https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79352
Bug ID: 79352
Summary: [6 Regression] -fprintf-return-value doesn't handle
flexible-like array members properly
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
Most of the optimization passes handle flexible array members and trailing
arrays in structures that could be poor man's flexible array members
conservatively, but apparently gimple-ssa-sprintf.c does not.
char buf[64];
struct S { int i; char j[1]; };
__attribute__((noinline, noclone)) void
foo (struct S *p)
{
int a = __builtin_sprintf (buf, "a%sf", p->j);
if (a != 6)
__builtin_abort ();
}
int
main ()
{
struct S *s = __builtin_malloc (sizeof (struct S) + 4);
if (s)
{
s->i = 5;
__builtin_strcpy (s->j, "bcde");
foo (s);
__builtin_free (s);
}
return 0;
}
ICEs because of that, the pass thinks that p->j must be "", while in foo it can
be arbitrary length. If you try to print __builtin_object_size (s->j, {0,1})
before the call to foo, it prints 8 (that is sizeof (struct S) + 4 - offsetof
(struct S, s->j[0])), if you try to print __builtin_object_size (p->j, {0,1})
inside of foo, it will correctly print -1, don't know length.
