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?
(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();
+}
