diff mbox series

[v2,03/10] target/arm: Set disassemble_info::endian value in disas_set_info()

Message ID 20250210212931.62401-4-philmd@linaro.org
State Superseded
Headers show
Series disas: Have CPUClass::disas_set_info() callback set the endianness | expand

Commit Message

Philippe Mathieu-Daudé Feb. 10, 2025, 9:29 p.m. UTC 
Have the CPUClass::disas_set_info() callback set the
disassemble_info::endian field.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 target/arm/cpu.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

Comments

Richard Henderson Feb. 10, 2025, 10:10 p.m. UTC | #1 
On 2/10/25 13:29, Philippe Mathieu-Daudé wrote:
> Have the CPUClass::disas_set_info() callback set the
> disassemble_info::endian field.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   target/arm/cpu.c | 10 +++-------
>   1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 94f1c55622b..68b3a9d3ab0 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -1188,7 +1188,7 @@ static void arm_disas_set_info(CPUState *cpu, disassemble_info *info)
>   {
>       ARMCPU *ac = ARM_CPU(cpu);
>       CPUARMState *env = &ac->env;
> -    bool sctlr_b;
> +    bool sctlr_b = arm_sctlr_b(env);
>   
>       if (is_a64(env)) {
>           info->cap_arch = CS_ARCH_ARM64;
> @@ -1215,13 +1215,9 @@ static void arm_disas_set_info(CPUState *cpu, disassemble_info *info)
>           info->cap_mode = cap_mode;
>       }
>   
> -    sctlr_b = arm_sctlr_b(env);
> +    info->endian = BFD_ENDIAN_LITTLE;
>       if (bswap_code(sctlr_b)) {
> -#if TARGET_BIG_ENDIAN
> -        info->endian = BFD_ENDIAN_LITTLE;
> -#else
> -        info->endian = BFD_ENDIAN_BIG;
> -#endif
> +        info->endian = TARGET_BIG_ENDIAN ? BFD_ENDIAN_LITTLE : BFD_ENDIAN_BIG;
>       }
>       info->flags &= ~INSN_ARM_BE32;
>   #ifndef CONFIG_USER_ONLY

This is a faithful adjustment to the existing code, so,

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

However:

(1) aarch64 code is always little-endian,
(2) sctlr_b is always false from armv7 (and thus always false for aarch64)
(3) I think the BE32 logic is wrong -- CONFIG_USER_ONLY is irrelevant.
     See linux-user/arm/cpu_loop.c, target_cpu_copy_regs.


r~
Philippe Mathieu-Daudé Feb. 10, 2025, 10:59 p.m. UTC | #2 
On 10/2/25 23:10, Richard Henderson wrote:
> On 2/10/25 13:29, Philippe Mathieu-Daudé wrote:
>> Have the CPUClass::disas_set_info() callback set the
>> disassemble_info::endian field.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> ---
>>   target/arm/cpu.c | 10 +++-------
>>   1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>> index 94f1c55622b..68b3a9d3ab0 100644
>> --- a/target/arm/cpu.c
>> +++ b/target/arm/cpu.c
>> @@ -1188,7 +1188,7 @@ static void arm_disas_set_info(CPUState *cpu, 
>> disassemble_info *info)
>>   {
>>       ARMCPU *ac = ARM_CPU(cpu);
>>       CPUARMState *env = &ac->env;
>> -    bool sctlr_b;
>> +    bool sctlr_b = arm_sctlr_b(env);
>>       if (is_a64(env)) {
>>           info->cap_arch = CS_ARCH_ARM64;
>> @@ -1215,13 +1215,9 @@ static void arm_disas_set_info(CPUState *cpu, 
>> disassemble_info *info)
>>           info->cap_mode = cap_mode;
>>       }
>> -    sctlr_b = arm_sctlr_b(env);
>> +    info->endian = BFD_ENDIAN_LITTLE;
>>       if (bswap_code(sctlr_b)) {
>> -#if TARGET_BIG_ENDIAN
>> -        info->endian = BFD_ENDIAN_LITTLE;
>> -#else
>> -        info->endian = BFD_ENDIAN_BIG;
>> -#endif
>> +        info->endian = TARGET_BIG_ENDIAN ? BFD_ENDIAN_LITTLE : 
>> BFD_ENDIAN_BIG;
>>       }
>>       info->flags &= ~INSN_ARM_BE32;
>>   #ifndef CONFIG_USER_ONLY
> 
> This is a faithful adjustment to the existing code, so,
> 
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> 
> However:
> 
> (1) aarch64 code is always little-endian,
> (2) sctlr_b is always false from armv7 (and thus always false for aarch64)
> (3) I think the BE32 logic is wrong -- CONFIG_USER_ONLY is irrelevant.
>      See linux-user/arm/cpu_loop.c, target_cpu_copy_regs.

What about v7-R [*]? I don't see SCTLR_IE defined as 1<<31 for AArch32,
only:

#define SCTLR_EnIA    (1U << 31) /* v8.3, AArch64 only */
#define SCTLR_DSSBS_32 (1U << 31) /* v8.5, AArch32 only */

---

[*] 
https://developer.arm.com/documentation/ddi0406/cb/System-Level-Architecture/System-Control-Registers-in-a-PMSA-implementation/PMSA-System-control-registers-descriptions--in-register-order/SCTLR--System-Control-Register--PMSA

SCTLR_IE, bit[31]

Instruction Endianness. This bit indicates the endianness of the
instructions issued to the processor. The possible values of this bit are:

0: Little-endian byte ordering in the instructions.
1: Big-endian byte ordering in the instructions.

When set to 1, this bit causes the byte order of instructions to be 
reversed at runtime.

This bit is read-only. It is implementation defined which instruction 
endianness is used by an ARMv7-R implementation, and this bit must 
indicate the implemented endianness.

---

For the Cortex-r5* we have, SCTLR_IE is always 0 in reset_sctlr.

Is it OK to consider v7-R implemented as little-endian in QEMU?
Richard Henderson Feb. 10, 2025, 11:37 p.m. UTC | #3 
On 2/10/25 14:59, Philippe Mathieu-Daudé wrote:
> On 10/2/25 23:10, Richard Henderson wrote:
>> On 2/10/25 13:29, Philippe Mathieu-Daudé wrote:
>>> Have the CPUClass::disas_set_info() callback set the
>>> disassemble_info::endian field.
>>>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>>> ---
>>>   target/arm/cpu.c | 10 +++-------
>>>   1 file changed, 3 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>>> index 94f1c55622b..68b3a9d3ab0 100644
>>> --- a/target/arm/cpu.c
>>> +++ b/target/arm/cpu.c
>>> @@ -1188,7 +1188,7 @@ static void arm_disas_set_info(CPUState *cpu, disassemble_info 
>>> *info)
>>>   {
>>>       ARMCPU *ac = ARM_CPU(cpu);
>>>       CPUARMState *env = &ac->env;
>>> -    bool sctlr_b;
>>> +    bool sctlr_b = arm_sctlr_b(env);
>>>       if (is_a64(env)) {
>>>           info->cap_arch = CS_ARCH_ARM64;
>>> @@ -1215,13 +1215,9 @@ static void arm_disas_set_info(CPUState *cpu, disassemble_info 
>>> *info)
>>>           info->cap_mode = cap_mode;
>>>       }
>>> -    sctlr_b = arm_sctlr_b(env);
>>> +    info->endian = BFD_ENDIAN_LITTLE;
>>>       if (bswap_code(sctlr_b)) {
>>> -#if TARGET_BIG_ENDIAN
>>> -        info->endian = BFD_ENDIAN_LITTLE;
>>> -#else
>>> -        info->endian = BFD_ENDIAN_BIG;
>>> -#endif
>>> +        info->endian = TARGET_BIG_ENDIAN ? BFD_ENDIAN_LITTLE : BFD_ENDIAN_BIG;
>>>       }
>>>       info->flags &= ~INSN_ARM_BE32;
>>>   #ifndef CONFIG_USER_ONLY
>>
>> This is a faithful adjustment to the existing code, so,
>>
>> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>>
>> However:
>>
>> (1) aarch64 code is always little-endian,
>> (2) sctlr_b is always false from armv7 (and thus always false for aarch64)
>> (3) I think the BE32 logic is wrong -- CONFIG_USER_ONLY is irrelevant.
>>      See linux-user/arm/cpu_loop.c, target_cpu_copy_regs.
> 
> What about v7-R [*]? I don't see SCTLR_IE defined as 1<<31 for AArch32,
> only:

BE32 was a really old arm thingy, and I it was removed in armv7 (see arm_sctlr_b).
With BE8 (armv6+), instructions are always little-endian, only data accesses change.

> For the Cortex-r5* we have, SCTLR_IE is always 0 in reset_sctlr.
> 
> Is it OK to consider v7-R implemented as little-endian in QEMU?

Yes.


r~
diff mbox series

Patch

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 94f1c55622b..68b3a9d3ab0 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1188,7 +1188,7 @@  static void arm_disas_set_info(CPUState *cpu, disassemble_info *info)
 {
     ARMCPU *ac = ARM_CPU(cpu);
     CPUARMState *env = &ac->env;
-    bool sctlr_b;
+    bool sctlr_b = arm_sctlr_b(env);
 
     if (is_a64(env)) {
         info->cap_arch = CS_ARCH_ARM64;
@@ -1215,13 +1215,9 @@  static void arm_disas_set_info(CPUState *cpu, disassemble_info *info)
         info->cap_mode = cap_mode;
     }
 
-    sctlr_b = arm_sctlr_b(env);
+    info->endian = BFD_ENDIAN_LITTLE;
     if (bswap_code(sctlr_b)) {
-#if TARGET_BIG_ENDIAN
-        info->endian = BFD_ENDIAN_LITTLE;
-#else
-        info->endian = BFD_ENDIAN_BIG;
-#endif
+        info->endian = TARGET_BIG_ENDIAN ? BFD_ENDIAN_LITTLE : BFD_ENDIAN_BIG;
     }
     info->flags &= ~INSN_ARM_BE32;
 #ifndef CONFIG_USER_ONLY