Re: [PATCH v3 7/7] perf docs: Remove the Android cross building document

[James Clark <james.clark@linaro.org>]

On 12/07/2024 12:02 pm, Leo Yan wrote:
> Hi Namhyung,
> 
> On 7/12/24 05:58, Namhyung Kim wrote:
>> On Sat, Jul 06, 2024 at 07:29:12PM +0100, Leo Yan wrote:
> 
> [...]
> 
>>> The Android NDK (as time being the latest LTS version is r26d) changes
>>> toolchain to LLVM / Clang, so GCC compilers is not included in the NDK
>>> anymore. Therefore, the Android document contains obsolete info for
>>> building perf binary with NDK.
>>
>> Do you know if the version prior to the change is still used?
> 
> Based on the Android NDK wiki claims [1], since NDK r15 (backed to 26th
> July, 2017) "GCC is no longer supported. It will not be removed from the 
> NDK
> just yet, but is no longer receiving backports".
> 
>>> Furthermore, the Clang included in the Android NDK is problematic for
>>> cross compilation Aarch64 target. The building reports multiple errors
>>> with the compiler aarch64-linux-android34-clang.
>>>
>>> Thus, delete Documentation/android.txt to avoid confusion.
>>
>> If so, maybe we can keep the document little more and add a note that
>> this works only for some old versions.
>>
>> I'm also curious if it's still broken after your fixes.
> 
> When I tried Android NDK for cross building perf, it is still broken after
> applied this series.
> 
>  From my testing, now using LLVM for native building works well:
> 
>    make LLVM=-15 VF=1 DEBUG=1 -C tools/perf
> 
> But it failed for cross compilation. Since Android NDK system root does not
> contain some dependency libs, we must use extra options to disable some
> features (e.g. NO_LIBELF=1 NO_LIBTRACEEVENT=1). The commands I tried for
> cross building but failed:
> 
>    make ARCH=arm64 CC=$NDK_TOOLCHAIN/aarch64-linux-android-clang \
>      LD=$NDK_TOOLCHAIN/ld.lld AR=$NDK_TOOLCHAIN/llvm-ar \
>      NM=$NDK_TOOLCHAIN/llvm-nm STRIP=$NDK_TOOLCHAIN/llvm-strip \
>      OBJCOPY=$NDK_TOOLCHAIN/llvm-objcopy \
>      OBJDUMP=$NDK_TOOLCHAIN/llvm-objdump \
>      READELF=$NDK_TOOLCHAIN/llvm-readelf \
>      HOSTCC=$NDK_TOOLCHAIN/clang \
>      HOSTCXX=$NDK_TOOLCHAIN/clang++ HOSTAR=$NDK_TOOLCHAIN/llvm-ar \
>      HOSTLD=$NDK_TOOLCHAIN/ld.lld VF=1 DEBUG=1 NO_LIBELF=1 \
>      NO_LIBTRACEEVENT=1 EXTRA_CFLAGS=-fgnuc-version=0 \
>      -C tools/perf
> 
> Given the test result, my conclusion is the doc for Android cross building
> is not useful for a long while. If we really want to support it, I would
> like to suggest to take a separate task for fixing LLVM / Clang cross
> compilation.

We could replace the entire contents of the file with something like 
"Android NDK compilation deprecated -- no longer supported". It might 
help someone in being able to recover the history of the file by leaving 
in some keywords. If you delete it it becomes very unlikely that the 
history will be found by someone trying to get it working again.

> 
> Thanks,
> Leo
> 
> [1] https://github.com/android/ndk/wiki/Changelog-r15