Re: [Qemu-devel] [PATCH 0/4] disas: add libvixl to support A64 disassembly

[Peter Maydell]

On 7 January 2014 22:30, Stefan Weil <address@hidden> wrote:
> here are some first annotations.
>
> ---
>
> Git complains because patch 3 adds blank lines at EOF:
>
> Applying: disas: add libvixl source code for AArch64 A64 disassembler
> /home/stefan/src/qemu/qemu.org/a64-vixl/.git/rebase-apply/patch:1382:
> new blank line at EOF.
> +
> /home/stefan/src/qemu/qemu.org/a64-vixl/.git/rebase-apply/patch:11354:
> new blank line at EOF.
> +
> warning: 2 lines add whitespace errors.

Doh. I saw those as I applied the patches and then forgot to
investigate and fix them.

> I'd prefer one file disas/aarch64.cc instead of these two files:
>
>  disas/aarch64-cxx.cc        |   80
> +++++++++++++++++++++++++++++++++++++++++++
>  disas/aarch64.c             |   39 +++++++++++++++++++++
>
> This would also allow removing the extern statement in the C++ code (and
> use a local function).

See the comment in aarch64-cxx.cc -- to do that we'd need to
make sure bfd.h was valid for C++ as well as C compilation. This
came up when Andreas reviewed the RFC and that was Claudio's
explanation for the split, which is why I added the comment.

Claudio -- do you recall what the exact issue here is?

Specifically, I think the problem is that if we put print_insn_aarch64()
in the C++ file then we need to have its prototype in bfd.h guarded
with "extern C {}" if (and only if) we're compiling a C++ file. If
you care about restricting the C++-isms to the C++ files that's
a bit ugly. But we could do that if people prefer.

Some experimentation suggests it would also be possible to
just do

extern "C" {
#include "disas/bfd.h"
}

in the C++ file. If that doesn't have any hidden gotchas I don't
know about it looks like the nicest solution.

> Spelling bugs:
>
> disas/libvixl/src/a64/constants-a64.h:/* Add/substract extend
> */
> substract  ==> subtract

I don't really want to mess with the upstream libvixl code too much
for preference. Unlike the binutils disassemblers, we still have the
option in future for pulling in updated versions.

> Compiler warnings (w32, w64):
>
>   CXX   disas/aarch64-cxx.o
> In file included from
> /home/stefan/src/qemu/qemu.org/a64-vixl/disas/libvixl/src/a64/simulator-a64.h:32:0,
>                  from
> /home/stefan/src/qemu/qemu.org/a64-vixl/disas/aarch64-cxx.cc:25:
> /home/stefan/src/qemu/qemu.org/a64-vixl/disas/libvixl/src/a64/instructions-a64.h:60:36:
> warning: left shift coun
> t >= width of type [enabled by default]
>
> (more of that kind for disas/libvixl/src/a64/instructions-a64.o)
>
> These warnings are caused by Windows sizeof(long) == 4, so 1L has to be
> replaced by 1LL or 1ULL to represent a 64 bit value, or use a type cast
> like (int64_t)1.

Those I think we really do need to fix, though, since they're bugs.

> I tested cross compilation for w32 and w64 (see comments below) and
> started the w32 executable (wine
> bin/debug/i686-w64-mingw32/aarch64-softmmu/qemu-system-aarch64 -L
> pc-bios --sdl).

Thanks for testing this.

thanks
-- PMM