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bpf: Add cond_break macro

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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: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Tested-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20240306031929.42666-4-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2024-03-05 19:19:28 -08:00 committed by Andrii Nakryiko
parent 4f81c16f50
commit 0637580152
1 changed files with 12 additions and 0 deletions
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12
tools/testing/selftests/bpf/bpf_experimental.h
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@ -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))