From: Collin Funk <collin.funk1@gmail.com>
Date: Fri, 19 Sep 2025 23:59:19 GMT
Subject: Re: [PATCH v2 02/18] make: add -fPIE flag
Message-ID: <87plbmyox4.fsf@gmail.com>
In-Reply-To: <xmqqa52qypo8.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> writes:

> Ezekiel Newren <ezekielnewren@gmail.com> writes:
>
>> On Fri, Sep 19, 2025 at 2:07 PM Junio C Hamano <gitster@pobox.com> wrote:
>>>
>>> Ezekiel Newren <ezekielnewren@gmail.com> writes:
>>>
>>> > I was trying to get the rust compiler to link against libgit.a. Both
>>> > Meson and Makefile produce libgit.a. No changes were to meson.build
>>> > were necessary for that to work, but but with Makefile I would get
>>> > errors like:
>>> > relocation R_X86_64_32 against `.rodata' can not be used when making a
>>> > PIE object; recompile with -fPIE
>>>
>>> This sounds like a workaround that is somewhat platform and compiler
>>> specific limitation, at least to me.  Does this need to be conditional
>>> and if so on what?
>>
>> I don't know, but I have another question to add to yours. Why does
>> Make need -fPIE in order for the Rust compiler to link against
>> libgit.a created by Make, when Meson doesn't seem to specify PIE
>> anywhere and yet the Rust compiler can work with Meson's libgit.a
>> output?
>
> I do not know what the build procedure using meson exactly does to
> create a library archive.  On the Make side, we do not compile for
> position independence, and don't do anything other than bog standard
> "ar rcs".  Patrick, any hint?

Not too familiar with Rust, but looks like the answer is here [1].
Specificially, this part:

    pic - fully relocatable position independent code, machine
    instructions need to use relative addressing modes. Equivalent to
    the "uppercase" -fPIC or -fPIE options in other compilers, depending
    on the produced crate types. This is the default model for majority
    of supported targets.

Collin

[1] https://doc.rust-lang.org/rustc/codegen-options/index.html#relocation-model