No output when running ltrace

问题

As the title says, ltrace does not work properly on my system. It shows no output in most cases, like

$ltrace ls
[usual ls output]
+++ exited (status 0) +++

$gcc hello.c
$ltrace ./a.out
Hello world!
+++ exited (status 0) +++

I'm using the latest ltrace version (from package 0.7.3-5.1ubuntu4), I even tried recompiling from source with no difference. I'm using Ubuntu 16.10, kernel 4.8.0-42-generic. gcc version is 6.2.0.

Weird thing is, binaries downloaded from the Internet seem to work, correctly displaying the library calls.

What am I missing? Is anyone able to reproduce the issue?

回答1:

This may have to do with binaries being compiled with "relro now". I created a quick test program (I'm using Ubuntu 16.04):

int main() {
  write(0, "hello\n", 6);
  return 0;
}

If I compile it with gcc -O2 test.c -o test then ltrace works:

$ ltrace ./test 
__libc_start_main(0x400430, 1, 0x7ffc12326528, 0x400550 <unfinished ...>
write(0, "hello\n", 6hello
)                                                              = 6
+++ exited (status 0) +++

However when I compile with gcc -O2 test.c -Wl,-z,relro -Wl,-z,now -o test2 then it doesn't:

$ ltrace ./test2 
hello
+++ exited (status 0) +++

You can check if a binary was compiled like so using scanelf from the pax-utils package on Ubuntu:

$ scanelf -a test*
 TYPE    PAX   PERM ENDIAN STK/REL/PTL TEXTREL RPATH BIND FILE 
ET_EXEC PeMRxS 0775 LE RW- R-- RW-    -      -   LAZY test 
ET_EXEC PeMRxS 0775 LE RW- R-- RW-    -      -   NOW test2

Note the LAZY (ltrace works) versus NOW (ltrace doesn't).

There is a little bit more discussion (but no resolution) here:

https://bugzilla.redhat.com/show_bug.cgi?id=1333481

来源：https://stackoverflow.com/questions/43213505/no-output-when-running-ltrace

标签

Linux

Ubuntu

shared-libraries

ltrace