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From:   James Hilliard <james.hilliard1@gmail.com>
To:     bpf@vger.kernel.org
Cc:     James Hilliard <james.hilliard1@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Subject: [PATCH] libbpf: define bpf_tail_call_static when __clang__ is not defined
Date:   Fri,  9 Sep 2022 16:45:44 -0600
Message-Id: <20220909224544.3702931-1-james.hilliard1@gmail.com>
MIME-Version: 1.0
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The bpf_tail_call_static function is currently not defined unless
using clang >= 8.

To support bpf_tail_call_static on GCC we can check if __clang__ is
not defined to enable bpf_tail_call_static.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 tools/lib/bpf/bpf_helpers.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 7349b16b8e2f..30fc95e7cd76 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -131,7 +131,7 @@
 /*
  * Helper function to perform a tail call with a constant/immediate map slot.
  */
-#if __clang_major__ >= 8 && defined(__bpf__)
+#if (!defined(__clang__) || __clang_major__ >= 8) && defined(__bpf__)
 static __always_inline void
 bpf_tail_call_static(void *ctx, const void *map, const __u32 slot)
 {
@@ -139,8 +139,8 @@ bpf_tail_call_static(void *ctx, const void *map, const __u32 slot)
 		__bpf_unreachable();
 
 	/*
-	 * Provide a hard guarantee that LLVM won't optimize setting r2 (map
-	 * pointer) and r3 (constant map index) from _different paths_ ending
+	 * Provide a hard guarantee that the compiler won't optimize setting r2
+	 * (map pointer) and r3 (constant map index) from _different paths_ ending
 	 * up at the _same_ call insn as otherwise we won't be able to use the
 	 * jmpq/nopl retpoline-free patching by the x86-64 JIT in the kernel
 	 * given they mismatch. See also d2e4c1e6c294 ("bpf: Constant map key
@@ -148,8 +148,8 @@ bpf_tail_call_static(void *ctx, const void *map, const __u32 slot)
 	 *
 	 * Note on clobber list: we need to stay in-line with BPF calling
 	 * convention, so even if we don't end up using r0, r4, r5, we need
-	 * to mark them as clobber so that LLVM doesn't end up using them
-	 * before / after the call.
+	 * to mark them as clobber so that the compiler doesn't end up using
+	 * them before / after the call.
 	 */
 	asm volatile("r1 = %[ctx]\n\t"
 		     "r2 = %[map]\n\t"
-- 
2.34.1