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Re: PATCH: Fix linker plugin support for gnu linker


On Sat, Jan 8, 2011 at 7:44 AM, Richard Sandiford
<rdsandiford@googlemail.com> wrote:
> "H.J. Lu" <hjl.tools@gmail.com> writes:
>> On Sat, Jan 8, 2011 at 6:46 AM, Richard Sandiford
>> <rdsandiford@googlemail.com> wrote:
>>> "H.J. Lu" <hjl.tools@gmail.com> writes:
>>>> On Sat, Jan 8, 2011 at 4:10 AM, Richard Sandiford
>>>> <rdsandiford@googlemail.com> wrote:
>>>>> "H.J. Lu" <hongjiu.lu@intel.com> writes:
>>>>>> This patch fixes linker plugin support for gnu linker with 2 stage
>>>>>> linking and supports mixed LTO objects:
>>>>>>
>>>>>> http://www.kernel.org/pub/linux/devel/gcc/lto/mixed-IR/mixed-IR.pdf
>>>>>>
>>>>>> Any objections?
>>>>>
>>>>> One problem with the patch as written is that it doesn't cope with
>>>>> the kind of embedded setup in which the startup file is specified
>>>>> in a linker script. ?E.g. on mipsisa64-elf, GCC doesn't know what
>>>>> system you're targetting, and therefore doesn't what startup files or
>>>>> board-specific libraries are needed. ?You instead link with something
>>>>> like -Tidt64.ld. ?idt64.ld then contains:
>>>>>
>>>>> STARTUP(crt0.o)
>>>>>
>>>>> -T options are parsed immediately in-place, and don't show up in the
>>>>> cmdline_options. ?Things like STARTUP don't either. ?This means that
>>>>> crt0.o is dropped by the second stage link.
>>>>>
>>>>> The handling of -T also means that the system libraries:
>>>>>
>>>>> GROUP(-lc -lidt -lgcc)
>>>>>
>>>>> don't show up in the second link. ?However, that brings up a broader
>>>>> question (which might already have been answered, sorry). ?The current
>>>>> process -- that is, the process before the 2-stage patch -- seems to
>>>>> rely on the GCC driver passing the equivalent of:
>>>>>
>>>>> ?-pass-through=-lgcc -pass-through=-lc -pass-through=-lgcc
>>>>>
>>>>> to the plugin. ?But on targets like mipsisa64-elf, GCC doesn't know
>>>>
>>>> hjl/lto-mixed branch ignores ?-pass-through=XXX passed from gcc driver.
>>>
>>> Right, that's what I meant. ?The fact that the 2-pass link doesn't
>>> need those options means that it would solve the problem for free.
>>> But at the moment it doesn't work because it ignores the linker script's
>>> GROUP as well.
>>
>> You can pass -Wl,--verbose to gcc to see exactly what are passed to
>> stage 2 linking:
>>
>> Stage 2 command line:
>> ? /usr/lib/../lib/crt1.o /usr/lib/../lib/crti.o
>> /usr/gcc-4.6/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/32/crtbegin.o
>> /tmp/ccmzgIMd.ltrans0.ltrans.o --no-whole-archive
>> /usr/gcc-4.6/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/32/libgcc.a
>> /usr/gcc-4.6/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/../../../../lib/libgcc_s.so
>> /usr/lib/../lib/libc.so --no-whole-archive
>> /usr/gcc-4.6/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/32/libgcc.a
>> /usr/gcc-4.6/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/../../../../lib/libgcc_s.so
>> /usr/gcc-4.6/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/32/crtend.o
>> /usr/lib/../lib/crtn.o
>
> Yeah, that's what I was doing. ?crt0.o and the GROUP files are not listed.
>
> The linker command line is:
>
> ? /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/libexec/gcc/mipsisa64-elf/4.6.0/liblto_plugin.so -plugin-opt=/export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/libexec/gcc/mipsisa64-elf/4.6.0/lto-wrapper -plugin-opt=-fresolution=/tmp/ccyO6BXX.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc -EB -o /tmp/foo /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crti.o /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtbegin.o -L/export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0 -L/export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/../../../../../H-x86_64-unknown-linux-gnu/mipsisa64-elf/lib /tmp/ccRbTLAW.o -v -M --verbose -lgcc -lgcc /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtend.o /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtn.o -T idt64.ld
>
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/../../../../../H-x86_64-unknown-linux-gnu/mipsisa64-elf/lib/crt0.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crti.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtbegin.o
> LOAD /tmp/ccRbTLAW.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtend.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtn.o
> START GROUP
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/../../../../../H-x86_64-unknown-linux-gnu/mipsisa64-elf/lib/libc.a
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/../../../../../H-x86_64-unknown-linux-gnu/mipsisa64-elf/lib/libidt.a
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a
> END GROUP
> [...]
> Stage 2 command line:
> ?/export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crti.o /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtbegin.o /tmp/cctWDG0U.ltrans0.ltrans.o --no-whole-archive /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a --no-whole-archive /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtend.o /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtn.o
> [...]
> OUTPUT(/tmp/foo elf32-bigmips)
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crti.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtbegin.o
> LOAD /tmp/cctWDG0U.ltrans0.ltrans.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/libgcc.a
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtend.o
> LOAD /export/richards/usr/gcc/H-x86_64-unknown-linux-gnu/lib/gcc/mipsisa64-elf/4.6.0/crtn.o/export/richards/usr/src/H-x86_64-unknown-linux-gnu/bin/mipsisa64-elf-ld: warning: cannot find entry symbol _start; defaulting to 0000000080020000
> /tmp/cctWDG0U.ltrans0.ltrans.o: In function `main':
> (.text+0x2c): undefined reference to `abort'
> /tmp/cctWDG0U.ltrans0.ltrans.o: In function `main':
> (.text+0x38): undefined reference to `exit'
> collect2: ld returned 1 exit status
>
> Note how crt0.o and the group are missing from the second LOAD list.
>
>> I just need to handle STARTUP properly.
>
> And GROUP. :-)

and INPUT.

>
>> If you can provide a native testcase on Linux/x86-64, I will fix it.
>
> Sorry, I don't have time to reproduce this on x86_64. ?I'm just trying
> to provide feeback to the patch submission.
>

I may not have time to create testcases and fix them. I
would appreciate someone can open bug reports with
native testcases on Linux/x86. It will help me a lot.

Thanks.

-- 
H.J.


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