Re: exporting kernel symbols

[kumar M]

Hi Keith,

Thank you for the info. It was very informative.
My problem is funny.
On a freshly installed RedHat 7.1 machine
with 2.4.2-2 kernel,  a 'make modules'
throws up  errors such as  :
----------------------------------------
/usr/src/linux-2.4/include/linux/module.h:173: nondigits in number and not 
hexadecimal
/usr/src/linux-2.4/include/linux/module.h:173: parse error before `62dada05'
/usr/src/linux-2.4/include/linux/module.h:173: 
`inter_module_register_R_ver_str' declared as function returning a function
/usr/src/linux-2.4/include/linux/module.h:173: warning: function declaration 
isn't a prototype
.......................................................

So we do a 'make mrproper' and 'make menuconfig' and
save and exit without any changes to configuration.
Then we rebuild the kernel.
make dep & make modules are done smoothly.

Can you let us know why we should be doing make mrproper
on a system freshly installed  with redhat 7.1(2.4.2-2smp)

Thanks !

Kumar

>From: Keith Owens <[e-mail]>
>To: "kumar M" <[e-mail]>
>CC: [e-mail]
>Subject: Re: exporting kernel symbols
>Date: Mon, 28 Jan 2002 10:37:44 +1100
>
>On Sun, 27 Jan 2002 15:16:10 +0000,
>"kumar M" <[e-mail]> wrote:
> >I am interested in knowing how mangling the name of symbols
> >exported by the kernel to include the checksum of the information related 
>to
> >that symbol is done, whenever MOD VERSIONS
> >is used for building a module. Is there any documentation on the
> >process of the checksum computation, and which portion of the linux
> >sources I need to go through to understand this ?
>
>genksyms.c in the modutils source package[1].  The make dep process
>pre-processes the C sources from each directory feeding the cpp output
>into genksyms.  genksyms calculates a hash for each exported symbol
>based on its type, return values, parameters etc., recursively
>descending parameter types as required.
>
>The resulting hashes are written out as #defines to change foo to
>foo_Rxxxxxxxx.  The defines are read back in when the real compile is
>done, change references to foo into foo_Rxxxxxxxx.  In the kernel the
>original symbols are used but the export list includes the suffix.  In
>modules, external references include the suffix.
>
>In theory if a module refers to a symbol and the hashes for that symbol
>match then the symbol has not changed its ABI and it is safe to load
>the module, even if the kernel and module are from different versions.
>In practice, modversions relies far too much on human processes and is
>prone to false positives.  The hashes can match when the ABI is
>different because of human error[2], especially when people compile
>drivers outside the kernel tree.  Kernel and modutils 2.5 will have a
>completely different method for checking ABI compatibility, if kbuild
>2.5 ever gets in.
>
>[1] http://kernel.org/pub/linux/utils/kernel/modutils/v2.4
>[2] http://prdownloads.sourceforge.net/kbuild/kbuild-2.5-history.tar.bz2
>

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