libbpf-tools: Fix syscount

Running syscount causes the following error:

    ...
    ; if (measure_latency)
    103: (18) r1 = 0xffffc90000b6a002
    105: (71) r1 = *(u8 *)(r1 +0)
    R0_w=inv(id=0,umax_value=16,var_off=(0x0; 0x1f)) R1_w=map_value(id=0,off=2,ks=4,vs=48,imm=0) R7=map_value(id=0,off=0,ks=4,vs=32,imm=0) R8=inv(id=0,smin_value=-2147483648,smax_value=2147483647) R10=fp0 fp-8=mmmmmmmm fp-16=mmmmmmmm
    ; if (measure_latency)
    106: (15) if r1 == 0x0 goto pc+4
    R0_w=inv(id=0,umax_value=16,var_off=(0x0; 0x1f)) R1_w=inv(id=0,umax_value=255,var_off=(0x0; 0xff)) R7=map_value(id=0,off=0,ks=4,vs=32,imm=0) R8=inv(id=0,smin_value=-2147483648,smax_value=2147483647) R10=fp0 fp-8=mmmmmmmm fp-16=mmmmmmmm
    ; __sync_fetch_and_add(&val->total_ns, bpf_ktime_get_ns() - *start_ts);
    107: (85) call bpf_ktime_get_ns#5
    ; __sync_fetch_and_add(&val->total_ns, bpf_ktime_get_ns() - *start_ts);
    108: (79) r1 = *(u64 *)(r6 +0)
    R6 !read_ok
    processed 181 insns (limit 1000000) max_states_per_insn 1 total_states 19 peak_states 19 mark_read 8
    -- END PROG LOAD LOG --
    libbpf: failed to load program 'sys_exit'
    libbpf: failed to load object 'syscount_bpf'
    libbpf: failed to load BPF skeleton 'syscount_bpf': -13
    failed to load BPF object: Permission denied

Fix this by calculating the latency and store on a local variable.

Signed-off-by: Hengqi Chen <[email protected]>

Author: chenhengqi

libbpf-tools/syscount.bpf.c

@@ -78,7 +78,7 @@ int sys_exit(struct trace_event_raw_sys_exit *args)
 	static const struct data_t zero;
 	pid_t pid = id >> 32;
 	struct data_t *val;
-	u64 *start_ts;
+	u64 *start_ts, lat = 0;
 	u32 tid = id;
 	u32 key;
 
@@ -97,6 +97,7 @@ int sys_exit(struct trace_event_raw_sys_exit *args)
 		start_ts = bpf_map_lookup_elem(&start, &tid);
 		if (!start_ts)
 			return 0;
+		lat = bpf_ktime_get_ns() - *start_ts;
 	}
 
 	key = (count_by_process) ? pid : args->id;
@@ -106,7 +107,7 @@ int sys_exit(struct trace_event_raw_sys_exit *args)
 		if (count_by_process)
 			save_proc_name(val);
 		if (measure_latency)
-			__sync_fetch_and_add(&val->total_ns, bpf_ktime_get_ns() - *start_ts);
+			__sync_fetch_and_add(&val->total_ns, lat);
 	}
 	return 0;
 }