[Qemu-devel] Re: [RFC] OSX/ppc64 TCG support

[malc]

On Sat, 11 Apr 2009, Andreas F?rber wrote:

> Hello,
> 
> I've tried to add TCG backend support for Mac OS X ppc64 with limited success.
> It seems the linkage area and LR offset are the same as on Linux, so the main
> difference I could find was the register usage.
> 
> This brought up two questions:
> 
> i) In ppc/tcg-target.c TCG_REG_R2 is listed twice in
> tcg_target_reg_alloc_order for __APPLE__. I assume this is not intended? It
> does so far work with or without this patch eliminating the second use:

Not intended, thanks for noticing.

> 
> diff --git a/tcg/ppc/tcg-target.c b/tcg/ppc/tcg-target.c
> index 23f94a8..7607d85 100644
> --- a/tcg/ppc/tcg-target.c
> +++ b/tcg/ppc/tcg-target.c
> @@ -114,7 +114,9 @@ static const int tcg_target_reg_alloc_order[] = {
> #endif
>     TCG_REG_R0,
>     TCG_REG_R1,
> +#ifndef __APPLE__
>     TCG_REG_R2,
> +#endif
>     TCG_REG_R24,
>     TCG_REG_R25,
>     TCG_REG_R26,
> 
> Alternatively, if the order of r2 does not matter too much, we could 
> remove the initial __APPLE__ section instead for simplicity.
> 
> ii) In ppc64/tcg-target.c tcg_target_call_oarg_regs is declared with a 
> length of 2 but only contains one register. Intended?

Probably not, then again i'd have to recheck PPC64 ABI for DI/struct
returns to be sure, then again QEMU doesn't sue those. Anyhow...
 
> diff --git a/tcg/ppc64/tcg-target.c b/tcg/ppc64/tcg-target.c
> index a96314c..2a8eaec 100644
> --- a/tcg/ppc64/tcg-target.c
> +++ b/tcg/ppc64/tcg-target.c
> @@ -125,11 +134,15 @@ static const int tcg_target_call_iarg_regs[] = {
>     TCG_REG_R10
> };
> 
> -static const int tcg_target_call_oarg_regs[2] = {
> +static const int tcg_target_call_oarg_regs[1] = {
>     TCG_REG_R3
> };

This is most certainly is just as in correct as having it at [2] and
not initializing element N1 since main tcg proper never invokes ARRAY_SIZE
on tcg_target_call_oarg_regs...

> 
> Then for the real OSX/ppc64 changes, I have marked r11 and r13 
> callee-saved, like for OSX/ppc. Reference: 
> http://developer.apple.com/documentation/DeveloperTools/Conceptual/LowLevelABI/110-64-bit_PowerPC_Function_Calling_Conventions/64bitPowerPC.html
> 
> To my knowledge in ppc64 mode (at least on the G5) the lmw and stmw
> instructions are illegal. We should probably remove their definitions, they
> are not currently being used in the ppc64 backend.

They aren't used in PPC32 case either, i'll whack them.

> Unfortunately qemu-system-ppc still crashes immediately, any hints welcome.
> 
> Program received signal EXC_BAD_INSTRUCTION, Illegal instruction/operand.
> 0x00000000005a9680 in code_gen_prologue ()
> (gdb) bt

I think TOCs are a lot different in ppc-elf64abi and Mach-O one, that
would explain why it fails so early

> #0  0x00000000005a9680 in code_gen_prologue ()

[..snip..]

Unfortunatelly i don't have access to MacOSX on a PPC64 so you are on your
own there.

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