Re: [Buildroot] [RFC PATCH 3/3] package/llvm-project: reduce the build size of llvm

From: "Alex Bennée" <alex.bennee@linaro.org>
To: Romain Naour <romain.naour@smile.fr>
Cc: buildroot@buildroot.org,  Joseph Kogut <joseph.kogut@gmail.com>,
	 Romain Naour <romain.naour@gmail.com>,
	 Daniel Lang <dalang@gmx.at>,
	 Valentin Korenblit <valentinkorenblit@gmail.com>
Subject: Re: [Buildroot] [RFC PATCH 3/3] package/llvm-project: reduce the build size of llvm
Date: Fri, 04 Jul 2025 12:37:34 +0100	[thread overview]
Message-ID: <87v7o89og1.fsf@draig.linaro.org> (raw)
In-Reply-To: <204c6146-2b48-43d0-94d4-78f030da1f28@smile.fr> (Romain Naour's message of "Thu, 3 Jul 2025 13:16:18 +0200")

Romain Naour <romain.naour@smile.fr> writes:

> Le 03/07/2025 à 13:09, Romain Naour a écrit :
>> Le 03/07/2025 à 08:44, Alex Bennée a écrit :
>>> Romain Naour <romain.naour@smile.fr> writes:
>>>
>>>> Hello Alex, All,
>>>>
>>>> Le 26/06/2025 à 13:16, Alex Bennée a écrit :
>>>>> Although we request a Release build the default CMAKE flags in
>>>>> toolchain.cmake include -Og -g3 which enables debug symbols for the
>>>>> build inflating the overall size of things.
>>>>
>>>> By default, -O2 -g0 is used by Buildroot. If you have -Og -g3 in toolchain.cmake
>>>> generated by Buildroot, it means that BR2_ENABLE_DEBUG, BR2_DEBUG_3 and
>>>> BR2_OPTIMIZE_G have been selected in the Buildroot configuration (by
>>>> the user).
>>>
>>> Where is the logic that sets this? Because:
>>>
>>>   ➜  ag DEBUG .config
>>>   179:BR2_TOOLCHAIN_HAS_THREADS_DEBUG=y
>>>   306:# BR2_ENABLE_DEBUG is not set
>>>   307:# BR2_ENABLE_RUNTIME_DEBUG is not set
>>>   4146:# BR2_PACKAGE_OPENPOWERLINK_DEBUG_LEVEL is not set
>>>
>>> But:
>>>
>>>   ➜  ag "Buildroot CFLAGS" ./host/share/buildroot/toolchainfile.cmake
>>>   57:  set(CMAKE_C_FLAGS "-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Og -g3 -D_FORTIFY_SOURCE=1" CACHE STRING "Buildroot CFLAGS")
>> 
>> It's weird indeed. I had to use BR2_ENABLE_DEBUG, BR2_DEBUG_3 and BR2_OPTIMIZE_G
>> to get the same optimization level than you. Otherwise -O2 -g0 is used.
>> 
>> Can you share a Buildroot defconfig able to reproduce this issue?
>
> Note:
> ./host/share/buildroot/toolchainfile.cmake is generated by the toolchain package
> as post install staging hook:
>
> see:
> TOOLCHAIN_POST_INSTALL_STAGING_HOOKS += TOOLCHAIN_CMAKE_INSTALL_FILES
>
> If the toolchainfile.cmake file was generated with BR2_ENABLE_DEBUG, BR2_DEBUG_3
> and BR2_OPTIMIZE_G set but this setting was updated after, it means you have to
> do a new build. Buildroot doesn't detect such change and a new build from
> scratch is needed.

Ahh that was indeed it. I can drop these patches. Sorry for the noise.

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro
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