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Re: [PATCH] i386: Define __HAVE_INDIRECT_RETURN_ATTRIBUTE__


On Thu, Jul 19, 2018 at 01:39:04PM +0200, Florian Weimer wrote:
> On 07/19/2018 01:33 PM, Jakub Jelinek wrote:
> > On Thu, Jul 19, 2018 at 04:21:26AM -0700, H.J. Lu wrote:
> > > The new indirect_return attribute is intended to mark swapcontext in
> > > <ucontext.h>.  This patch defines __HAVE_INDIRECT_RETURN_ATTRIBUTE__
> > > so that it can be used checked before using indirect_return attribute
> > > in <ucontext.h>.  It works when the indirect_return attribute is
> > > backported to GCC 8.
> > > 
> > > OK for trunk?
> > 
> > No.  Use
> > #ifdef __has_attribute
> > #if __has_attribute (indirect_return)
> > ...
> > #endif
> > #endif
> > instead, like for any other attribute.
> 
> That doesn't work because indirect_return is not in the implementation
> namespace and expanded in this context. I assume that __has_attribute
> (__indirect_return__) would work, though.
> 
> Could we add:
> 
> #ifdef __has_attribute
> # define __glibc_has_attribute(attr) __has_attribute (attr)
> #else
> # define __glibc_has_attribute 0
> #endif
> 
> And then use this:
> 
> #if __glibc_has_attribute (__indirect_return__)
> 
> Would that still work?
> 

Both __has_attribute (indirect_return) and __has_attribute (__indirect_return__)
work here.


H.J.
---
The new indirect_return attribute is intended to mark swapcontext in
<ucontext.h>.  Test __has_attribute (indirect_return) so that it
can be backported to GCC 8.

	PR target/86560
	* gcc.target/i386/pr86560-4.c: New test.
	* gcc.target/i386/pr86560-5.c: Likewise.
---
 gcc/testsuite/gcc.target/i386/pr86560-4.c | 21 +++++++++++++++++++++
 gcc/testsuite/gcc.target/i386/pr86560-5.c | 21 +++++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr86560-4.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr86560-5.c

diff --git a/gcc/testsuite/gcc.target/i386/pr86560-4.c b/gcc/testsuite/gcc.target/i386/pr86560-4.c
new file mode 100644
index 00000000000..a623e3dcbeb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr86560-4.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection" } */
+/* { dg-final { scan-assembler-times {\mendbr} 2 } } */
+
+struct ucontext;
+
+extern int (*bar) (struct ucontext *)
+#ifdef __has_attribute
+# if __has_attribute (indirect_return)
+  __attribute__((__indirect_return__))
+# endif
+#endif
+;
+
+extern int res;
+
+void
+foo (struct ucontext *oucp)
+{
+  res = bar (oucp);
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr86560-5.c b/gcc/testsuite/gcc.target/i386/pr86560-5.c
new file mode 100644
index 00000000000..33b0f6424c2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr86560-5.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection" } */
+/* { dg-final { scan-assembler-times {\mendbr} 2 } } */
+
+struct ucontext;
+
+extern int (*bar) (struct ucontext *)
+#ifdef __has_attribute
+# if __has_attribute (__indirect_return__)
+  __attribute__((__indirect_return__))
+# endif
+#endif
+;
+
+extern int res;
+
+void
+foo (struct ucontext *oucp)
+{
+  res = bar (oucp);
+}
-- 
2.17.1


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