Re: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h

2009-09-14 Thread David Daney 

Geert Uytterhoeven wrote:

On Fri, Sep 11, 2009 at 17:58, David Daneydda...@caviumnetworks.com wrote:

Michael Buesch wrote:

On Friday 11 September 2009 01:56:42 David Daney wrote:

+/* Unreachable code */
+#ifndef unreachable
+# define unreachable() do { for (;;) ; } while (0)
+#endif

# define unreachable() do { } while (1)

? :)

Clearly I was not thinking clearly when I wrote that part.  RTH noted the
same thing.  I will fix it.


However, people are so used to seeing the `do { } while (0)' idiom,
that they might miss
there's a `1' here, not a `0'.

So perhaps it's better to use plain `for (;;)' for infinite loops?



I don't think so.  The only valid token that can follow 'do { } while 
(1)' is ';', any statement may follow 'for (;;)', so there is a greater 
possibility to silently screw things up with the for(;;) form.


David Daney

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Re: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h

2009-09-12 Thread Geert Uytterhoeven 
On Fri, Sep 11, 2009 at 17:58, David Daneydda...@caviumnetworks.com wrote:
 Michael Buesch wrote:

 On Friday 11 September 2009 01:56:42 David Daney wrote:

 +/* Unreachable code */
 +#ifndef unreachable
 +# define unreachable() do { for (;;) ; } while (0)
 +#endif

 # define unreachable() do { } while (1)

 ? :)

 Clearly I was not thinking clearly when I wrote that part.  RTH noted the
 same thing.  I will fix it.

However, people are so used to seeing the `do { } while (0)' idiom,
that they might miss
there's a `1' here, not a `0'.

So perhaps it's better to use plain `for (;;)' for infinite loops?

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say programmer or something like that.
-- Linus Torvalds
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Re: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h

2009-09-11 Thread Michael Buesch 
On Friday 11 September 2009 01:56:42 David Daney wrote:
 +/* Unreachable code */
 +#ifndef unreachable
 +# define unreachable() do { for (;;) ; } while (0)
 +#endif

# define unreachable() do { } while (1)

? :)

-- 
Greetings, Michael.
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Re: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h

2009-09-11 Thread David Daney 

Michael Buesch wrote:

On Friday 11 September 2009 01:56:42 David Daney wrote:

+/* Unreachable code */
+#ifndef unreachable
+# define unreachable() do { for (;;) ; } while (0)
+#endif


# define unreachable() do { } while (1)

? :)


Clearly I was not thinking clearly when I wrote that part.  RTH noted 
the same thing.  I will fix it.


Thanks,
David Daney
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[PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h

2009-09-10 Thread David Daney 
Starting with version 4.5, GCC has a new built-in function
__builtin_unreachable() that can be used in places like the kernel's
BUG() where inline assembly is used to transfer control flow.  This
eliminated the need for an endless loop in these places.

The patch adds a new macro 'unreachable()' that will expand to either
__builtin_unreachable() or an endless loop depending on the compiler
version.

Signed-off-by: David Daney dda...@caviumnetworks.com
CC: Thomas Gleixner t...@linutronix.de
CC: Ingo Molnar mi...@redhat.com
CC: H. Peter Anvin h...@zytor.com
CC: x...@kernel.org
CC: r...@linux-mips.org
CC: linux-m...@linux-mips.org
CC: Martin Schwidefsky schwidef...@de.ibm.com
CC: Heiko Carstens heiko.carst...@de.ibm.com
CC: linux...@de.ibm.com
CC: linux-s...@vger.kernel.org
CC: David Howells dhowe...@redhat.com
CC: Koichi Yasutake yasutake.koi...@jp.panasonic.com
CC: linux-am33-l...@redhat.com
CC: Kyle McMartin k...@mcmartin.ca
CC: Helge Deller del...@gmx.de
CC: linux-par...@vger.kernel.org
CC: Benjamin Herrenschmidt b...@kernel.crashing.org
CC: Paul Mackerras pau...@samba.org
CC: linuxppc-...@ozlabs.org
CC: Richard Henderson r...@twiddle.net
CC: Ivan Kokshaysky i...@jurassic.park.msu.ru
CC: linux-al...@vger.kernel.org
CC: Haavard Skinnemoen hskinnem...@atmel.com
CC: Mike Frysinger vap...@gentoo.org
CC: uclinux-dist-de...@blackfin.uclinux.org
---
 include/linux/compiler-gcc4.h |   14 ++
 include/linux/compiler.h  |5 +
 2 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index 450fa59..ab3af40 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -36,4 +36,18 @@
the kernel context */
 #define __cold __attribute__((__cold__))
 
+
+#if __GNUC_MINOR__ = 5
+/*
+ * Mark a position in code as unreachable.  This can be used to
+ * suppress control flow warnings after asm blocks that transfer
+ * control elsewhere.
+ *
+ * Early snapshots of gcc 4.5 don't support this and we can't detect
+ * this in the preprocessor, but we can live with this because they're
+ * unreleased.  Really, we need to have autoconf for the kernel.
+ */
+#define unreachable() __builtin_unreachable()
+#endif
+
 #endif
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 04fb513..7efd73f 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -144,6 +144,11 @@ void ftrace_likely_update(struct ftrace_branch_data *f, 
int val, int expect);
 # define barrier() __memory_barrier()
 #endif
 
+/* Unreachable code */
+#ifndef unreachable
+# define unreachable() do { for (;;) ; } while (0)
+#endif
+
 #ifndef RELOC_HIDE
 # define RELOC_HIDE(ptr, off)  \
   ({ unsigned long __ptr;  \
-- 
1.6.2.5

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Re: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h

2009-09-10 Thread Richard Henderson 

On 09/10/2009 04:56 PM, David Daney wrote:

+#ifndef unreachable
+# define unreachable() do { for (;;) ; } while (0)
+#endif


#define unreachable() do { } while (1)


r~
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