Re: [PATCH] Makefile: Use relative paths for debugging symbols.

[Vagrant Cascadian <vagrant@reproducible-builds.org>]

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On 2022-08-28, Rasmus Villemoes wrote:
> On 26/08/2022 22.59, Tom Rini wrote:
>> On Thu, Aug 18, 2022 at 10:31:34AM -0700, Vagrant Cascadian wrote:
>> 
>>> From: Vagrant Cascadian <vagrant@reproducible-builds.org>
>>>
>>> The KBUILD_CFLAGS and KBUILD_AFLAGS variables are adjusted to use
>>> -ffile-prefix-map and --debug-prefix-map, respectively, to use
>>> relative paths for occurrences of __FILE__ and debug paths.
>>>
>>> This enables reproducible builds regardless of the absolute path to
>>> the build directory:
>>>
>>>   https://reproducible-builds.org/docs/build-path/
>>>
>>> Signed-off-by: Vagrant Cascadian <vagrant@reproducible-builds.org>
>>> Acked-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
>> 
>> This needs some sort of clang check and then perhaps different flag
>> used? How does the linux kernel handle this?
>
> Well, interestingly it seems that the kernel doesn't do anything like
> this for debug info, they only apply the -fmacro-prefix-map. Which one
> should probably raise with them at some point.
>
> It seems we're not actually calling gas directly, but always invokes
> $(CC) whatever that may be to compile assembler files. So I think the
> right fix is to simply pass the same -ffile-prefix-map in both
> KBUILD_CFLAGS as in KBUILD_AFLAGS - and if there's some variable that
> ends up being included in both automatically, then just adding it there
> should do the trick.

I tried just adding -ffile-prefix-map and that helped, but was not
sufficient to solve the reproducibility issues. It also needs the
--debug-prefix-map to make it the assembly code build reproducibly.

Though I guess I didn't try adding -ffile-prefix-map to KBUILD_AFLAGS,
now that I think about it... will test that too, thanks!


live well,
  vagrant

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