Pardon me for any possibly stupid answer...so here we come :) On Mon, Jan 24, 2011 at 18:34, Stefano Bonifazi <stefboombas...@gmail.com> wrote: > First of all: >> >> info->start_mmap = (abi_ulong)ELF_START_MMAP; > > What is this?
Start address in which address the ELF code section, in reality (not under qemu-user) should be mapped. in x86 32 bit it's 08048000, you can check it by yourself by executing: cat /proc/self/maps however, as you already know, it might be relocated elsewhere if the code is PIC or PIE (Position Independent Executable). I wrote an article about understanding ELF years ago, here is the URL: http://www.linuxforums.org/articles/understanding-elf-using-readelf-and-objdump_125.html >what is start_mmap supposed to point at at the end? Why that > static value is chosen at the beginning? in qemu 0.13.0, linux-user/elfload.c, lines around 1728 to 1761, you will find that start_mmap is kinda an address that is the result of mmap operation that will be filled with the code in code section. It will be a "hint" on which address the guest code really points when dealing with memory address. I dare to guess that, every code executed in the guest...when referring to virtual address, will be get substracted by the delta of ELF_START_MMAP and real_base. It's like "hey, it's written A in the code, but it's mapped in B, ok so the delta is A-B, call it X. Then every address in the code should be substracted (or added, depending on how you see it) with X, then it will point in qemu mmaped VMA" See the codes, read it slowly, you wil get the idea. I am claiming I know it 100%, but I think that's the way it is PS: IMHO the real guru is still the one and only Fabrice Bellard, too bad he's out of qemu. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com
