fix a trace.py problem (#1973)
Currently, trace.py failed for the following command:
$ sudo ./trace.py 'filename_lookup(int dfd, struct filename *name) "%s", name->name'
...
0: (bf) r6 = r1
1: (79) r7 = *(u64 *)(r6 +104)
...
32: (15) if r1 == 0x0 goto pc+5
R0=inv(id=0) R1=inv(id=0) R6=ctx(id=0,off=0,imm=0) R7=inv(id=0)
R8=inv0 R10=fp0,call_-1 fp-8=0 fp-16=0 fp-24=0 fp-32=0 fp-40=0 fp-48=0 fp-56=0 fp-64=0 fp-72=0 fp-80=0
33: (79) r3 = *(u64 *)(r7 +0)
R7 invalid mem access 'inv'
For string format argument, the trace.py generates the below code:
if (name->name != 0) {
bpf_probe_read(&__data.v0, sizeof(__data.v0), (void *)name->name);
}
Right now, bcc skips the rewriter for the third argument of bpf_probe_read to avoid
unnecessary nested bpf_probe_read and other potential issues.
This causes name->name memory access not transformed with bpf_probe_read and hence
the verifier complains.
To fix the issue, this patch did the following transformation using an
temporary variable to hold the src address:
if (name->name != 0) {
void *__tmp = (void *)name->name;
bpf_probe_read(&__data.v0, sizeof(__data.v0), __tmp);
}
This way, rewriter can do the work properly.
Signed-off-by: Yonghong Song <yhs@fb.com>diff --git a/tools/trace.py b/tools/trace.py
index 051ba9b..d21bc0e 100755
--- a/tools/trace.py
+++ b/tools/trace.py
@@ -390,9 +390,10 @@
if field_type == "s":
return text + """
if (%s != 0) {
- bpf_probe_read(&__data.v%d, sizeof(__data.v%d), (void *)%s);
+ void *__tmp = (void *)%s;
+ bpf_probe_read(&__data.v%d, sizeof(__data.v%d), __tmp);
}
- """ % (expr, idx, idx, expr)
+ """ % (expr, expr, idx, idx)
if field_type in Probe.fmt_types:
return text + " __data.v%d = (%s)%s;\n" % \
(idx, Probe.c_type[field_type], expr)