdarg-6.c
/* Test C23 variadic functions with no named parameters, or last named
   parameter with a declaration not allowed in C17.  Execution tests.  */
/* { dg-do run } */
/* { dg-options "-std=3Dc23 -pedantic-errors" } */

#include <stdarg.h>
#include <stdio.h>

extern void abort (void);
extern void exit (int);
struct s { char c[1000]; };

struct s
f (...)
{
  va_list ap;
  va_start (ap);
  double r =3D va_arg (ap, int);
  va_end (ap);
  struct s ret =3D {};
  ret.c[0] =3D r;
  ret.c[999] =3D 42;
  return ret;
}

int
main ()
{
  struct s x =3D f (1);
  fprintf(stderr, "%d\n", x.c[0]);
  if (x.c[0] !=3D 1)
    abort ();
  exit (0);
}
$ riscv64-unknown-linux-gnu-gcc gcc/testsuite/gcc.dg/c23-stdarg-6.c -o test
-std=3Dc2x -static -O3
$ qemu-riscv64 ./test
16
Aborted

The output value seems to change from time to time, which smells like some
uninitialized access.  I'd bet we're just not properly skipping over the ou=
tput
stack space in riscv_va_start().  Not quite sure where to start, though, as
ours is so much simpler than arm64 that it's going to take a bit to figure =
out
what's going on.=