From acc8800b6f4380b6f4c7f04ee9a1263cf11deb35 Mon Sep 17 00:00:00 2001
From: Jerome Marchand <jmarchan@redhat.com>
Date: Tue, 20 Dec 2022 11:33:51 +0100
Subject: [PATCH] tools: nfsslower: fix an uninitialized struct error

Fixes the following error:
bpf: Failed to load program: Permission denied
reg type unsupported for arg#0 function trace_read_return#22
0: R1=ctx(off=0,imm=0) R10=fp0
; int trace_read_return(struct pt_regs *ctx)
0: (bf) r6 = r1                       ; R1=ctx(off=0,imm=0) R6_w=ctx(off=0,imm=0)

[...]

; bpf_probe_read_kernel(&data.file, sizeof(data.file), (void *)qs.name);
75: (b7) r2 = 32                      ; R2_w=32
76: (85) call bpf_probe_read_kernel#113       ; R0_w=scalar() fp-16=????mmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm fp-48=mmmmmmmm
; bpf_perf_event_output(ctx, (void *)bpf_pseudo_fd(1, -2), CUR_CPU_IDENTIFIER, &data, sizeof(data));
77: (18) r2 = 0xffff9a0a42177200      ; R2_w=map_ptr(off=0,ks=4,vs=4,imm=0)
79: (bf) r4 = r10                     ; R4_w=fp0 R10=fp0
; bpf_probe_read_kernel(&data.file, sizeof(data.file), (void *)qs.name);
80: (07) r4 += -104                   ; R4_w=fp-104
; bpf_perf_event_output(ctx, (void *)bpf_pseudo_fd(1, -2), CUR_CPU_IDENTIFIER, &data, sizeof(data));
81: (bf) r1 = r6                      ; R1_w=ctx(off=0,imm=0) R6=ctx(off=0,imm=0)
82: (18) r3 = 0xffffffff              ; R3_w=4294967295
84: (b7) r5 = 96                      ; R5_w=96
85: (85) call bpf_perf_event_output#25
invalid indirect read from stack R4 off -104+92 size 96
processed 82 insns (limit 1000000) max_states_per_insn 0 total_states 4 peak_states 4 mark_read 3

Traceback (most recent call last):
  File "/usr/share/bcc/tools/nfsslower", line 283, in <module>
    b.attach_kretprobe(event="nfs_file_read", fn_name="trace_read_return")
  File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 872, in attach_kretprobe
    fn = self.load_func(fn_name, BPF.KPROBE)
  File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 523, in load_func
    raise Exception("Failed to load BPF program %s: %s" %
Exception: Failed to load BPF program b'trace_read_return': Permission denied
---
 tools/nfsslower.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/nfsslower.py b/tools/nfsslower.py
index b5df8f19..682a3fb7 100755
--- a/tools/nfsslower.py
+++ b/tools/nfsslower.py
@@ -179,8 +179,12 @@ static int trace_exit(struct pt_regs *ctx, int type)
 
     // populate output struct
     u32 size = PT_REGS_RC(ctx);
-    struct data_t data = {.type = type, .size = size, .delta_us = delta_us,
-        .pid = pid};
+    struct data_t data;
+    __builtin_memset(&data, 0, sizeof(data));
+    data.type = type;
+    data.size = size;
+    data.delta_us = delta_us;
+    data.pid = pid;
     data.ts_us = ts / 1000;
     data.offset = valp->offset;
     bpf_get_current_comm(&data.task, sizeof(data.task));
-- 
2.38.1