selftests/bpf: Introduce cond_break_label

Add a new cond_break_label macro that jumps to the specified label when
the cond_break termination check fires, and allows us to better handle
the uncontrolled termination of the loop.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250306035431.2186189-2-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: kkdwvd

tools/testing/selftests/bpf/bpf_experimental.h

@@ -368,12 +368,12 @@ l_true:												\
 	ret;						\
 	})
 
-#define cond_break					\
+#define __cond_break(expr)				\
 	({ __label__ l_break, l_continue;		\
 	asm volatile goto("may_goto %l[l_break]"	\
 		      :::: l_break);			\
 	goto l_continue;				\
-	l_break: break;					\
+	l_break: expr;					\
 	l_continue:;					\
 	})
 #else
@@ -392,15 +392,15 @@ l_true:												\
 	ret;						\
 	})
 
-#define cond_break					\
+#define __cond_break(expr)				\
 	({ __label__ l_break, l_continue;		\
 	asm volatile goto("1:.byte 0xe5;		\
 		      .byte 0;				\
 		      .long ((%l[l_break] - 1b - 8) / 8) & 0xffff;	\
 		      .short 0"				\
 		      :::: l_break);			\
 	goto l_continue;				\
-	l_break: break;					\
+	l_break: expr;					\
 	l_continue:;					\
 	})
 #else
@@ -418,20 +418,23 @@ l_true:												\
 	ret;						\
 	})
 
-#define cond_break					\
+#define __cond_break(expr)				\
 	({ __label__ l_break, l_continue;		\
 	asm volatile goto("1:.byte 0xe5;		\
 		      .byte 0;				\
 		      .long (((%l[l_break] - 1b - 8) / 8) & 0xffff) << 16;	\
 		      .short 0"				\
 		      :::: l_break);			\
 	goto l_continue;				\
-	l_break: break;					\
+	l_break: expr;					\
 	l_continue:;					\
 	})
 #endif
 #endif
 
+#define cond_break __cond_break(break)
+#define cond_break_label(label) __cond_break(goto label)
+
 #ifndef bpf_nop_mov
 #define bpf_nop_mov(var) \
 	asm volatile("%[reg]=%[reg]"::[reg]"r"((short)var))