Hi Dave,

I can't open vmcore for 2.6.20-rc2 vanilla kernel with crash. I am using
latest crash version 4.0-3.16.

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WARNING: invalid linux_banner pointer: 756e694c
crash: vmlinux and vmcore do not match!
 

It has to do with how the linux_banner symbol is declared.  The crash code
in question does this:
 

        if (!(sp = symbol_search("linux_banner")))
                error(FATAL, "linux_banner symbol does not exist?\n");
        else if (sp->type == 'R')
                linux_banner = symbol_value("linux_banner");
        else
                get_symbol_data("linux_banner", sizeof(ulong), &linux_banner);

        if (!IS_KVADDR(linux_banner))
                error(WARNING, "invalid linux_banner pointer: %lx\n",
                        linux_banner);

Up until 2.6.20-rc2 (apparently), if the linux_banner symbol
was in the readonly section ('R'), the string data was located
at the address of the linux_banner symbol.  Otherwise, the
linux_banner symbol contained the address of the string data.

In your kernel, what does "nm -Bn vmlinux | grep linux_banner" show?
Maybe 'r' instead of 'R'?

In any case, it should be easy enough to deal with, because you
can see the string data is at the location of the linux_banner
symbol:

> WARNING: invalid linux_banner pointer: 756e694c

and that's the string data instead of a pointer to the string
data:

  crash> ascii 756e694c
  756e694c: Linu
  crash>

Dave