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, 3 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_seg6_loop.c b/tools/testing/selftests/bpf/progs/test_seg6_loop.c
index a7278f064368..5059050f74f6 100644
--- a/tools/testing/selftests/bpf/progs/test_seg6_loop.c
+++ b/tools/testing/selftests/bpf/progs/test_seg6_loop.c
@@ -6,6 +6,8 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 
+#include "bpf_compiler.h"
+
 /* Packet parsing state machine helpers. */
 #define cursor_advance(_cursor, _len) \
 	({ void *_tmp = _cursor; _cursor += _len; _tmp; })
@@ -134,7 +136,7 @@ static __always_inline int is_valid_tlv_boundary(struct __sk_buff *skb,
 	// we can only go as far as ~10 TLVs due to the BPF max stack size
 	// workaround: define induction variable "i" as "long" instead
 	// of "int" to prevent alu32 sub-register spilling.
-	#pragma clang loop unroll(disable)
+	__pragma_loop_no_unroll
 	for (long i = 0; i < 100; i++) {
 		struct sr6_tlv_t tlv;