03:51 <derek0883> HI I have probe at libc fread, print($$parms) give me; p=0x7fffffffdd90 mode=0x555555a3e0c0, the definition of FILE *fopen(const char *pathname, const char *mode);

03:52 <derek0883> how can I get the pathname as string, user_string($p) give me something like UUU or VUA

05:23 <derek0883> WARNING: never-assigned local variable 'retval': identifier 'retval'

05:23 <derek0883> probe process("/lib/x86_64-linux-gnu/libc.so.6").function("fopen*").return { printf("%s ret: %d\n", ppfunc(), retval);}

05:24 <derek0883> Why I always got 0, in this retval, and systemtap throw a warning retval never assigned

10:51 <fche> isinstr()

17:25 <derek0883> Hello, I use systemtap to trace fopen of libc, I found static linked version works, but shared library doesn't, the asm code like this: jmpq 0x555555581fe0 <fopen@plt>

17:25 <derek0883> for those call, my system tap didn't catch it.

17:28 <fche> derek0883,

17:28 <fche> how are you probing it?

17:31 <derek0883> probe process("/lib/x86_64-linux-gnu/libc.so.6").function("_IO_new_fopen") { printf("%s file %s\n", ppfunc(), user_string($filename)); }

17:38 <fche> hm, it's roughly working for me here

17:38 <fche> # stap -e 'probe process("/lib64/libc.so.6").function("*fopen") { printf("%s file %s\n", ppfunc(), @defined($filename)?user_string($filename):""); }' -x 3989624

17:38 <derek0883> I use gdb without "systemtap" running, for those file that systemtap can catch, "b fopen", I found the asm code is something like this: 0x7ffff55c886a <__tzfile_read+282> callq 0x7ffff5572e30 <_IO_new_fopen>

17:38 <fche> where that last number is pid of a normal shell

17:39 <fche> there is an _IO_new_fopen and a _IO_new_file_fopen pair on my f31 version of glibc

17:41 <derek0883> same here it is _IO_new_fopen, on ubuntu 18.04

17:48 <derek0883> fche, same here on my ubuntu 18.04, it is can only catch some of fopen,

17:49 <derek0883> I mean same here, the name is _IO_new_fopen and _IO_new_file_fopen

17:50 <fche> and are you sure your workload process is calling this function?

17:50 <fche> stap -v -p2 can tell you e.g. where stap finds the probe points in terms of virtual addresses

17:51 <fche> so can match up the gdb breakpoint address

17:51 <fche> wouldn't expect a bug there.... weird.

17:52 <fche> you could doing a broader wildcard probe of glibc functions function("*").call and watch for the part triggered by your workload's fopen (?) call

17:55 <derek0883> Yes, I'm sure, event use systemtap, if I changed to sys_open, I can catch that file

17:55 <derek0883> Let me try your hint, thanks!

18:04 <fche> hm that's the syscall level

18:04 <fche> eventually it comes through there, yeah

18:48 <derek0883> fche systemtap will also catch each child process, right?

18:48 <fche> yes

19:00 <derek0883> HI fche, after my program called daemon; ( standard c function int daemon(int nochdir, int noclose);) systemtap couldn't catch fopen anymore

19:01 <derek0883> if I comment out daemon(1, 0), then systemtap able to catch all fopen call

19:02 <fche> not sure why that would be

19:02 <fche> the syscall level should work regardless

19:17 <derek0883> Not sure why, But I can repeat reproduce this with a simple Helloword program,

19:18 <derek0883> on my ubuntu 18.04, Systemtap translator/driver (version 4.3/0.170, commit release-4.2-65-g6de9136a2794 + changes)

19:27 <derek0883> fche are you curious to take a quick look? I can upload my simple helloworld program to somewhere?

19:28 <fche> how are you invoking your stap script?

19:29 <derek0883> I'll upload my script and my simple program with a readme

19:30 <fche> are you running stap -x PID or stap -c CMD or stap (with no constraint) ?

19:31 <derek0883> I put it in a .stp file with this on top, #!/usr/local/bin/stap -vg, then I run in bash sudo ./daemon.stp

19:31 <fche> ok

19:31 <derek0883> probe process("/lib/x86_64-linux-gnu/libc.so.6").function("*fopen") { printf("%s %s file %s\n", execname(), ppfunc(), @defined($filename)?user_string($filename):"");}

19:31 <fche> so not constrained to a particular process.

19:32 <fche> daemon() fork/exec's , that's why I asked

19:32 <derek0883> the content of my script is like this

19:45 <derek0883> https://drive.google.com/open?id=1IBu8cI9lNCWO8W08w7hmN1pnNnXEKtDh

19:46 <derek0883> fche Could you please try this link?

19:46 <fche> derek0883, it'll need to wait, sorry, heads down in another piece of work

19:48 <derek0883> No problem, Thanks!