[uml-devel] [PATCH] Fix for 2.6.26 ptrace crash

[uml-devel] [PATCH] Fix for 2.6.26 ptrace crash

[Jeff Dike]

I believe I figured out the ptrace crash that showed up with 2.6.26,
thanks to Toralf Förster.

The patch is below.

I have one confirmation that this fixes the problem - I'd like a few
more just to be sure.

			Jeff

-- 
Work email - jdike at linux dot intel dot com

Index: linux-2.6.22/arch/um/include/init.h
===================================================================
--- linux-2.6.22.orig/arch/um/include/init.h	2008-02-18 11:53:50.000000000 -0500
+++ linux-2.6.22/arch/um/include/init.h	2008-07-20 18:06:35.000000000 -0400
@@ -45,6 +45,8 @@ typedef void (*exitcall_t)(void);
 # define __section(S) __attribute__ ((__section__(#S)))
 #endif
 
+#if __GNUC__ == 3
+
 #if __GNUC_MINOR__ >= 3
 # define __used			__attribute__((__used__))
 #else
@@ -52,6 +54,12 @@ typedef void (*exitcall_t)(void);
 #endif
 
 #else
+#if __GNUC__ == 4
+# define __used			__attribute__((__used__))
+#endif
+#endif
+
+#else
 #include <linux/compiler.h>
 #endif
 /* These are for everybody (although not all archs will actually

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Re: [uml-devel] [uml-user] [PATCH] Fix for 2.6.26 ptrace crash

[vincent-perrier]

Hello,
I also had the crash with a lot of zeros in a vertical line with kernel
2.6.26, I was sad then.
But I am now happy, I applied the patch:

bash-3.1# cd linux-2.6.26
bash-3.1# patch -p1 < ../jeff.patch
patching file arch/um/include/init.h
Hunk #1 succeeded at 45 with fuzz 2.
Hunk #2 succeeded at 54 with fuzz 1.

And my 2.6.26 uml machine worked!!

All this to say: I confirm the patch worked for me too.

Regards


On Mon, 2008-07-21 at 11:46 -0400, Jeff Dike wrote:
> I believe I figured out the ptrace crash that showed up with 2.6.26,
> thanks to Toralf Förster.
> 
> The patch is below.
> 
> I have one confirmation that this fixes the problem - I'd like a few
> more just to be sure.
> 
> 			Jeff
> 


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Re: [uml-devel] [PATCH] Fix for 2.6.26 ptrace crash

[Peter Teoh]

Thanks, the patch worked for me too.

As an aside, may be u would want to sync with mainline:

http://lkml.org/lkml/2007/5/3/460

which would solve the problem Boaz posed as well?

(the patch above seemed to indicate a problem of post-3.4 vs pre-3.4 GCC:

http://www.gnu.org/software/gcc/gcc-3.4/changes.html

but your patch indicated something to do with 4.x GCC vs pre-3.4 GCC?)

Sorry if I don't get it correctly :-).

On Mon, Jul 21, 2008 at 11:46 PM, Jeff Dike <jdike@addtoit.com> wrote:
> I believe I figured out the ptrace crash that showed up with 2.6.26,
> thanks to Toralf Förster.
>
> The patch is below.
>
> I have one confirmation that this fixes the problem - I'd like a few
> more just to be sure.
>
>                        Jeff
>
> --
> Work email - jdike at linux dot intel dot com
>
> Index: linux-2.6.22/arch/um/include/init.h
> ===================================================================
> --- linux-2.6.22.orig/arch/um/include/init.h    2008-02-18 11:53:50.000000000 -0500
> +++ linux-2.6.22/arch/um/include/init.h 2008-07-20 18:06:35.000000000 -0400
> @@ -45,6 +45,8 @@ typedef void (*exitcall_t)(void);
>  # define __section(S) __attribute__ ((__section__(#S)))
>  #endif
>
> +#if __GNUC__ == 3
> +
>  #if __GNUC_MINOR__ >= 3
>  # define __used                        __attribute__((__used__))
>  #else
> @@ -52,6 +54,12 @@ typedef void (*exitcall_t)(void);
>  #endif
>
>  #else
> +#if __GNUC__ == 4
> +# define __used                        __attribute__((__used__))
> +#endif
> +#endif
> +
> +#else
>  #include <linux/compiler.h>
>  #endif
>  /* These are for everybody (although not all archs will actually
>



-- 
Regards,
Peter Teoh

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Re: [uml-devel] [PATCH] Fix for 2.6.26 ptrace crash

[Jeff Dike]

On Tue, Jul 22, 2008 at 11:27:13AM +0300, Boaz Harrosh wrote:
> I'm not sure I fully understand. Could you please explain what you
> found.

arch/um/include/init.h copies enough definitions from linux/compiler.h
and linux/init.h to implement initcall and exitcall et al.  It can't
include the kernel headers because it's included in userspace files,
and libc and kernel headers don't mix.

What happened was that I copied enough to make a distinction between
gcc 3.3 and higher vs lower than 3.3 (for the latter, the kernel
defines __used as attribute(__unused) for some reason).

However, since my ifdefs weren't looking at the major version, these
definitions also held for gcc 4.x.  And when I added unit-at-a-time,
the __unused started being taken seriously, and UML libc-side
initcalls were thrown out.

> Why is it that with same compiler, some systems had a problem and some
> did not? is it .config related?

I have no idea.  When Ulrich Drepper first hit this, he and I had the
same base system, same architecture, same toolchain, same config, and
I didn't see it.

I've upgraded since then, so I can't test in the same environment, but
when I add the bug back in such that it hits with gcc 4.3, I get the
crash.

So, this is very mysterious.

> Also I would prefer if the:
>    #define __used __attribute__((__used__))
> would get an #if ((__GNUC__* 100 + __GNUC_MINOR__) >= 303 )
> of its own because other wise this problem will return when
> gcc hits 5. Just as it returned now. 

I don't see the point - this is all wrapped in __GNUC__ == 3 or 4.  As
for gcc 5, linux/compiler has this to say:

#else
# error Sorry, your compiler is too old/not recognized.
#endif

So the kernel totally won't build with gcc 5.

			Jeff

-- 
Work email - jdike at linux dot intel dot com

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