sirhao/memcapture

A simple test for get application-level mem alloc by LD_PRELOAD

0.dependebcy

# ubuntu 18+
> apt-get update
> apt-get install -y gcc git make
> git pull https://github.com/SirHao/MemCapture

1.Userspace demo

test1/main.c is a demo of user's application, use

$test1: gcc -o main main.c

to complie. Then, use following command to run this demo:

$test1: ./main
$out> 	a b c d e f g h i
  	a b c d e f g h i
  	a b c d e f g h i

2.Our workspace

test2/ is our main workspace to capture user-application systemcall on malloc(2) and free(1) The Makefile is already done, use

$test2: make

to update the Mem.so for every modification

• note: since printf(...) also use malloc(2) to alloc a buffer, in mem.c, use fprintf(stderr,xxx) intead of printf. Otherwise, core dump occures.

3.Load Mem.so into user application

in the terminal used to run test1/main, before run, type:

export LD_PRELOAD=/home/xx/test2xxx/Mem.so     # notice: use absolute path of Mem.so

this will load Mem.so into this terminal . From now on, all following processes in this terminal will firstly call our func with the same name (now, we only capture to systemcall malloc and ``). Then:

./main

you will find there are something diff. from before, the user application will firstly enter our mem.c:malloc(2), print sth. , then call the real malloc(2) in our logic., the out put is:

[malloc] request:10
[malloc] request:1024
a b c d e f g h i 
[free] free
[malloc] request:10
a b c d e f g h i 
[free] free
[malloc] request:10
a b c d e f g h i 
[free] free