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Re: [Qemu-devel] [PATCH v1 13/17] arm: linux-user: don't set CPSR.E in B
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH v1 13/17] arm: linux-user: don't set CPSR.E in BE32 mode |
Date: |
Tue, 19 Jan 2016 17:35:45 +0000 |
On 19 January 2016 at 17:26, Peter Maydell <address@hidden> wrote:
> On 18 January 2016 at 07:12, Peter Crosthwaite
> <address@hidden> wrote:
>> Don't set CPSR.E for BE32 linux-user mode. As linux-user mode models
>> BE32, using normal BE (and system mode will not), a special case is
>> needed for user-mode where if sctlr.b is set, the CPU identifies as BE.
>>
>> Signed-off-by: Peter Crosthwaite <address@hidden>
>> ---
>>
>> linux-user/main.c | 2 --
>> target-arm/cpu.h | 12 +++++++++++-
>> 2 files changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/linux-user/main.c b/linux-user/main.c
>> index d481458..60375fb 100644
>> --- a/linux-user/main.c
>> +++ b/linux-user/main.c
>> @@ -4496,8 +4496,6 @@ int main(int argc, char **argv, char **envp)
>> env->uncached_cpsr |= CPSR_E;
>> } else {
>> env->cp15.sctlr_el[1] |= SCTLR_B;
>> - /* We model BE32 as regular BE, so set CPSR_E */
>> - env->uncached_cpsr |= CPSR_E;
>
> ...this is undoing what we just did in the previous patch and
> which I reviewed as being the wrong thing there...
>
>> }
>> #endif
>> }
>> diff --git a/target-arm/cpu.h b/target-arm/cpu.h
>> index 3edd56b..96b1e99 100644
>> --- a/target-arm/cpu.h
>> +++ b/target-arm/cpu.h
>> @@ -1812,7 +1812,17 @@ static bool arm_cpu_is_big_endian(CPUARMState *env)
>>
>> /* In 32bit endianness is determined by looking at CPSR's E bit */
>> if (!is_a64(env)) {
>> - return (env->uncached_cpsr & CPSR_E) ? 1 : 0;
>> + return
>> +#ifdef CONFIG_USER_ONLY
>> + /* In user mode, BE32 data accesses are just modelled as
>> + * regular BE access. In system mode, BE32 is modelled as
>> + * little endian, with the appropriate address translations on
>> + * non-word accesses. So sctlr.b only affects overall
>> + * endianness in user mode
>> + */
>> + arm_sctlr_b(env) ||
>> +#endif
>> + ((env->uncached_cpsr & CPSR_E) ? 1 : 0);
>> }
>
> This doesn't seem quite right -- for system emulation we currently
> pick MO_BE or MO_LE based on the TB flag which is set according
> to (arm_cpu_is_big_endian(env). So if we ignore SCTLR.B in
> system mode then we'll still try to do LE accesses.
Ah, no, looking at the next patch this is correct, it's just the
comment is a touch confusing. I suggest
/* In system mode, BE32 is modelled in line with the architecture
* (as word-invariant big-endianness), where loads and stores are done
* little endian but from addresses which are adjusted by XORing
* with the appropriate constant. So the endianness to use for the
* raw data access is not affected by SCTLR.B.
* In user mode, however, we model BE32 as byte-invariant big-endianness
* (because user-only code cannot tell the difference), and so we
* need to use a data access endianness that depends on SCTLR.B.
*/
thanks
-- PMM
- [Qemu-devel] [PATCH v1 11/17] linux-user: arm: pass env to get_user_code_*, (continued)
- [Qemu-devel] [PATCH v1 11/17] linux-user: arm: pass env to get_user_code_*, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 07/17] target-arm: a64: Add endianness support, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 08/17] target-arm: cpu: Move cpu_is_big_endian to header, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 10/17] target-arm: implement setend, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 13/17] arm: linux-user: don't set CPSR.E in BE32 mode, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 14/17] target-arm: implement BE32 mode in system emulation, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 12/17] target-arm: implement SCTLR.B, drop bswap_code, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 16/17] loader: Add data swap option to load-elf, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 17/17] arm: boot: Support big-endian elfs, Peter Crosthwaite, 2016/01/18
- [Qemu-devel] [PATCH v1 15/17] loader: add API to load elf header, Peter Crosthwaite, 2016/01/18