How to use meson with an Android toolchain?

[criatura2]

Hi, I am trying to build dav1d for Android and I am running in the following error

$ meson setup --prefix=...  --libdir=...  --default-library=static --cross-file meson-cross-file.txt path
The Meson build system
Version: 1.6.0
Source dir: ...
Build dir: ...
Build type: cross build
Project name: dav1d
Project version: 0.9.0
C compiler for the host machine: /opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/bin/clang (clang 17.0.2 "Android (11349228, +pgo, +bolt, +lto, -mlgo, based on r487747e) clang version 17.0.2 (https://android.googlesource.com/toolchain/llvm-project d9f89f4d16663d5012e5c09495f3b30ece3d2362)")
C linker for the host machine: /opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/bin/clang ld.lld 17.0.2
Compiler for language c for the build machine not found.
Build machine cpu family: x86_64
Build machine cpu: x86_64
Host machine cpu family: aarch64
Host machine cpu: aarch64
Target machine cpu family: aarch64
Target machine cpu: aarch64
Run-time dependency threads found: YES
Checking for function "clock_gettime" : NO
Library rt found: NO
Checking for function "clock_gettime" with dependency -lrt: NO (cached)

../../dav1d-src/meson.build:142:12: ERROR: Problem encountered: clock_gettime not found

A full log can be found at path/meson-log.txt

The meson-log.txt file contains further information

Using cached compile:
Cached command line:  /opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/bin/clang .../_deps/dav1d-build/Debug/meson-private/tmpaacak3kg/testfile.c -o .../_deps/dav1d-build/Debug/meson-private/tmpaacak3kg/output.exe --sysroot=/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot -D_FILE_OFFSET_BITS=64 -O0 -Werror=implicit-function-declaration -std=c99 -D_GNU_SOURCE 

Code:
 #include <time.h>
        int main(void) {

        /* With some toolchains (MSYS2/mingw for example) the compiler
         * provides various builtins which are not really implemented and
         * fall back to the stdlib where they aren't provided and fail at
         * build/link time. In case the user provides a header, including
         * the header didn't lead to the function being defined, and the
         * function we are checking isn't a builtin itself we assume the
         * builtin is not functional and we just error out. */
        #if !0 && !defined(clock_gettime) && !0
            #error "No definition for __builtin_clock_gettime found in the prefix"
        #endif

        #ifdef __has_builtin
            #if !__has_builtin(__builtin_clock_gettime)
                #error "__builtin_clock_gettime not found"
            #endif
        #elif ! defined(clock_gettime)
            __builtin_clock_gettime;
        #endif
        return 0;
        }
Cached compiler stdout:
 
Cached compiler stderr:
 In file included from .../_deps/dav1d-build/Debug/meson-private/tmpaacak3kg/testfile.c:1:
In file included from /opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/time.h:37:
In file included from /opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/sys/time.h:33:
In file included from /opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/sys/types.h:36:
/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/linux/types.h:21:10: fatal error: 'asm/types.h' file not found
#include <asm/types.h>
         ^~~~~~~~~~~~~
1 error generated.

The meson config file looks like this

[binaries]
c = '/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/bin/clang'
cpp = '/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++'
ar = '/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/bin/llvm-ar'

[host_machine]
cpu_family = 'aarch64'
cpu = 'aarch64'
system = 'linux'
endian = 'little'

[built-in options]
c_args = [ '--sysroot=/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot' ]
c_link_args = [ '--sysroot=/opt/android/ndk/26.2.11394342/toolchains/llvm/prebuilt/linux-x86_64/sysroot' ]

Apparently, meson shouldn't be trying to link with -lrt on Android: https://code.videolan.org/videolan/dav1d/-/merge_requests/854.

Any idea about how to fix this? Thanks.

[sfan5]

here's an example crossfile for Android cross-compilation:

[binaries]
c = 'aarch64-linux-android21-clang'
cpp = 'aarch64-linux-android21-clang++'
ar = 'llvm-ar'
nm = 'llvm-nm'
strip = 'llvm-strip'
pkgconfig = 'pkg-config'
pkg-config = 'pkg-config'
[host_machine]
system = 'android'
cpu_family = 'aarch64'
cpu = 'aarch64'
endian = 'little'

You will need to add the .../toolchains/llvm/prebuilt/linux-x86_64/bin folder to your PATH.