[Crash-utility] linux_banner problem in 2.6.20/Ubuntu

[Alex Sidorenko]

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