How can I find the right source code from the LOG info

[mcygogo]

I just begin to read the source code of VLC, and I found that I can get many informations from the LOG. But I can not find out the right source code which print the info,
for example I get info like this: [0x9df6260] main decoder debug: using decoder module "avcodec" , I just grep the info , but I can get nothing.
How can I find out the c file which print out the info ?
some one can share some experiences about reading the source code?

[Rémi Denis-Courmont]

That's the module_need() function.

[mcygogo]

Ok, tks, I just got it. I redefined the msg_Dbg like this:
#define msg_Dbg( p_this, ... ) \
do{\
msg_Generic( VLC_OBJECT(p_this), VLC_MSG_DBG, \
MODULE_STRING, __VA_ARGS__ ); \
fprintf(stderr, "file:%s func:%s line:%d \n", __FILE__, __func__, __LINE__); \
}while(0)

Then I got everything I want