Re: [Xen-devel] [PATCH v6 01/15] x86: properly calculate ELF end of image address

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Sep 12, 2016 at 10:18:16PM +0200, Daniel Kiper wrote:
> Currently ELF end of image address is calculated using first line from
> "nm -nr xen/xen-syms" output. However, today usually it contains random
> symbol address not related to end of image in any way. So, it looks

Weird. The -n says:

"  -n
       -v
       --numeric-sort
           Sort symbols numerically by their addresses, rather than 
alphabetically by their names.
"

And you are right. It is ignoring it:

[konrad@char xen]$ nm -nr xen/xen-syms| sort | head -1
ffff82d080000000 T __image_base__
[konrad@char xen]$ nm -nr xen/xen-syms | head -1
ffff82d08033d000 B efi

[konrad@char xen]$ nm -nr xen/xen-syms| sort | tail -5
ffff82d08033cb00 B _end
ffff82d08033cb00 B __per_cpu_data_end
ffff82d08033d000 B __2M_rwdata_end
ffff82d08033d000 B efi
                 U _GLOBAL_OFFSET_TABLE_

> that for years that stuff have been working just by lucky coincidence.
> Hence, it have to be changed to something more reliable. So, let's take
> ELF end of image address by reading _end symbol address from nm output.
> 
> Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> ---
>  xen/arch/x86/Makefile |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
> index d3875c5..a4fe740 100644
> --- a/xen/arch/x86/Makefile
> +++ b/xen/arch/x86/Makefile
> @@ -91,7 +91,7 @@ endif
>  
>  $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
>       ./boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TARGET) 0x100000 \
> -     `$(NM) -nr $(TARGET)-syms | head -n 1 | sed -e 's/^\([^ ]*\).*/0x\1/'`
> +             `$(NM) -nr $(TARGET)-syms | awk '$$3 == "_end" {print "0x"$$1}'`
>  

Something is off with your tabs/spaces.


I would also modify the arch/x86/xen.lds.S and put a comment
around _end = .; to mention this dependency - in case somebody adds some 
extra things after _end.


>  .PHONY: tests
>  tests:
> -- 
> 1.7.10.4
> 

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