branch-1_4 debian bug 154053 - ENOSYS in sigstack

[Eric Blake]

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http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=154053;archive=yes (and
also CVS head's TODO) reports:

> m4: sigstack: Function not implemented
>
> I did a little searching around on the web (looked for "sigstack not
> found" with Google) and found some interesting discussions about M4
> generating this kind of error when built with 2.2 header files and used
> on 2.0.x kernels (sigstack does not exist in 2.0 kernels, and M4 instead
> of paying attention to ENOSYS returned by the call and trying to do
> something else, just fails).

Seeing as how 2.0 kernels are rare these days, this is probably too
little, too late.  However, I agree that ENOSYS is different from other
errors, and that m4 should just gracefully continue without stack overflow
detection (as it does when sigstack is not found during configuration).  I
don't know if it warrants a NEWS entry.

2006-08-03  Eric Blake  <address@hidden>

        * src/stackovf.c (setup_stackovf_trap): Gracefully avoid stack
        overflow detection when sigstack exists but is not implemented.
        Fixes debian bug 154053.
        * THANKS: Updated.
        Reported by David Perlin.

- --
Life is short - so eat dessert first!

Eric Blake             address@hidden
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Index: src/stackovf.c
===================================================================
RCS file: /sources/m4/m4/src/stackovf.c,v
retrieving revision 1.1.1.1.2.4
diff -u -p -r1.1.1.1.2.4 stackovf.c
--- src/stackovf.c      28 Jul 2006 20:39:37 -0000      1.1.1.1.2.4
+++ src/stackovf.c      3 Aug 2006 12:18:08 -0000
@@ -346,7 +346,16 @@ Error - Do not know how to set up stack-
     ss.ss_sp = xmalloc ((unsigned) ss.ss_size);
     ss.ss_flags = 0;
     if (sigaltstack (&ss, NULL) < 0)
-      error (EXIT_FAILURE, errno, "sigaltstack");
+      {
+       /* Oops - sigaltstack exists but doesn't work.  We can't
+          install the overflow detector, but should gracefully treat
+          it as though sigaltstack doesn't exist.  For example, this
+          happens when compiled with Linux 2.1 headers but run
+          against Linux 2.0 kernel.  */
+       if (errno == ENOSYS)
+         return;
+       error (EXIT_FAILURE, errno, "sigaltstack");
+      }
   }
 
 #elif HAVE_SIGSTACK
@@ -358,7 +367,16 @@ Error - Do not know how to set up stack-
     ss.ss_sp = stackbuf + SIGSTKSZ;
     ss.ss_onstack = 0;
     if (sigstack (&ss, NULL) < 0)
-      error (EXIT_FAILURE, errno, "sigstack");
+      {
+       /* Oops - sigstack exists but doesn't work.  We can't install
+          the overflow detector, but should gracefully treat it as
+          though sigstack doesn't exist.  For example, this happens
+          when compiled with Linux 2.1 headers but run against Linux
+          2.0 kernel.  */
+       if (errno == ENOSYS)
+         return;
+       error (EXIT_FAILURE, errno, "sigstack");
+      }
   }
 
 #else /* not HAVE_SIGSTACK */