[PATCH v3 bpf-next 3/4] bpf: Add cond_break macro

[Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>]

From: Alexei Starovoitov <ast@xxxxxxxxxx>

Use may_goto instruction to implement cond_break macro.
Ideally the macro should be written as:
  asm volatile goto(".byte 0xe5;
                     .byte 0;
                     .short (%l[l_break] - . - 4) / 8;
                     .long 0;
but LLVM doesn't recognize fixup of 2 byte PC relative yet.
Hence use
  asm volatile goto(".byte 0xe5;
                     .byte 0;
                     .long (%l[l_break] - . - 4) / 8;
                     .short 0;
that produces correct asm on little endian.

Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/bpf_experimental.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 0d749006d107..2d408d8b9b70 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -326,6 +326,18 @@ l_true:												\
        })
 #endif
 
+#define cond_break					\
+	({ __label__ l_break, l_continue;		\
+	 asm volatile goto(".byte 0xe5;			\
+		      .byte 0;				\
+		      .long (%l[l_break] - . - 4) / 8;	\
+		      .short 0"				\
+		      :::: l_break);			\
+	goto l_continue;				\
+	l_break: break;					\
+	l_continue:;					\
+	})
+
 #ifndef bpf_nop_mov
 #define bpf_nop_mov(var) \
 	asm volatile("%[reg]=%[reg]"::[reg]"r"((short)var))
-- 
2.34.1