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Re: rpctrace / libpager / signal preemptor

From: Brent W. Baccala
Subject: Re: rpctrace / libpager / signal preemptor
Date: Wed, 30 Nov 2016 22:47:09 -1000

On Wed, Nov 16, 2016 at 9:05 AM, Samuel Thibault <samuel.thibault@gnu.org> wrote:
Samuel Thibault, on Wed 16 Nov 2016 19:50:07 +0100, wrote:
> Samuel Thibault, on Wed 16 Nov 2016 19:46:52 +0100, wrote:
> > The attached testcase does get the faulting address.
> And the attached testcase doesn't.

And is fixed by the attached patch, could you try it?

OK, I've finally tested this patch!

It took me a while.  I had a lot of problems building the glibc package, so I finally stopped trying to build the package and just built the library with the intent of injecting it into ext2fs using LD_LIBRARY_PATH.  It took me a while to figure out that settrans clobbers the environment, and that bug I reported about the /proc environ files returning I/O errors certainly didn't help.  I finally got the translator loading the library using a trick that I want to document:

    settrans -a mnt /usr/bin/env LD_LIBRARY_PATH=/root/lib /hurd/ext2fs ramdisk

The patch works, but is incomplete.  Samuel's test programs attempt to access unmapped memory addresses, which generate KERN_MEMORY_FAILURE, but ext2fs attempts to access mapped addresses back by a memory manager returning faults, which generates KERN_MEMORY_ERROR, so we also need this:

--- sysdeps/mach/hurd/i386/exc2signal.c~ 2016-11-09 20:03:52.000000000 -1000
+++ sysdeps/mach/hurd/i386/exc2signal.c  2016-11-30 01:54:02.000000000 -1000
@@ -40,6 +40,7 @@
+       case KERN_MEMORY_ERROR:
          *signo = SIGSEGV;
          detail->code = posix ? SEGV_MAPERR : detail->exc_subcode;

That, along with the other patches, seems to produce an ext2fs that can handle disk full conditions without dying!

It still exhibits some weird behavior - creating directory entries for the files that it doesn't have the space for.

Do we have any kind of a test suite for hurd?  This seems like a nice test - mount a ramdisk and fill it up.  We've uncovered a number of bugs trying to do that.


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