Issues:
1. bpf_probe_read is no longer available for architecture which has
overlapping address space. Hence bpf prologue generation fails
2. perf probe -a 'do_sched_setscheduler pid policy
param->sched_priority@user' did not work before.
Fixes:
1. Use bpf_probe_read_kernel for kernel member access. For user
attribute access in kprobes, bpf_probe_read_user is utilized
2. Make (perf probe -a 'do_sched_setscheduler pid policy
param->sched_priority@user') output equivalent to ftrace
('p:probe/do_sched_setscheduler _text+517384 pid=%r2:s32
policy=%r3:s32 sched_priority=+u0 (%r4):s32' > kprobe_events)
Other:
1. Right now, __match_glob() does not handle [u]<offset>. For now, use
*u]<offset>.
2. @user attribute was introduced in commit 1e032f7cfa14 ("perf-probe:
Add user memory access attribute support")
Test:
1. ulimit -l 128 ; ./perf record -e tests/bpf_sched_setscheduler.c
2. cat tests/bpf_sched_setscheduler.c
static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) =
(void *) 6;
static int (*bpf_probe_read_user)(void *dst, __u32 size,
const void *unsafe_ptr) = (void *) 112;
static int (*bpf_probe_read_kernel)(void *dst, __u32 size,
const void *unsafe_ptr) = (void *) 113;
SEC("func=do_sched_setscheduler pid policy param->sched_priority@user")
int bpf_func__setscheduler(void *ctx, int err, pid_t pid, int policy,
int param)
{
char fmt[] = "prio: %ld";
bpf_trace_printk(fmt, sizeof(fmt), param);
return 1;
}
char _license[] SEC("license") = "GPL";
int _version SEC("version") = LINUX_VERSION_CODE;
3. ./perf script
sched 305669 [000] 1614458.838675: perf_bpf_probe:func: (2904e508)
pid=261614 policy=2 sched_priority=1
4. cat /sys/kernel/debug/tracing/trace
<...>-309956 [006] .... 1616098.093957: 0: prio: 1
5. bpf_probe_read_user is used when @user attribute is used. Otherwise,
defaults to bpf_probe_read_kernel
6. ./perf test bpf (null_lseek - kernel member access)
42: BPF filter :
42.1: Basic BPF filtering : Ok
42.2: BPF pinning : Ok
42.3: BPF prologue generation : Ok
42.4: BPF relocation checker : FAILED!
Signed-off-by: Sumanth Korikkar <sumanthk@xxxxxxxxxxxxx>
Reviewed-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
---
tools/perf/util/bpf-prologue.c | 14 ++++++++++----
tools/perf/util/probe-event.c | 7 +++++--
tools/perf/util/probe-file.c | 2 +-
3 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/bpf-prologue.c b/tools/perf/util/bpf-prologue.c
index b020a8678eb9..9887ae09242d 100644
--- a/tools/perf/util/bpf-prologue.c
+++ b/tools/perf/util/bpf-prologue.c
@@ -142,7 +142,8 @@ static int
gen_read_mem(struct bpf_insn_pos *pos,
int src_base_addr_reg,
int dst_addr_reg,
- long offset)
+ long offset,
+ int probeid)
{
/* mov arg3, src_base_addr_reg */
if (src_base_addr_reg != BPF_REG_ARG3)
@@ -159,7 +160,7 @@ gen_read_mem(struct bpf_insn_pos *pos,
ins(BPF_MOV64_REG(BPF_REG_ARG1, dst_addr_reg), pos);
/* Call probe_read */
- ins(BPF_EMIT_CALL(BPF_FUNC_probe_read), pos);
+ ins(BPF_EMIT_CALL(probeid), pos);
/*
* Error processing: if read fail, goto error code,
* will be relocated. Target should be the start of
@@ -241,7 +242,7 @@ static int
gen_prologue_slowpath(struct bpf_insn_pos *pos,
struct probe_trace_arg *args, int nargs)
{
- int err, i;
+ int err, i, probeid;
for (i = 0; i < nargs; i++) {
struct probe_trace_arg *arg = &args[i];
@@ -276,11 +277,16 @@ gen_prologue_slowpath(struct bpf_insn_pos *pos,
stack_offset), pos);
ref = arg->ref;
+ probeid = BPF_FUNC_probe_read_kernel;
while (ref) {
pr_debug("prologue: arg %d: offset %ld\n",
i, ref->offset);
+
+ if (ref->user_access)
+ probeid = BPF_FUNC_probe_read_user;
+
err = gen_read_mem(pos, BPF_REG_3, BPF_REG_7,
- ref->offset);
+ ref->offset, probeid);
if (err) {
pr_err("prologue: failed to generate probe_read function call\n");
goto errout;
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index eea132f512b0..7cdb66ef3baa 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1565,7 +1565,7 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
}
tmp = strchr(str, '@');
- if (tmp && tmp != str && strcmp(tmp + 1, "user")) { /* user attr */
+ if (tmp && tmp != str && !strcmp(tmp + 1, "user")) { /* user attr */
if (!user_access_is_supported()) {
semantic_error("ftrace does not support user access\n");
return -EINVAL;
@@ -1986,7 +1986,10 @@ static int __synthesize_probe_trace_arg_ref(struct probe_trace_arg_ref *ref,
if (depth < 0)
return depth;
}
- err = strbuf_addf(buf, "%+ld(", ref->offset);
+ if (ref->user_access)
+ err = strbuf_addf(buf, "%s%ld(", "+u", ref->offset);
+ else
+ err = strbuf_addf(buf, "%+ld(", ref->offset);
return (err < 0) ? err : depth;
}
diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
index 8c852948513e..064b63a6a3f3 100644
--- a/tools/perf/util/probe-file.c
+++ b/tools/perf/util/probe-file.c
@@ -1044,7 +1044,7 @@ static struct {
DEFINE_TYPE(FTRACE_README_PROBE_TYPE_X, "*type: * x8/16/32/64,*"),
DEFINE_TYPE(FTRACE_README_KRETPROBE_OFFSET, "*place (kretprobe): *"),
DEFINE_TYPE(FTRACE_README_UPROBE_REF_CTR, "*ref_ctr_offset*"),
- DEFINE_TYPE(FTRACE_README_USER_ACCESS, "*[u]<offset>*"),
+ DEFINE_TYPE(FTRACE_README_USER_ACCESS, "*u]<offset>*"),
DEFINE_TYPE(FTRACE_README_MULTIPROBE_EVENT, "*Create/append/*"),
DEFINE_TYPE(FTRACE_README_IMMEDIATE_VALUE, "*\\imm-value,*"),
};
--
2.25.4
