Re: [PATCH v2] meson: Allow BPF code to be built with GCC

[Sean Young <sean@mess.org>]

On Sun, Aug 10, 2025 at 03:20:06PM +0100, James Le Cuirot wrote:
> GCC can also target BPF, but it does not understand the "-target bpf"
> arguments passed to Clang.
> 
> Detect it as either bpf-gcc, bpf-none-gcc, or bpf-unknown-none-gcc, the
> same as systemd does.
> 
> Determine the include paths with the compiler used by the rest of the
> build rather than Clang, which might not be installed or might not give
> the right answer, especially when cross-compiling.
> 
> Check whether Clang actually supports the BPF target so that
> auto-detection doesn't cause the build to fail when it doesn't.
> 
> Signed-off-by: James Le Cuirot <chewi@gentoo.org>

Applied. Thank you very much!

Sean

> ---
>  meson.build                                   | 25 ++++++++++++++++++-
>  .../keytable/bpf_protocols/cc_sys_includes.sh | 10 ++++++++
>  .../bpf_protocols/clang_sys_includes.sh       |  9 -------
>  utils/keytable/bpf_protocols/meson.build      | 12 ++++-----
>  utils/keytable/meson.build                    |  2 +-
>  5 files changed, 41 insertions(+), 17 deletions(-)
>  create mode 100755 utils/keytable/bpf_protocols/cc_sys_includes.sh
>  delete mode 100755 utils/keytable/bpf_protocols/clang_sys_includes.sh
> 
> This revision adds the -ftree-switch-conversion flag for GCC, which
> reportedly fixes the "invalid mem access" error. I couldn't figure out
> how to test without any hardware, so I wasn't able to reproduce the
> issue myself, but I trust that it works now.
> 
> diff --git a/meson.build b/meson.build
> index 88781e59..62d271b4 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -83,11 +83,34 @@ endif
>  v4l2_utils_incdir = include_directories(v4l2_utils_incdir_arr)
> 
>  prog_bash = find_program('bash')
> -prog_clang = find_program('clang', required : get_option('bpf'))
>  prog_doxygen = find_program('doxygen', required : get_option('doxygen-doc'))
>  prog_grep = find_program('grep')
>  prog_perl = find_program('perl')
> 
> +if get_option('bpf').allowed()
> +    bpf_args = []
> +    prog_bpf = find_program('bpf-gcc',
> +                            'bpf-none-gcc',
> +                            'bpf-unknown-none-gcc',
> +                            required : false)
> +
> +    if prog_bpf.found()
> +        bpf_args += ['-fno-tree-switch-conversion']
> +    else
> +        prog_bpf = find_program('clang', required : get_option('bpf'))
> +        if prog_bpf.found()
> +            target_bpf = run_command(prog_bpf, '-target', 'bpf', '--print-supported-cpus', check : get_option('bpf').enabled())
> +            if target_bpf.returncode() == 0
> +                bpf_args += ['-target', 'bpf']
> +            else
> +                prog_bpf = disabler()
> +            endif
> +        endif
> +    endif
> +else
> +    prog_bpf = disabler()
> +endif
> +
>  dep_alsa = dependency('alsa', required : false)
>  if dep_alsa.found()
>      conf.set('HAVE_ALSA', 1)
> diff --git a/utils/keytable/bpf_protocols/cc_sys_includes.sh b/utils/keytable/bpf_protocols/cc_sys_includes.sh
> new file mode 100755
> index 00000000..0a8fa277
> --- /dev/null
> +++ b/utils/keytable/bpf_protocols/cc_sys_includes.sh
> @@ -0,0 +1,10 @@
> +#!/bin/sh
> +# Get C compiler's default includes on this system, as the BPF toolchain
> +# generally doesn't see the Linux headers. This fixes "missing" files on some
> +# architectures/distros, such as asm/byteorder.h, asm/socket.h, asm/sockios.h,
> +# sys/cdefs.h etc.
> +#
> +# Use '-idirafter': Don't interfere with include mechanics except where the
> +# build would have failed anyways.
> +"$@" -v -E - </dev/null 2>&1 \
> +	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }'
> diff --git a/utils/keytable/bpf_protocols/clang_sys_includes.sh b/utils/keytable/bpf_protocols/clang_sys_includes.sh
> deleted file mode 100755
> index 9dc4af12..00000000
> --- a/utils/keytable/bpf_protocols/clang_sys_includes.sh
> +++ /dev/null
> @@ -1,9 +0,0 @@
> -#!/bin/sh
> -# Get Clang's default includes on this system, as opposed to those seen by
> -# '-target bpf'. This fixes "missing" files on some architectures/distros,
> -# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
> -#
> -# Use '-idirafter': Don't interfere with include mechanics except where the
> -# build would have failed anyways.
> -$CLANG -v -E - </dev/null 2>&1 \
> -	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }'
> diff --git a/utils/keytable/bpf_protocols/meson.build b/utils/keytable/bpf_protocols/meson.build
> index 1e4f0064..dbb926c4 100644
> --- a/utils/keytable/bpf_protocols/meson.build
> +++ b/utils/keytable/bpf_protocols/meson.build
> @@ -10,9 +10,9 @@ bpf_protocols_files = [
>      'xbox-dvd',
>  ]
> 
> -clang_sys_includes = run_command('clang_sys_includes.sh',
> -                                 check : true,
> -                                 env : ['CLANG=' + prog_clang.full_path()])
> +bpf_args += run_command('cc_sys_includes.sh',
> +                        cc.cmd_array(),
> +                        check : true).stdout().split()
> 
>  foreach file : bpf_protocols_files
>      output = file + '.o'
> @@ -21,9 +21,9 @@ foreach file : bpf_protocols_files
>                    output : output,
>                    input : input,
>                    command : [
> -                      prog_clang,
> -                      clang_sys_includes.stdout().split(),
> -                      '-D__linux__', '-fno-stack-protector', '-target', 'bpf',
> +                      prog_bpf,
> +                      bpf_args,
> +                      '-D__linux__', '-fno-stack-protector',
>                        '-O2', '-c', '@INPUT@', '-o', '@OUTPUT@',
>                    ],
>                    install : true,
> diff --git a/utils/keytable/meson.build b/utils/keytable/meson.build
> index e214e0b5..56e61a79 100644
> --- a/utils/keytable/meson.build
> +++ b/utils/keytable/meson.build
> @@ -22,7 +22,7 @@ ir_keytable_c_args = [
>      '-DIR_KEYTABLE_USER_DIR="@0@"'.format(ir_keytable_user_dir),
>  ]
> 
> -ir_bpf_enabled = prog_clang.found() and dep_libbpf.found() and dep_libelf.found()
> +ir_bpf_enabled = prog_bpf.found() and dep_libbpf.found() and dep_libelf.found()
> 
>  if ir_bpf_enabled
>      ir_keytable_sources += files(
> --
> 2.50.1