selftests/bpf: convenience macro for use with 'asm volatile' blocks

A set of macros useful for writing naked BPF functions using inline
assembly. E.g. as follows:

struct map_struct {
	...
} map SEC(".maps");

SEC(...)
__naked int foo_test(void)
{
	asm volatile(
		"r0 = 0;"
		"*(u64*)(r10 - 8) = r0;"
		"r1 = %[map] ll;"
		"r2 = r10;"
		"r2 += -8;"
		"call %[bpf_map_lookup_elem];"
		"r0 = 0;"
		"exit;"
		:
		: __imm(bpf_map_lookup_elem),
		  __imm_addr(map)
		: __clobber_all);
}
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
[ Kartikeya: Add acks, include __clobber_common from Andrii ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230121002241.2113993-9-memxor@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/progs/bpf_misc.h

@@ -7,6 +7,13 @@
 #define __success		__attribute__((btf_decl_tag("comment:test_expect_success")))
 #define __log_level(lvl)	__attribute__((btf_decl_tag("comment:test_log_level="#lvl)))
 
+/* Convenience macro for use with 'asm volatile' blocks */
+#define __naked __attribute__((naked))
+#define __clobber_all "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "memory"
+#define __clobber_common "r0", "r1", "r2", "r3", "r4", "r5", "memory"
+#define __imm(name) [name]"i"(name)
+#define __imm_addr(name) [name]"i"(&name)
+
 #if defined(__TARGET_ARCH_x86)
 #define SYSCALL_WRAPPER 1
 #define SYS_PREFIX "__x64_"