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@xxxxxxxxxxxxx>
---
tools/bpf/bpf_exp.y | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/tools/bpf/bpf_exp.y b/tools/bpf/bpf_exp.y
index 56ba1de50784..8d48e896be50 100644
--- a/tools/bpf/bpf_exp.y
+++ b/tools/bpf/bpf_exp.y
@@ -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);
}
}
}
--
2.23.0
