Re: [Qemu-devel] [v2 PATCH] target-mips: implement UserLocal Register

[Andreas Färber]

Am 26.05.2014 19:28, schrieb Petar Jovanovic:
> From: Petar Jovanovic <address@hidden>
> 
> From MIPS documentation (Volume III):
> 
> UserLocal Register (CP0 Register 4, Select 2)
> Compliance Level: Recommended.
> 
> The UserLocal register is a read-write register that is not interpreted by
> the hardware and conditionally readable via the RDHWR instruction.
> 
> This register only exists if the Config3-ULRI register field is set.
> 
> Privileged software may write this register with arbitrary information and
> make it accessable to unprivileged software via register 29 (ULR) of the

"accessible"

> RDHWR instruction. To do so, bit 29 of the HWREna register must be set to a
> 1 to enable unprivileged access to the register.
> 
> Signed-off-by: Petar Jovanovic <address@hidden>
> ---
> v2:
> - Defined MIPS_HFLAG_CP0UL flag, checks are now based on hflags
> - CP0_UserLocal moved to struct TCState
> - Added tc->CP0_UserLocal in save_tc/load_tc in target-mips/machine.c
> - Reused CP0_UserLocal field for user-mode purpose
[...]
> diff --git a/target-mips/machine.c b/target-mips/machine.c
> index 0a07db8..cbd9d7a 100644
> --- a/target-mips/machine.c
> +++ b/target-mips/machine.c
> @@ -25,6 +25,7 @@ static void save_tc(QEMUFile *f, TCState *tc)
>      qemu_put_betls(f, &tc->CP0_TCSchedule);
>      qemu_put_betls(f, &tc->CP0_TCScheFBack);
>      qemu_put_sbe32s(f, &tc->CP0_Debug_tcstatus);
> +    qemu_put_betls(f, &tc->CP0_UserLocal);
>  }
>  
>  static void save_fpu(QEMUFile *f, CPUMIPSFPUContext *fpu)
> @@ -173,6 +174,7 @@ static void load_tc(QEMUFile *f, TCState *tc)
>      qemu_get_betls(f, &tc->CP0_TCSchedule);
>      qemu_get_betls(f, &tc->CP0_TCScheFBack);
>      qemu_get_sbe32s(f, &tc->CP0_Debug_tcstatus);
> +    qemu_get_betls(f, &tc->CP0_UserLocal);
>  }
>  
>  static void load_fpu(QEMUFile *f, CPUMIPSFPUContext *fpu)

You can't just add fields here. When loading you'll need to check the
version you're loading for whether or not to load the field, and for
saving you need to increment the version.

Otherwise looks sensible.

Regards,
Andreas

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