将 Valgrind 与 LD_PRELOAD 一起使用

Question

To run a program, I add an LD_PRELOAD variable before the command to load a specific library for instrumentation. So the command looks like

LD_PRELOAD=foo.so ./run_program

In order to use valgrind, If I run valgrind LD_PRELOAD=foo.so./run_program , I get:

valgrind: LD_PRELOAD=foo.so: No such file or directory

And if I run LD_PRELOAD=foo.so valgrind./run_program , the loaded library doesn't come into effect. So, I would like to know how to attach valgrind to the program with the loaded library. Any thoughts on that?

Answer 1

You need to set LD_PRELOAD before both Valgrind and the guest executable.

Valgrind expects the first non-valgrind argument to be the application to be run (either a script or an ELF executable binary).

For example, running the following script

#!/usr/bin/env ksh

print $LD_PRELOAD

$ LD_PRELOAD=/lib64/libc.so.6 valgrind -q./sh
/lib64/libc.so.6

There is no way to "attach" Valgrind to a running executable. It does not use ptrace like debuggers (gdb, lldb and udb for instance).

More details on what is going on are here and the full thread

Finally, if you run valgrind with -v you should see something like this (there is a lot of output so I've trimmed a lot). The example below was run with

valgrind -d pwd
export LD_PRELOAD=./myprint.so

--18766:1: aspacem (0,4,5) /usr/lib64/valgrind/memcheck-amd64-linux
--18766:1: aspacem (1,49,3) /usr/bin/pwd
--18766:1: aspacem (2,66,3) /usr/lib64/ld-2.17.so
[memory map]

memcheck was exec'd by valgrind, and memcheck then mmap'd the guest (pwd) and ld.so, then it started executing the guest, which will start loading dependencies.

--18766:1: aspacem (0,4,5) /usr/lib64/valgrind/memcheck-amd64-linux
--18766:1: aspacem (1,49,4) /usr/bin/pwd
--18766:1: aspacem (2,66,4) /usr/lib64/ld-2.17.so
--18766:1: aspacem (4,162,5) /usr/lib64/valgrind/vgpreload_core-amd64-linux.so
--18766:1: aspacem (5,216,5) /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so
--18766:1: aspacem (6,274,8) /home/paulf/scratch/valgrind/cachegrind/tests/myprint.so
--18766:1: aspacem (7,337,0) [free slot: size=17  next=0]
--18766:1: aspacem (8,358,5) /usr/lib64/libc-2.17.so
[more detailed memory map]

Here the guest has loaded the libs listed in LD_PRELOAD (myprint.so and also core and memcheck, which valgrind added to LD_PRELOAD before execing memcheck).