Re: [Xen-devel] [PATCH v2] make use of .startof.() and .sizeof.() assembler expressions

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.08.16 at 17:31, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 24/08/16 08:44, Jan Beulich wrote:
>> Section start symbols frequently obscure the actual symbol name living
>> at the start of the section. Eliminate them where they can be replaced
>> by linker resolved .startof.* symbols. (Section end symbols may have
>> the same undesirable effect, but they're less easy to eliminate, as
>> they'd need to be represented by the sum of .startof.<section> and
>> .sizeof.<section>).
>>
>> Along those lines use .sizeof.* where section sizes get calculated
>> from the difference of section and and section start symbols.
>>
>> Note that this would be nice for the build-id section too, but:
>> - The generated (by ld) section names differ between ELF and COFF/PE
>>   (ELF: .note.gnu.build-id; COFF/PE[2.26+]: .buildid), yet we compile
>>   version.c just once (and hence can use only either of the necessary
>>   .startof./.sizeof. forms).
>> - The ELF section name needs to be quoted in the .startof./.sizeof.
>>   expressions, yet that quoting is supported only by gas 2.26+.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Other than Juliens concerns, I am generally -1 so far for this patch.
> 
> I can appreciate the improvement you are trying to make, but this patch
> is using an entirely undocumented feature of gnu LD, with no guarantees
> that the feature won't disappear under our feet.  Were these to become
> formally documented as stable, then that would be fine.

It's been there for years, but I can certainly point out the
undocumentedness to the binutils maintainers. Not that I
expect much to come out of this other than them suggesting
me to write up something.

> It also doesn't cater for the Clang build, which is a hard blocker to
> accepting the patch.

I'll see if I can get a Clang environment set up somehow.

Jan


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