On Fri, 17 Mar 2023, Jakub Jelinek wrote:
> On Fri, Mar 17, 2023 at 01:18:32PM +0100, Richard Biener wrote:
> > The following adds a missing range-op for __builtin_expect which
> > helps -Wuse-after-free to detect the case a realloc original
> > pointer is used when the result was NULL.
> >
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu, OK?
> >
> > PR tree-optimization/109170
> > * gimple-range-op.cc (cfn_expect): New.
> > (gimple_range_op_handler::maybe_builtin_call): Handle
> > __builtin_expect.
> >
> > * gcc.dg/Wuse-after-free-pr109170.c: New testcase.
>
> Shouldn't that be something we handle generically for all
> ERF_RETURNS_ARG calls (and not just for irange, but for any
> supported ranges)?
>
> Though, admittedly __builtin_expect probably doesn't set that
> and all the other current builtins with ERF_RETURNS_ARG return
> pointers I think.
Looking at builtin_fnspec we're indeed missing BUILT_IN_EXPECT,
but we could indeed use gimple_call_fnspec and look for a
returned argument. If it's not the first handling this
generically is going to be interesting wrt op?_range though,
so we'd need a range operator for each case (returns arg 1,
returns arg 2, more args are not supported?). Currently
all returns-arg builtins return the first arg, but eventually
modref or the fortran frontend will end up with calls returning
sth else.
If a float arg is returned it also needs to be a frange operator,
right?
Richard.
> So, I think LGTM, but give Andrew/Aldy a chance to chime in.
>
> > diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc
> > index a5d625387e7..f3d6e29e58d 100644
> > --- a/gcc/gimple-range-op.cc
> > +++ b/gcc/gimple-range-op.cc
> > @@ -309,6 +309,25 @@ public:
> > }
> > } op_cfn_constant_p;
> >
> > +// Implement range operator for integral CFN_BUILT_IN_EXPECT.
> > +class cfn_expect : public range_operator
> > +{
> > +public:
> > + using range_operator::fold_range;
> > + virtual bool fold_range (irange &r, tree, const irange &lh,
> > + const irange &, relation_trio) const
> > + {
> > + r = lh;
> > + return true;
> > + }
> > + virtual bool op1_range (irange &r, tree, const irange &lhs,
> > + const irange &, relation_trio) const
> > + {
> > + r = lhs;
> > + return true;
> > + }
> > +} op_cfn_expect;
> > +
> > // Implement range operator for CFN_BUILT_IN_SIGNBIT.
> > class cfn_signbit : public range_operator_float
> > {
> > @@ -966,6 +985,12 @@ gimple_range_op_handler::maybe_builtin_call ()
> > m_int = &op_cfn_parity;
> > break;
> >
> > + case CFN_BUILT_IN_EXPECT:
> > + m_valid = true;
> > + m_op1 = gimple_call_arg (call, 0);
> > + m_int = &op_cfn_expect;
> > + break;
> > +
> > default:
> > break;
> > }
> > diff --git a/gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c
> > b/gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c
> > new file mode 100644
> > index 00000000000..fa7dc66d66c
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c
> > @@ -0,0 +1,15 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -Wuse-after-free" } */
> > +
> > +unsigned long bufmax = 0;
> > +unsigned long __open_catalog_bufmax;
> > +void *realloc(void *, __SIZE_TYPE__);
> > +void free(void *);
> > +
> > +void __open_catalog(char *buf)
> > +{
> > + char *old_buf = buf;
> > + buf = realloc (buf, bufmax);
> > + if (__builtin_expect ((buf == ((void *)0)), 0))
> > + free (old_buf); /* { dg-bogus "used after" } */
> > +}
> > --
> > 2.35.3
>
> Jakub
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
