Re: [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: Fix duplicate symbol

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 25 May 2017 at 11:06, Laszlo Ersek <lersek@redhat.com> wrote:
> On 05/25/17 19:38, Kinney, Michael D wrote:
>> Laszlo,
>>
>> I think the equivalent flag for GCC builds is --whole-archive.
>>
>> I tried adding that flag to DLINK_FLAGS in GCC5, and I get the
>> following error building OVMF from edk2/master with
>> -D SOURCE_DEBUG_ENABLE set.
>>
>> DxeLoad.obj (symbol from plugin): In function `InstallIplPermanentMemoryPpis':
>> (.text+0x0): multiple definition of `mMemoryDiscoveredNotifyList'
>> SecPeiDebugAgentLib.obj (symbol from plugin):(.text+0x0): first defined here
>> collect2: error: ld returned 1 exit status
>
> Great find! That's the error message we should get.
>
> Unfortunately, after reading the "ld" manual on "--whole-archive", it
> seems that the complete object files will actually be copied into the
> resultant binary, even if several of their symbols will remain unused. I
> think that's quite sub-optimal. (I haven't verified this though.) What
> we'd like to get is (a) the full verification at link time, and (b)
> inclusion of *only* those symbols that are actually necessary.
>
> In your testing, when you build OVMF with and without "--whole-archive",
> do you see a difference in, say, the DXEFV footprint, when the build
> completes?
>
> (If so, then I wonder if we should add "--whole-archive" only to the
> NOOPT build... Not sure.)
>

I haven't tried, but I would expect --gc-sections to deal with the
unused objects.

>> Visual Studio 2015 Update 2 has also added a new linker flag called
>> /WHOLEARCHIVE.  I am working on evaluating that flag to see if it
>> catches the same issue.
>
> Thanks!
> Laszlo
>
>>> -----Original Message-----
>>> From: Laszlo Ersek [mailto:lersek@redhat.com]
>>> Sent: Thursday, May 25, 2017 9:09 AM
>>> To: Kinney, Michael D <michael.d.kinney@intel.com>; Ard Biesheuvel
>>> <ard.biesheuvel@linaro.org>; Andrew Fish (afish@apple.com) <afish@apple.com>
>>> Cc: Wu, Hao A <hao.a.wu@intel.com>; edk2-devel@lists.01.org; Fan, Jeff
>>> <jeff.fan@intel.com>
>>> Subject: Re: [edk2] [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: Fix duplicate
>>> symbol
>>>
>>> On 05/25/17 03:47, Kinney, Michael D wrote:
>>>> Andrew,
>>>>
>>>> I think I have found an alternate fix for this XCODE5 specific
>>>> build failure.  Since there appears to be a difference in the
>>>> linker behavior between MSFT/GCC/XCODE tool chains, I reviewed
>>>> the 'ld' command line options used in XCODE5 tool chain in
>>>> tools_def.txt.
>>>>
>>>> There is a flag set call '-all_load'.  The description of this
>>>> flag is 'Loads all members of static archive libraries.'.
>>>>
>>>> I tried removing this flag from the XCODE5 specific SLINK_FLAGS
>>>> and DLINK_FLAGS statements in tools_def.txt, and the duplicate
>>>> symbol build failure is no longer present.  I am able to build
>>>> and boot OVMF with XCODE5 with -D SOURCE_DEBUG_ENABLE flag set.
>>>>
>>>> This seems to make XCODE5 linker behavior match the MSFT and GCC
>>>> linker behavior.
>>>>
>>>> Do you know why '-all_load' is used in XCODE5 and what impacts
>>>> there may be from removing it?
>>>
>>> Please don't remove -all_load from there; instead we should figure out
>>> if the same can be brought to MSFT and GCC.
>>>
>>> The error message that XCODE5 emitted caught a real bug (undefined
>>> behavior according to ISO C, see my previous email), and so we should
>>> keep that detection enabled (we should even extend it to other
>>> toolchains, if that's possible).
>>>
>>> As for docs, I found this:
>>>
>>> http://www.manpages.info/macosx/ld.1.html
>>>
>>>> -all_load
>>>>     Loads all members of static archive libraries. This option does
>>>>     not apply to dynamic shared libraries.
>>>
>>>
>>> Thanks
>>> Laszlo
>