Re: [Qemu-devel] [PATCH 1/2] loader: Handle ELF files with overlapping zero-initialized data

[Richard Henderson]

On 08/07/2017 07:39 AM, Peter Maydell wrote:
> For embedded systems, notably ARM, one common use of ELF
> file segments is that the 'physical addresses' represent load addresses
> and the 'virtual addresses' execution addresses, such that
> the load addresses are packed into ROM or flash, and the
> relocation and zero-initialization of data is done at runtime.
> This means that the 'memsz' in the segment header represents
> the runtime size of the segment, but the size that needs to
> be loaded is only the 'filesz'. In particular, paddr+memsz
> may overlap with the next segment to be loaded, as in this
> example:
> 
> 0x70000001 off    0x00007f68 vaddr 0x00008150 paddr 0x00008150 align 2**2
>          filesz 0x00000008 memsz 0x00000008 flags r--
>     LOAD off    0x000000f4 vaddr 0x00000000 paddr 0x00000000 align 2**2
>          filesz 0x00000124 memsz 0x00000124 flags r--
>     LOAD off    0x00000218 vaddr 0x00000400 paddr 0x00000400 align 2**3
>          filesz 0x00007d58 memsz 0x00007d58 flags r-x
>     LOAD off    0x00007f70 vaddr 0x20000140 paddr 0x00008158 align 2**3
>          filesz 0x00000a80 memsz 0x000022f8 flags rw-
>     LOAD off    0x000089f0 vaddr 0x20002438 paddr 0x00008bd8 align 2**0
>          filesz 0x00000000 memsz 0x00004000 flags rw-
>     LOAD off    0x000089f0 vaddr 0x20000000 paddr 0x20000000 align 2**0
>          filesz 0x00000000 memsz 0x00000140 flags rw-
> 
> where the segment at paddr 0x8158 has a memsz of 0x2258 and
> would overlap with the segment at paddr 0x8bd8 if QEMU's loader
> tried to honour it. (At runtime the segments will not overlap
> since their vaddrs are more widely spaced than their paddrs.)
> 
> Currently if you try to load an ELF file like this with QEMU then
> it will fail with an error "rom: requested regions overlap",
> because we create a ROM image for each segment using the memsz
> as the size.
> 
> Support ELF files using this scheme, by truncating the
> zero-initialized part of the segment if it would overlap another
> segment. This will retain the existing loader behaviour for
> all ELF files we currently accept, and also accept ELF files
> which only need 'filesz' bytes to be loaded.
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  include/hw/elf_ops.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)

Reviewed-by: Richard Henderson <address@hidden>


r~