Commit 06375801 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Andrii Nakryiko
Browse files

bpf: Add cond_break macro 



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] ...
                     .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] ...
                     .short 0;
that produces correct asm on little endian.

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Tested-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20240306031929.42666-4-alexei.starovoitov@gmail.com
parent 4f81c16f

tools/testing/selftests/bpf/bpf_experimental.h

+12 −0
Original line number Diff line number Diff line
@@ -326,6 +326,18 @@ l_true: \ 
       })

#endif



#define cond_break					\

	({ __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_continue:;					\

	})



#ifndef bpf_nop_mov

#define bpf_nop_mov(var) \

	asm volatile("%[reg]=%[reg]"::[reg]"r"((short)var))