[Qemu-devel] User mode issue for loading 32-bit ELF on 64-bit guest processor

["Laurent Desnogues" <laurent.desnogues@gmail.com>]

Hello,

while playing with sparc64 Linux user mode emulation, I tried
to run a 32-bit v8plus executable;  this may not work according
to Blue Swirl, but that's not the issue I had.

Currently elfload32.c forces the definition of TARGET_ABI32
before including elfload.c.  This notably results in abi_ulong
being forced as a 32-bit integer.  In turn this will change some
structure layouts such as linux_binprm and image_info which
are parameters of load_elf_binary/load_elf_binary32.  But
linuxload.c/loader_exec uses the standard 64-bit integer for
defining abi_ulong.  In the end this segfaults when accessing
fields of linux_binprm when trying to load a 32-bit ELF.

I am not sure what is the cleanest way to fix that problem.  As
a quick hack I just inserted uint32_t fields after each abi_ulong
field in linux_binprm and image_info structures when
TARGET_ABI32 is defined (I know this is not generally correct,
it was just a way to check my understanding was right).

Blue Swirl proposed to use accessors for these structures
while I proposed to use a new abi_ulong-like type that would
be the same no matter whether TARGET_ABI32 is defined or
not.  As I am not sure there aren't some other structures that
would need such a type, I think my proposal is less intrusive.
The drawback is that it would introduce a new type and we
already have many such *_ulong types :-)

What do people think?


Laurent