[Qemu-devel] Help with entry memory area

[João Corrêa]

Hi Guys,

I'm trying to understand better intermediate code generation with qemu and I'm having some problems. I've seen that qemu have some different memory areas, such as code, start_brk, end_code... One of these areas is 'entry'. What exactly this area keeps? I've been able to see, through '-d op' qemu option, that some code is placed in it. I also could notice that it doesn't matter which code I'm running, it will always begin with the below mentioned instructions:

OP:                                                                                                       

 ---- 0x40008025b0                                                                                        

 mov_i64 tmp0,rsp                                                                                         

 mov_i64 rdi,tmp0                                                                                         

                                                                                                          

 ---- 0x40008025b3                                                                                        

 movi_i64 tmp12,$0x40008025b8                                                                             

 movi_i64 tmp13,$0x4000805e40                                                                             

 movi_i64 tmp14,$trace_pc_im                                                                              

 call tmp14,$0x0,$0,tmp13,tmp12

...

After these instruction the program flow follows to a few rdtsc instructions, that are supposedly measuring processor cycles.

Here comes my doubts...

1 - Where exactly in the source code are these instructions that are placed inside entry generated? I've seen that some of them are really translated into IR through the disas_insn(), but how exactly it is done still very unclear to me. If this simulation prologue is always the same, does it really need to be translated into IR?

2 - What exactly the source code placed into the entry memory area is supposed to do? What are the rdtsc instructions used for?

3 - Is there a good place where I can read about how dynamically linked libraries are handled on qemu? If not, where in the source is it handled?

Well, thank you! Any help will be of great use!

Cheers!