diff options
| author | Ilya Leoshkevich | 2019-11-07 11:03:49 +0100 |
|---|---|---|
| committer | Daniel Borkmann | 2019-11-07 16:01:34 +0100 |
| commit | 7e22077d0c73a68ff3fd8b3d2f6564fcbcf8cb23 (patch) | |
| tree | 341749de11e136cd25048774bc1ccbc765172fbf /tools/bpf | |
| parent | 85d31dd07002315c0d1816543fdc392c8cc6b73a (diff) | |
tools, bpf_asm: Warn when jumps are out of range
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
Diffstat (limited to 'tools/bpf')
| -rw-r--r-- | tools/bpf/bpf_exp.y | 14 |
1 files 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); } } } |