llvm dev - Jan 2017 - Linking Linux kernel with LLD

On Fri, Jan 20, 2017 at 12:44 PM, Sean Silva <chisophugis at gmail.com>
wrote:
>
>
> On Fri, Jan 20, 2017 at 8:35 AM, George Rimar via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Dmitry,
>>
>> thanls for sharing. Few comments/questions below:
>>
>> >Here is the list of modifications I had to do in order to link the
>> kernel (I have used llvmlinux with clang and mainline with gcc, the
>> >results are similar):
>> >
>> >1. LLD patches:
>>  > - D28094 (Implemented support for R_386_PC8/R_386_8 relocations)
>>
>> Do you remember where it was used ?
>>
>> >5. In arch/x86/kernel/vmlinux.lds.S commented out the
"CONSTRUCTORS",
>> because LLD doesn't support it.
>>
>> It is https://reviews.llvm.org/D28951. CONSTRUCTORS can be just
removed,
>> they do nothing for ELF.
>>
>> >6. In arch/x86/boot/setup.ld replaced 5*512 with precalculated
value of
>> 2560 because it doesn't seem that LLD supports math inside
>ASSERT in
>> linker scripts.
>>
>> It is actually not relative with ASSERT. LLD does not support
"symbol >> 5*6", but accepts "symbol = 5 * 6"
currently.
>> Not sure what is easy fix here.
>>
>
> I'm not sure if it is easy, but I think that it's clear that the
> linkerscript lexer needs to be improved. I think that is the source of the
> problems with `*(.apicdrivers);` as well.
>
Actually, quickly staring at the code, the `*(.apicdrivers);` seems like it
will be lexed  correctly.

-- Sean Silva

> This is not the first bug related to lexing that we have run into (e.g.
> lexing `.=` as a single token is the cause of https://llvm.org/bugs/show_
> bug.cgi?id=31128 ).
>
> -- Sean Silva
>
>
>>
>> >Finally the kernel was built and it obviously didn't run (only
printed
>> out "No setup signature found..." but this is some result as
well).
>> >Probably, the result could be better if the --emit-relocs option
didn't
>> fail and CONSTRUCTORS were supported. I really don't know what
>to do about
>> the assertion that I have commented out.
>>
>> I updated patch for --emit-relocs, now they do not fail:
>> https://reviews.llvm.org/D28612
>> It looks to be important feature for self relocations, so it is not
>> surprising it did not run without :)
>>
>> George.
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
>
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>I'm not sure if it is easy, but I think that it's clear that the
linkerscript lexer needs to be improved. I think that is the source of the
>problems with `*(.apicdrivers);` as well. This is not the first bug related
to lexing that we have run into (e.g. lexing `.=` as a single >token is the
cause of https://llvm.org/bugs/show_bug.cgi?id=31128 ).
>
>-- Sean Silva
PR31128? seems to be not an issue. Both gold and bfd do not accept '.='.
So it seems the only known issue we have is about math expressions like "x
= 5*4",
I am going to look again how to fix that.

George.?

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Our tokenizer recognize

  [A-Za-z0-9_.$/\\~=+[]*?\-:!<>]+

as a token. gold uses more complex rules to tokenize. I don't think we need
that much complex rules, but there seems to be room to improve our
tokenizer. In particular, I believe we can parse the Linux's linker script
by changing the tokenizer rules as follows.

  [A-Za-z_.$/\\~=+[]*?\-:!<>][A-Za-z0-9_.$/\\~=+[]*?\-:!<>]*

or

  [0-9]+

On Mon, Jan 23, 2017 at 9:25 AM, George Rimar via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> >I'm not sure if it is easy, but I think that it's clear that
the
> linkerscript lexer needs to be improved. I think that is the source of the
> >problems with `*(.apicdrivers);` as well. This is not the first bug
> related to lexing that we have run into (e.g. lexing `.=` as a single
> >token is the cause of https://llvm.org/bugs/show_bug.cgi?id=31128 ).
> >
> >-- Sean Silva
>
> PR31128​ seems to be not an issue. Both gold and bfd do not accept
'.='.
> So it seems the only known issue we have is about math expressions like
"x
> = 5*4",
> I am going to look again how to fix that.
>
> George.​
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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