[llvm-dev] [ThinLTO] static library failure with object files with the same name

Mehdi AMINI via llvm-dev llvm-dev at lists.llvm.org
Mon Sep 11 20:25:03 PDT 2017

Hi Johan,

2017-09-11 14:21 GMT-07:00 Johan Engelen <jbc.engelen at gmail.com>:

> On Fri, Sep 8, 2017 at 9:04 PM, Johan Engelen <jbc.engelen at gmail.com>
> wrote:
>> On Thu, Sep 7, 2017 at 5:44 PM, Mehdi AMINI <joker.eph at gmail.com> wrote:
>>> Hi Johan,
>>> ld64 only calls functions from llvm/include/llvm-c/lto.h  (defined
>>> in llvm/tools/lto/lto.cpp)
>>> For instance ThinLTOCodeGenerator::addModule is called
>>> through thinlto_codegen_add_module().
>>> Apple hasn't released the code for ld64 in Xcode 9 yet, did you check if
>>> it is fixed in Xcode 9?
>>> (I think I remember fixing it in ld64 but I'm not totally sure...).
>> I haven't tried with Xcode 9.
>>> From what I can see with Xcode 8.2, the linker just passes the file name
>>> (prefixed with the archive name): https://github.com/michaelweis
>>> er/ld64/blob/master/src/ld/parsers/lto_file.cpp#L546
>>> (original here: https://opensource.apple.com/source/ld64/ld64-274.2/sr
>>> c/ld/parsers/lto_file.cpp.auto.html )
>>> We could workaround this in ThinLTOCodeGenerator by adding a incremental
>>> suffix to every new buffer. Something like this diff:
>> I was assuming that we do want to assert/error on calling addModule with
>> the exact same module twice? Otherwise your diff is nice, thanks.
> Hi Mehdi,
>   Can you advise me?
> Is it OK to not error upon the exact same module being added twice? (and
> thus your patch would be good)
It is a matter of API contract, so I'm not sure I perceive a clear
right/wrong here. If we want to enforce an API contract on the caller's
responsibility to provide a unique ID, then the assert may be OK (however
we disable assertions in production and it means random crashes which isn't
super user-friendly).
On the other hand my patch here was trying to be resilient to API misuse
for "little cost".

Note that the plan was that this API (and the ThinLTOCodegenerator.cpp)
should just die, but unfortunately I haven't had time to work on the
replacement (a C binding for the new LTO API).

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