bpf: fix cross build failure on Debian

For compiling bpf code, the system include directory needs to be
constructed. On Debian-like systems, this requires passing a multiarch
directory. Since clang's -dump-machine prints something other that the
multiarch triplet, gcc was interrogated earlier, but that also yields a
wrong result for cross compilation and was thus skipped resulting in
clang not finding asm/types.h.

Rather than, -dump-machine we should ask for -print-multiarch (which
rarely differs). Whenever gcc is in use, this is right (even for cross
building). Since clang does not support -print-multiarch and its
-dump-machine never matches Debian's multiarch, we resort to asking gcc
when building natively. For cross builds using clang, we are out of
luck.

diff --git a/meson.build b/meson.build
index 6d96996acbd9e2f44d2c9a344a91eb06191ba347..724c48adc81f0371f1e524ab559fcbf649c02c48 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -1823,15 +1823,22 @@ if conf.get('BPF_FRAMEWORK') == 1
 
         bpf_o_unstripped_cmd += ['-I.']
 
-        if not meson.is_cross_build()
-                target_triplet_cmd = run_command('gcc', '-dumpmachine', check: false)
-                if target_triplet_cmd.returncode() == 0
-                        target_triplet = target_triplet_cmd.stdout().strip()
-                        bpf_o_unstripped_cmd += [
-                                '-isystem',
-                                '/usr/include/@0@'.format(target_triplet)
-                        ]
+        if cc.get_id() == 'gcc' or meson.is_cross_build()
+                if cc.get_id() != 'gcc'
+                        warning('Cross compiler is not gcc. Guessing the target triplet for bpf likely fails.')
                 endif
+                target_triplet_cmd = run_command(cc.cmd_array(), '-print-multiarch', check: false)
+        else
+                # clang does not support -print-multiarch (D133170) and its -dump-machine
+                # does not match multiarch. Query gcc instead.
+                target_triplet_cmd = run_command('gcc', '-print-multiarch', check: false)
+        endif
+        if target_triplet_cmd.returncode() == 0
+                target_triplet = target_triplet_cmd.stdout().strip()
+                bpf_o_unstripped_cmd += [
+                        '-isystem',
+                        '/usr/include/@0@'.format(target_triplet)
+                ]
         endif
 
         bpf_o_unstripped_cmd += [