[Bug c/38483] New: generated aborts lose previous side-effects

[jsm28 at gcc dot gnu dot org]

When the compiler generates an abort for runtime-undefined code, the abort
can be executed too soon when side-effects before the undefined behavior
might have caused the undefined behavior not to happen after all.

For calls to functions cast to incompatible types, the undefined behavior
happens when the call does, which is after all the arguments (and the function
designator) have been evaluated.  So they need to be evaluated for their
side-effects before the abort is evaluated.  The following testcase illustrates
this; it should exit successfully but instead aborts.

extern void exit (int);
extern void abort (void);

int
foo (void)
{
  exit (0);
  return 0;
}

void
bar (void)
{
}

int
main (void)
{
  ((long (*)(int))bar) (foo ());
  abort ();
}

Much the same applies to va_arg, although the validity of the programs in this
case is less clear (because the argument passed to va_arg isn't actually
an object declared by the calling function).

#include <stdarg.h>

extern void exit (int);
extern void abort (void);

va_list ap;
float f;

va_list *
foo (void)
{
  exit (0);
  return &ap;
}

void
bar (int i, ...)
{
  va_start (ap, i);
  f = va_arg (*foo (), float);
  va_end (ap);
}

int
main (void)
{
  bar (1, 0);
  abort ();
}


-- 
           Summary: generated aborts lose previous side-effects
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jsm28 at gcc dot gnu dot org
OtherBugsDependingO 16620,16989
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38483