On Thu, Jun 2, 2011 at 2:02 PM, Mikael Pettersson <mi...@it.uu.se> wrote:
> GCC has attribute((returns_twice)) which is supposed to allow the safe
> use of alternate implementations of setjmp-like functions. In particular,
> a function that calls a setjmp-like function must itself not be inlined,
> because that would enable unsafe optimizations. This works for calls to
> "setjmp" (a few alternate spellings are allowed), but not to e.g. "my_setjmp"
> even if that function is declared with attribute((returns_twice)). This
> bug affects the entire gcc-4.x series, gcc-3.x worked; see PR49243.
>
> A function that calls "setjmp" is marked non-inlinable because setjmp_call_p
> is applied to the function position, and it deduces via special_function_p
> that the callee is ECF_RETURNS_TWICE. But special_function_p only looks at
> the name, so setjmp_call_p fails to detect attribute((returns_twice)) callees.
>
> The fix is to have setjmp_call_p also check if the returns_twice attribute
> is present, via DECL_IS_RETURNS_TWICE. It could call flags_from_decl_or_type
> instead, but that would perform quite a bit of redundant work for this case.
>
> The test case uses -Winline to check that gcc refuses to inline a function
> that calls a returns_twice callee. This is sufficient to verify the fix, and
> avoids the machine-specific code needed in the original runtime test case.
>
> Tested w/o regressions with gcc trunk and 4.6 on x86_64-linux. The added test
> case does fail without the fix and pass with it.
>
> OK for trunk, and perhaps 4.6?
Ok. I'll take care of applying it.
Thanks,
Richard.
> (I don't have svn write access.)
>
> /Mikael
>
> gcc/
>
> 2011-06-02 Mikael Pettersson <mi...@it.uu.se>
>
> PR tree-optimization/49243
> * calls.c (setjmp_call_p): Also check if fndecl has the
> returns_twice attribute.
>
> gcc/testsuite/
>
> 2011-06-02 Mikael Pettersson <mi...@it.uu.se>
>
> PR tree-optimization/49243
> * gcc.dg/pr49243.c: New.
>
> --- gcc-4.7-20110528/gcc/calls.c.~1~ 2011-05-25 13:00:14.000000000 +0200
> +++ gcc-4.7-20110528/gcc/calls.c 2011-06-02 12:55:32.000000000 +0200
> @@ -554,6 +554,8 @@ special_function_p (const_tree fndecl, i
> int
> setjmp_call_p (const_tree fndecl)
> {
> + if (DECL_IS_RETURNS_TWICE (fndecl))
> + return ECF_RETURNS_TWICE;
> return special_function_p (fndecl, 0) & ECF_RETURNS_TWICE;
> }
>
> --- gcc-4.7-20110528/gcc/testsuite/gcc.dg/pr49243.c.~1~ 1970-01-01
> 01:00:00.000000000 +0100
> +++ gcc-4.7-20110528/gcc/testsuite/gcc.dg/pr49243.c 2011-06-02
> 12:55:32.000000000 +0200
> @@ -0,0 +1,25 @@
> +/* PR tree-optimization/49243 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Winline" } */
> +
> +extern unsigned long jb[];
> +extern int my_setjmp(unsigned long jb[]) __attribute__((returns_twice));
> +extern int decode(const char*);
> +
> +static inline int wrapper(const char **s_ptr) /* { dg-warning "(inlining
> failed|function 'wrapper' can never be inlined because it uses setjmp)" } */
> +{
> + if (my_setjmp(jb) == 0) {
> + const char *s = *s_ptr;
> + while (decode(s) != 0)
> + *s_ptr = ++s;
> + return 0;
> + } else
> + return -1;
> +}
> +
> +void parse(const char *data)
> +{
> + const char *s = data;
> + if (!(wrapper(&s) == -1 && (s - data) == 1)) /* { dg-warning "called
> from here" } */
> + __builtin_abort();
> +}
>
