[Crash-utility] Re: linux_banner problem in 2.6.20/Ubuntu

[Dave Anderson]

Alex Sidorenko wrote:

> Hi Dave,
>
> trying the latest crash-4.0-3.20 on the latest Ubuntu/feisty kernel
> 2.6.20-9-generic I have found that live access does not work because of the
> following mismatch:
>
> /proc/version:
> Linux version 2.6.20-9-generic (root at rothera) (gcc version 4.1.2 (Ubuntu
> 4.1.2-0ubuntu3)) #2 SMP Mon Feb 26 03:01:44 UTC 2007
> linux_banner:
> Linux version 2.6.20-9-generic (root at rothera) (gcc version 4.1.2 (Ubuntu
> 4.1.2-0ubuntu3)) #2 SMP Mon Feb 26 03:01:44 UTC 2007 (Ubuntu
> 2.6.20-9.16-generic)
>
> Looking at 2.6.20 sources (as provided in Ubuntu package) we see:
>
> ----------------------------------------------------------------------------------------
> const char linux_banner[] =
>         "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
>         LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION
> #ifdef CONFIG_VERSION_SIGNATURE
>         " (" CONFIG_VERSION_SIGNATURE ")"
> #endif
>         "\n";
>
> const char linux_proc_banner[] =
>         "%s version %s"
>         " (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
>         " (" LINUX_COMPILER ") %s\n";
> ----------------------------------------------------------------------------------------
>
> As a result, these two strings will be different if CONFIG_VERSION_SIGNATURE
> is defined as non-empty string.
>
> The comparison crash uses is (kernel.c):
>
>             if (strlen(kt->proc_version) && !STREQ(buf, kt->proc_version)) {
>                     if (CRASHDEBUG(1)) {
>                             fprintf(fp, "/proc/version:\n%s",
>                                     kt->proc_version);
>                             fprintf(fp, "linux_banner:\n%s\n", buf);
>                     }
>                     goto bad_match;
>
> I tried to fix the problem by replacing STREQ with STRNEQ. Unfortunately, this
> does not work as both strings are LF-terminated. So I had to use
>
> --- kernel.c.orig       2007-02-21 15:52:01.000000000 -0500
> +++ kernel.c    2007-03-11 08:20:38.468024104 -0400
> @@ -498,7 +498,8 @@
>                 error(WARNING, "cannot read linux_banner string\n");
>
>         if (ACTIVE()) {
> -               if (strlen(kt->proc_version) && !STREQ(buf, kt->proc_version))
> {
> +               int cmplen = strlen(kt->proc_version)-1;
> +               if (cmplen>0 && strncmp(buf, kt->proc_version, cmplen) != 0) {
>                                 if (CRASHDEBUG(1)) {
>                                 fprintf(fp, "/proc/version:\n%s",
>                                         kt->proc_version);
>
> Please note that this seems to be Ubuntu-specific problem - the generic
> 2.6.20.2 has linux_banner definition without CONFIG_VERSION_SIGNATURE.
> Searching Google for "linux CONFIG_VERSION_SIGNATURE" I can see only results
> related to Ubuntu.
>
> Regards,
> Alex

Hi Alex,

This looks fine -- queued for the next release.

Thanks,
  Dave