tools, bpf_asm: Warn when jumps are out of range (7e22077d) · Commits · 戴 / test

When compiling larger programs with bpf_asm, it's possible to accidentally exceed jt/jf range, in which case it won't complain, but rather silently emit a truncated offset, leading to a "happy debugging" situation. Add a warning to help detecting such issues. It could be made an error instead, but this might break compilation of existing code (which might be working by accident). Signed-off-by:

Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20191107100349.88976-1-iii@linux.ibm.com

tools/bpf/bpf_exp.y

+12 −2

Original line number	Diff line number	Diff line
		@@ -545,6 +545,16 @@ static void bpf_reduce_k_jumps(void)
		}
		}

		static uint8_t bpf_encode_jt_jf_offset(int off, int i)
		{
		int delta = off - i - 1;

		if (delta < 0 \|\| delta > 255)
		fprintf(stderr, "warning: insn #%d jumps to insn #%d, "
		"which is out of range\n", i, off);
		return (uint8_t) delta;
		}

		static void bpf_reduce_jt_jumps(void)
		{
		int i;
		@@ -552,7 +562,7 @@ static void bpf_reduce_jt_jumps(void)
		for (i = 0; i < curr_instr; i++) {
		if (labels_jt[i]) {
		int off = bpf_find_insns_offset(labels_jt[i]);
		out[i].jt = (uint8_t) (off - i -1);
		out[i].jt = bpf_encode_jt_jf_offset(off, i);
		}
		}
		}
		@@ -564,7 +574,7 @@ static void bpf_reduce_jf_jumps(void)
		for (i = 0; i < curr_instr; i++) {
		if (labels_jf[i]) {
		int off = bpf_find_insns_offset(labels_jf[i]);
		out[i].jf = (uint8_t) (off - i - 1);
		out[i].jf = bpf_encode_jt_jf_offset(off, i);
		}
		}
		}

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