Re: [PATCH v2 2/3] XENVER_build_id: Provide ld-embedded build-ids

[Ross Lagerwall <ross.lagerwall@citrix.com>]

On 11/06/2015 07:36 PM, Konrad Rzeszutek Wilk wrote:
> From: Martin Pohlack <mpohlack@amazon.de>
>
> The mechanism to get this is via the XENVER_build_id and
> we add a new subsequent sub-command to retrieve the
> binary build-id. The hypercall allows an arbitrary
> size (the buffer and len is provided to the hypervisor).
>
> Note that one can also retrieve the value by 'readelf -h xen-syms'.
>
> For EFI builds we re-use the same build-id that the xen-syms
> was built with.
>
> Note that there are no changes to the XSM files (dummy.c
> and hooks.c) as the priviliged subops fall in the default case.
>
> Since the new sub-ops provides the len parameter in the
> arguments to the hypercall we have to modify libxc to allow
> copying the arguments before the hypercall. We provide a
> new macro that modifies the bounce structure to change
> the direction.
>
snip
> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
> index d4e507a..17a4830 100644
> --- a/xen/arch/x86/Makefile
> +++ b/xen/arch/x86/Makefile
> @@ -109,15 +109,19 @@ $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o

The above invocation of ld also needs to pass "--build-id=sha1".
Otherwise, the first invocation of tools/symbols has 
__note_gnu_build_id_end == __note_gnu_build_id_start, which may cause 
the size of the symbol table to change later when there is actually a 
build id (presumably due to the way it is compressed?) ultimately 
resulting in incorrect values in the symbol table.

>   	$(NM) -pa --format=sysv $(@D)/.$(@F).0 \
>   		| $(BASEDIR)/tools/symbols --sysv --sort >$(@D)/.$(@F).0.S
>   	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0.o
> -	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
> +	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o --build-id=sha1 \
>   	    $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
>   	$(NM) -pa --format=sysv $(@D)/.$(@F).1 \
>   		| $(BASEDIR)/tools/symbols --sysv --sort --warn-dup >$(@D)/.$(@F).1.S
>   	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1.o
> -	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
> +	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o --build-id=sha1 \
>   	    $(@D)/.$(@F).1.o -o $@
>   	rm -f $(@D)/.$(@F).[0-9]*
>

-- 
Ross Lagerwall