[Bug c/59039] Undocumented __builtin_longjmp/__builtin_setjmp

[sandra at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59039

sandra at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |sandra at gcc dot gnu.org

--- Comment #30 from sandra at gcc dot gnu.org ---
I've been looking at this issue.  The proposed patch has a number of problems,
notably that it uses "@code{setjmp} buffer" to describe the argument that is
*not* the same as the buffer you would pass to the setjmp function.  (It's a
different flavor of buffer.)

I'm also thinking that "@code{__builtin_setjmp} and @code{__builtin_longjmp}
may not be used in the same function with the same @code{setjmp} buffer"
doesn't accurately capture the restriction.  If builtin_setjmp uses its
containing function's prologue/epilogue to do the register saves and restores
(comment 25), it seems like that also implies that builtin_longjmp can only be
called from functions called directly or indirectly from that containing
function.  And indeed, at least on nios2-elf this program wanders off into the
weeds:

#include <stdint.h>

int
my_setjmp (intptr_t *buf)
{
  return __builtin_setjmp (buf);
}

void
my_longjmp (intptr_t *buf)
{
  __builtin_longjmp (buf, 1);
}

int
main (void)
{
  intptr_t buf[5];
  int ret;

  ret = my_setjmp (buf);
  if (ret == 0)
    my_longjmp (buf);
  return ret;
}

whereas calling __builtin_setjmp directly from main works and returns 1 as
expected.