Re: [Qemu-devel] [PATCH] hw/core/loader: do not check for regions overlap

[Peter Maydell]

On 24 July 2017 at 13:21, Hua Yanghao <address@hidden> wrote:
> I think I got where qemu went wrong, it should pick filesz instead of
> memsz, right? ;-)
>
> You see here the filesz does not actually include the bss section
> where if you only check the memsz then it overlaps.
>
>     LOAD off    0x000000e0 vaddr 0x60000000 paddr 0x60000000 align 2**5
>          filesz 0x0007773c memsz 0x00077c00 flags rwx
>
> -----
> PT_LOAD
>
> The array element specifies a loadable segment, described by p_filesz
> and p_memsz. The bytes from the file are mapped to the beginning of
> the memory segment. If the segment's memory size (p_memsz) is larger
> than the file size (p_filesz), the "extra" bytes are defined to hold
> the value 0 and to follow the segment's initialized area. The file
> size may not be larger than the memory size. Loadable segment entries
> in the program header table appear in ascending order,
>
> sorted on the p_vaddr member.
> -----

In the bit of the spec you quote it says how p_memsz > p_filesz
should be handled: "the 'extra' bytes are defined to hold the
value 0". The segment itself is still p_memsz in size and the
header defines that it has zeroes at the end of it. QEMU's loader
needs to arrange that those zeroes are loaded.

thanks
-- PMM