Re: /proc/kallsyms and symbol size

From: Stephane Eranian
Date: Wed Sep 26 2007 - 02:51:10 EST


On Tue, Sep 25, 2007 at 05:21:06PM +0100, Paulo Marques wrote:
> Stephane Eranian wrote:
> >Hello,
> Hi, Stephane
> >Many monitoring tools use /proc/kallsyms to build a symbol table for the
> >kernel.
> >This technique has the advantage that it does not require root privileges,
> >nor
> >an up-to-date /boot/, nor a decompressed kernel in /boot.
> >
> >The problem is that /proc/kallsyms does not report the size of the symbols.
> >Yet, the information is available in the kernel as it is used by functions
> >such as __print_symbol(). Having the size is useful to correlate the address
> >obtained
> >is a sample with a symbol name. Most tools use an approximation which
> >assumes
> >symbols are contiguous to estimate the size.
> That is actually what the kernel does internally, too. It does not keep
> the size of the symbol, but tries to guess it from the address of the
> next non-aliased symbol.
> Since the addresses are sorted, this works fine most of the time. This
> is done to reduce the size used by the symbol table in the running kernel.
> Just take a look at "get_symbol_pos" in kernel/kallsyms.c and
> "get_ksymbol" in kernel/module.c to see exactly how this is done
Ok. Then we cannot really do better.

Also thank you for alerting me on the aliased symbols. I have modified
my user code to only keep the first symbol.

Thanks for you help.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at