[PATCH] D49513: [ELF] gdb-index: don't remove .debug_gnu_pub{names, types} in -r mode

Tue Jul 24 12:32:52 PDT 2018

Sorry, might've been a bit imprecise.

Simple object files start with one CU in the debug_info section and one
debug_gnu_pubnames section - my concern was that the pubnames section might
not specify which CU it's about. My mistake though, it does. So ld -r'ing
two objects together, creating one gnu_pubnames section with the two chunks
of pubnames from the two input object files is fine - because the chunks
specify which CU they correspond to - there's no information loss there.

I mean, if you went far and ld -r half your objects together, you're going
to have huge pubnames sections and you might wish that your linker had
produced a fancy, faster, more compact index in that object file - but I
don't think that's really a problem we need to solve today (or until
someone really decides that's an important scenario for them).

On Tue, Jul 24, 2018 at 10:32 AM Rui Ueyama <ruiu at google.com> wrote:

> I believe lld recognizes only the first .gnu_pubnames section and ignore
> other sections with the same name in the same object file, but I might be
> wrong.
>
> On Mon, Jul 23, 2018 at 5:03 PM David Blaikie <dblaikie at gmail.com> wrote:
>
>> This might not be especially useful - the gnu_pubnames sections don't
>> describe which CU they are for (if I recall correctly), so once you've got
>> multiple CUs in a single object file (admittedly, this happens in LTO too,
>> adn I'm not sure how that's handled) it might not be terribly useful. I'm
>> not sure what lld's gdb-index does when consuming an object with multiple
>> CUs in it, for example.
>>
>> On Wed, Jul 18, 2018 at 3:03 PM Fangrui Song via Phabricator via
>> llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>>> MaskRay updated this revision to Diff 156160.
>>> MaskRay added a comment.
>>>
>>> .
>>>
>>>
>>> Repository:
>>>   rLLD LLVM Linker
>>>
>>> https://reviews.llvm.org/D49513
>>>
>>> Files:
>>>   ELF/Driver.cpp
>>>   test/ELF/driver.test
>>>
>>>
>>> Index: test/ELF/driver.test
>>> ===================================================================
>>> --- test/ELF/driver.test
>>> +++ test/ELF/driver.test
>>> @@ -35,31 +35,35 @@
>>>  # RUN: not ld.lld -r --gc-sections %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR3 %s
>>>  # ERR3: -r and --gc-sections may not be used together
>>>
>>> +## Attempt to use -r and --gdb-index together
>>> +# RUN: not ld.lld -r --gdb-index %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR4 %s
>>> +# ERR4: -r and --gdb-index may not be used together
>>> +
>>>  ## Attempt to use -r and --icf together
>>> -# RUN: not ld.lld -r --icf=all %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR4 %s
>>> -# ERR4: -r and --icf may not be used together
>>> +# RUN: not ld.lld -r --icf=all %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR5 %s
>>> +# ERR5: -r and --icf may not be used together
>>>
>>>  ## Attempt to use -r and -pie together
>>> -# RUN: not ld.lld -r -pie %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR5 %s
>>> -# ERR5: -r and -pie may not be used together
>>> +# RUN: not ld.lld -r -pie %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR6 %s
>>> +# ERR6: -r and -pie may not be used together
>>>
>>>  ## Attempt to use -shared and -pie together
>>> -# RUN: not ld.lld -shared -pie %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR6 %s
>>> -# ERR6: -shared and -pie may not be used together
>>> +# RUN: not ld.lld -shared -pie %t -o %tfail 2>&1 | FileCheck
>>> -check-prefix=ERR7 %s
>>> +# ERR7: -shared and -pie may not be used together
>>>
>>>  ## "--output=foo" is equivalent to "-o foo".
>>> -# RUN: not ld.lld %t --output=/no/such/file 2>&1 | FileCheck
>>> -check-prefix=ERR7 %s
>>> -# ERR7: cannot open output file /no/such/file
>>> +# RUN: not ld.lld %t --output=/no/such/file 2>&1 | FileCheck
>>> -check-prefix=ERR8 %s
>>> +# ERR8: cannot open output file /no/such/file
>>>
>>>  ## "-output=foo" is equivalent to "-o utput=foo".
>>> -# RUN: not ld.lld %t -output=/no/such/file 2>&1 | FileCheck
>>> -check-prefix=ERR8 %s
>>> -# ERR8: cannot open output file utput=/no/such/file
>>> +# RUN: not ld.lld %t -output=/no/such/file 2>&1 | FileCheck
>>> -check-prefix=ERR9 %s
>>> +# ERR9: cannot open output file utput=/no/such/file
>>>
>>> -# RUN: not ld.lld %t -z foo 2>&1 | FileCheck -check-prefix=ERR9 %s
>>> -# ERR9: unknown -z value: foo
>>> +# RUN: not ld.lld %t -z foo 2>&1 | FileCheck -check-prefix=ERR10 %s
>>> +# ERR10: unknown -z value: foo
>>>
>>> -# RUN: not ld.lld %t -z max-page-size 2>&1 | FileCheck
>>> -check-prefix=ERR10 %s
>>> -# ERR10: unknown -z value: max-page-size
>>> +# RUN: not ld.lld %t -z max-page-size 2>&1 | FileCheck
>>> -check-prefix=ERR11 %s
>>> +# ERR11: unknown -z value: max-page-size
>>>
>>>  .globl _start
>>>  _start:
>>> Index: ELF/Driver.cpp
>>> ===================================================================
>>> --- ELF/Driver.cpp
>>> +++ ELF/Driver.cpp
>>> @@ -294,6 +294,8 @@
>>>        error("-r and -shared may not be used together");
>>>      if (Config->GcSections)
>>>        error("-r and --gc-sections may not be used together");
>>> +    if (Config->GdbIndex)
>>> +      error("-r and --gdb-index may not be used together");
>>>      if (Config->ICF)
>>>        error("-r and --icf may not be used together");
>>>      if (Config->Pie)
>>>
>>>
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>>
>>
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