Re: [Qemu-devel] Configuring QEMU to translate x86 instructions to native ARM instructions

[Peter Maydell]

On 6 March 2012 05:11, Roger Tagged <address@hidden> wrote:
> I want to use the CPU emulation component of QEMU (user mode) and I'm
> running into a bit of a problem that I hope you can help me with or point me
> to the right list.

Which version of QEMU are you using?

> On my x86 Linux VM, I have configured QEMU with:
>
> '--target-list=i386-linux-user' '--cc=/bin/arm-none-linux-gnueabi-gcc

You should use '--cross-prefix=arm-none-linux-gnueabi-' instead of
specifying --cc, so qemu uses the whole cross toolchain rather than
just the gcc...

> I then issue the make command which cross-compiles the source code to run on
> an ARM CPU to emulate an x86 CPU.  When I debug the resulting ARM code, I
> can see that QEMU successfully turns an x86 instruction into the
> intermediate micro operations.  When the first call is reach, the
> translation ends and it then attempts to executed the micro operations as
> host (should be ARM) code which crashes with an illegal instruction
>
> Program received signal SIGILL, Illegal instruction.
> 0x402a4360 in code_gen_prologue
>
> When I disassemble code_gen_prologue, I expected to see ARM instructions,
> but I am not.
>
> (gdb) disassem code_gen_prologue
> Dump of assembler code for function code_gen_prologue:
> => 0x402a4360 <+0>:   ; <UNDEFINED> instruction: 0x57565355
>    0x402a4364 <+4>: ldc2l 4, cr12, [r4, #-516]! ; 0xfffffdfc
>    0x402a4368 <+8>: stm r11, {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, r10,
> r11, r12, sp, lr, pc}
>    0x402a436c <+12>: strgt lr, [r1], #767 ; 0x2ff
> Why don't I see ARM instructions here?  Is the prologue being generated for
> x86 instead of ARM?  One thing that I know for certain is that the code that
> initializes the TCGContext tcg_target_qemu_prologue() is from the file
> tcg/i386/tcg-target.c and not from tcg/arm/tcg-target.c.  Is this the right?

How do you know this for certain?

The prologue code is written by tcg_prologue_init(), which calls
tcg_target_qemu_prologue(), which is a function provided by the TCG
backend. In this case it should be the one in tcg/arm/tcg-target.c.

-- PMM