bpf: Abstract loop unrolling pragmas in BPF selftests

[Changes from V1:
- Avoid conflict by rebasing with latest master.]

Some BPF tests use loop unrolling compiler pragmas that are clang
specific and not supported by GCC.  These pragmas, along with their
GCC equivalences are:

  #pragma clang loop unroll_count(N)
  #pragma GCC unroll N

  #pragma clang loop unroll(full)
  #pragma GCC unroll 65534

  #pragma clang loop unroll(disable)
  #pragma GCC unroll 1

  #pragma unroll [aka #pragma clang loop unroll(enable)]
  There is no GCC equivalence to this pragma.  It enables unrolling on
  loops that the compiler would not ordinarily unroll even with
  -O2|-funroll-loops, but it is not equivalent to full unrolling
  either.

This patch adds a new header progs/bpf_compiler.h that defines the
following macros, which correspond to each pair of compiler-specific
pragmas above:

  __pragma_loop_unroll_count(N)
  __pragma_loop_unroll_full
  __pragma_loop_no_unroll
  __pragma_loop_unroll

The selftests using loop unrolling pragmas are then changed to include
the header and use these macros in place of the explicit pragmas.

Tested in bpf-next master.
No regressions.

Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240208203612.29611-1-jose.marchesi@oracle.com

1 files changed, 33 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/bpf_compiler.h b/tools/testing/selftests/bpf/progs/bpf_compiler.h
new file mode 100644
index 000000000000..a7c343dc82e6
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_compiler.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __BPF_COMPILER_H__
+#define __BPF_COMPILER_H__
+
+#define DO_PRAGMA_(X) _Pragma(#X)
+
+#if __clang__
+#define __pragma_loop_unroll DO_PRAGMA_(clang loop unroll(enable))
+#else
+/* In GCC -funroll-loops, which is enabled with -O2, should have the
+   same impact than the loop-unroll-enable pragma above.  */
+#define __pragma_loop_unroll
+#endif
+
+#if __clang__
+#define __pragma_loop_unroll_count(N) DO_PRAGMA_(clang loop unroll_count(N))
+#else
+#define __pragma_loop_unroll_count(N) DO_PRAGMA_(GCC unroll N)
+#endif
+
+#if __clang__
+#define __pragma_loop_unroll_full DO_PRAGMA_(clang loop unroll(full))
+#else
+#define __pragma_loop_unroll_full DO_PRAGMA_(GCC unroll 65534)
+#endif
+
+#if __clang__
+#define __pragma_loop_no_unroll DO_PRAGMA_(clang loop unroll(disable))
+#else
+#define __pragma_loop_no_unroll DO_PRAGMA_(GCC unroll 1)
+#endif
+
+#endif