[Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Julia Suvorova]

ARMv6-M supports 6 Thumb2 instructions. This patch checks for these
instructions and allows their execution.
Like Thumb2 cores, ARMv6-M always interprets BL instruction as 32-bit.

This patch is required for future Cortex-M0 support.

Signed-off-by: Julia Suvorova <jusual@mail.ru>
---
 target/arm/translate.c | 35 ++++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/target/arm/translate.c b/target/arm/translate.c
index 0ff5edf2ce..8cae3f5ed0 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9965,7 +9965,8 @@ static bool thumb_insn_is_16bit(DisasContext *s, uint32_t insn)
      * end up actually treating this as two 16-bit insns, though,
      * if it's half of a bl/blx pair that might span a page boundary.
      */
-    if (arm_dc_feature(s, ARM_FEATURE_THUMB2)) {
+    if (arm_dc_feature(s, ARM_FEATURE_THUMB2) ||
+        arm_dc_feature(s, ARM_FEATURE_M)) {
         /* Thumb2 cores (including all M profile ones) always treat
          * 32-bit insns as 32-bit.
          */
@@ -10075,6 +10076,11 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
 {
     uint32_t imm, shift, offset;
     uint32_t rd, rn, rm, rs;
+    uint32_t armv6m_insn[] = {0xf3808000 /* msr */, 0xf3b08040 /* dsb */,
+                              0xf3b08050 /* dmb */, 0xf3b08060 /* isb */,
+                              0xf3e08000 /* mrs */, 0xf000d000 /* bl */};
+    uint32_t armv6m_mask[] = {0xffe0d000, 0xfff0d0f0, 0xfff0d0f0,
+                              0xfff0d0f0, 0xffe0d000, 0xf800d000};
     TCGv_i32 tmp;
     TCGv_i32 tmp2;
     TCGv_i32 tmp3;
@@ -10085,10 +10091,25 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
     int conds;
     int logic_cc;
 
-    /* The only 32 bit insn that's allowed for Thumb1 is the combined
-     * BL/BLX prefix and suffix.
+    /*
+     * ARMv6-M supports a limited subset of Thumb2 instructions.
+     * Other Thumb1 architectures allow only 32-bit
+     * combined BL/BLX prefix and suffix.
      */
-    if ((insn & 0xf800e800) != 0xf000e800) {
+    if (arm_dc_feature(s, ARM_FEATURE_M) && arm_dc_feature(s, ARM_FEATURE_V6)) {
+        int i;
+        bool found = false;
+
+        for (i = 0; i < ARRAY_SIZE(armv6m_insn); i++) {
+            if ((insn & armv6m_mask[i]) == armv6m_insn[i]) {
+                found = true;
+                break;
+            }
+        }
+        if (!found) {
+            goto illegal_op;
+        }
+    } else if ((insn & 0xf800e800) != 0xf000e800)  {
         ARCH(6T2);
     }
 
@@ -11009,7 +11030,11 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
                         }
                         break;
                     case 3: /* Special control operations.  */
-                        ARCH(7);
+                        if (!arm_dc_feature(s, ARM_FEATURE_V7) &&
+                            !(arm_dc_feature(s, ARM_FEATURE_V6) &&
+                              arm_dc_feature(s, ARM_FEATURE_M))) {
+                            goto illegal_op;
+                        }
                         op = (insn >> 4) & 0xf;
                         switch (op) {
                         case 2: /* clrex */
-- 
2.17.0

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Stefan Hajnoczi]

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On Tue, Jun 12, 2018 at 11:46:32PM +0300, Julia Suvorova wrote:
> ARMv6-M supports 6 Thumb2 instructions. This patch checks for these
> instructions and allows their execution.
> Like Thumb2 cores, ARMv6-M always interprets BL instruction as 32-bit.
> 
> This patch is required for future Cortex-M0 support.
> 
> Signed-off-by: Julia Suvorova <jusual@mail.ru>
> ---
>  target/arm/translate.c | 35 ++++++++++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 5 deletions(-)

Does make the undefined instruction test case that I recently posted
pass (including all commented out instructions that weren't working
yet)?

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Julia Suvorova]

On 13.06.2018 17:05, Stefan Hajnoczi wrote:
> On Tue, Jun 12, 2018 at 11:46:32PM +0300, Julia Suvorova wrote:
>> ARMv6-M supports 6 Thumb2 instructions. This patch checks for these
>> instructions and allows their execution.
>> Like Thumb2 cores, ARMv6-M always interprets BL instruction as 32-bit.
>>
>> This patch is required for future Cortex-M0 support.
>>
>> Signed-off-by: Julia Suvorova <jusual@mail.ru>
>> ---
>>   target/arm/translate.c | 35 ++++++++++++++++++++++++++++++-----
>>   1 file changed, 30 insertions(+), 5 deletions(-)
> 
> Does make the undefined instruction test case that I recently posted
> pass (including all commented out instructions that weren't working
> yet)?
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> 

Yes, test with all instructions is passed.

Best regards, Julia Suvorova.

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Stefan Hajnoczi]

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On Wed, Jun 13, 2018 at 08:10:23PM +0300, Julia Suvorova via Qemu-devel wrote:
> On 13.06.2018 17:05, Stefan Hajnoczi wrote:
> > On Tue, Jun 12, 2018 at 11:46:32PM +0300, Julia Suvorova wrote:
> > > ARMv6-M supports 6 Thumb2 instructions. This patch checks for these
> > > instructions and allows their execution.
> > > Like Thumb2 cores, ARMv6-M always interprets BL instruction as 32-bit.
> > > 
> > > This patch is required for future Cortex-M0 support.
> > > 
> > > Signed-off-by: Julia Suvorova <jusual@mail.ru>
> > > ---
> > >   target/arm/translate.c | 35 ++++++++++++++++++++++++++++++-----
> > >   1 file changed, 30 insertions(+), 5 deletions(-)
> > 
> > Does make the undefined instruction test case that I recently posted
> > pass (including all commented out instructions that weren't working
> > yet)?
> > 
> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > 
> 
> Yes, test with all instructions is passed.

Great, I have sent a v2 of that patch.  It now also includes the 6 valid
32-bit instructions to prove that your patch has enabled them.

Stefan

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Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Peter Maydell]

On 12 June 2018 at 21:46, Julia Suvorova <jusual@mail.ru> wrote:
> ARMv6-M supports 6 Thumb2 instructions. This patch checks for these
> instructions and allows their execution.
> Like Thumb2 cores, ARMv6-M always interprets BL instruction as 32-bit.
>
> This patch is required for future Cortex-M0 support.
>
> Signed-off-by: Julia Suvorova <jusual@mail.ru>
> @@ -10075,6 +10076,11 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
>  {
>      uint32_t imm, shift, offset;
>      uint32_t rd, rn, rm, rs;
> +    uint32_t armv6m_insn[] = {0xf3808000 /* msr */, 0xf3b08040 /* dsb */,
> +                              0xf3b08050 /* dmb */, 0xf3b08060 /* isb */,
> +                              0xf3e08000 /* mrs */, 0xf000d000 /* bl */};
> +    uint32_t armv6m_mask[] = {0xffe0d000, 0xfff0d0f0, 0xfff0d0f0,
> +                              0xfff0d0f0, 0xffe0d000, 0xf800d000};

I think these arrays should be 'const'; we can also move them closer
to their point of use, inside the scope of the if() below.

Since those are trivial tweaks, I'm going to put this into
target-arm.next with those changes made, if that's OK.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Julia Suvorova]

On 15.06.2018 13:55, Peter Maydell wrote:
> On 12 June 2018 at 21:46, Julia Suvorova <jusual@mail.ru> wrote:
>> ARMv6-M supports 6 Thumb2 instructions. This patch checks for these
>> instructions and allows their execution.
>> Like Thumb2 cores, ARMv6-M always interprets BL instruction as 32-bit.
>>
>> This patch is required for future Cortex-M0 support.
>>
>> Signed-off-by: Julia Suvorova <jusual@mail.ru>
>> @@ -10075,6 +10076,11 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
>>   {
>>       uint32_t imm, shift, offset;
>>       uint32_t rd, rn, rm, rs;
>> +    uint32_t armv6m_insn[] = {0xf3808000 /* msr */, 0xf3b08040 /* dsb */,
>> +                              0xf3b08050 /* dmb */, 0xf3b08060 /* isb */,
>> +                              0xf3e08000 /* mrs */, 0xf000d000 /* bl */};
>> +    uint32_t armv6m_mask[] = {0xffe0d000, 0xfff0d0f0, 0xfff0d0f0,
>> +                              0xfff0d0f0, 0xffe0d000, 0xf800d000};
> 
> I think these arrays should be 'const'; we can also move them closer
> to their point of use, inside the scope of the if() below.
> 
> Since those are trivial tweaks, I'm going to put this into
> target-arm.next with those changes made, if that's OK.

Sure, thanks.

Best regards, Julia Suvorova.

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Richard Henderson]

On 06/15/2018 12:55 AM, Peter Maydell wrote:
>> +    uint32_t armv6m_insn[] = {0xf3808000 /* msr */, 0xf3b08040 /* dsb */,
>> +                              0xf3b08050 /* dmb */, 0xf3b08060 /* isb */,
>> +                              0xf3e08000 /* mrs */, 0xf000d000 /* bl */};
>> +    uint32_t armv6m_mask[] = {0xffe0d000, 0xfff0d0f0, 0xfff0d0f0,
>> +                              0xfff0d0f0, 0xffe0d000, 0xf800d000};
> I think these arrays should be 'const'; we can also move them closer
> to their point of use, inside the scope of the if() below.

static as well.


r~

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Peter Maydell]

On 17 June 2018 at 06:36, Richard Henderson
<richard.henderson@linaro.org> wrote:
> On 06/15/2018 12:55 AM, Peter Maydell wrote:
>>> +    uint32_t armv6m_insn[] = {0xf3808000 /* msr */, 0xf3b08040 /* dsb */,
>>> +                              0xf3b08050 /* dmb */, 0xf3b08060 /* isb */,
>>> +                              0xf3e08000 /* mrs */, 0xf000d000 /* bl */};
>>> +    uint32_t armv6m_mask[] = {0xffe0d000, 0xfff0d0f0, 0xfff0d0f0,
>>> +                              0xfff0d0f0, 0xffe0d000, 0xf800d000};
>> I think these arrays should be 'const'; we can also move them closer
>> to their point of use, inside the scope of the if() below.
>
> static as well.

Mmm; commit is already in master though, will need a followup patch.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Julia Suvorova]

On 17.06.2018 19:33, Peter Maydell wrote:
> On 17 June 2018 at 06:36, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>> On 06/15/2018 12:55 AM, Peter Maydell wrote:
>>>> +    uint32_t armv6m_insn[] = {0xf3808000 /* msr */, 0xf3b08040 /* dsb */,
>>>> +                              0xf3b08050 /* dmb */, 0xf3b08060 /* isb */,
>>>> +                              0xf3e08000 /* mrs */, 0xf000d000 /* bl */};
>>>> +    uint32_t armv6m_mask[] = {0xffe0d000, 0xfff0d0f0, 0xfff0d0f0,
>>>> +                              0xfff0d0f0, 0xffe0d000, 0xf800d000};
>>> I think these arrays should be 'const'; we can also move them closer
>>> to their point of use, inside the scope of the if() below.
>>
>> static as well.
> 
> Mmm; commit is already in master though, will need a followup patch.

I can make it if you wish.
In addition, we can simplify following "if" by removing ARM_FEATURE_V6
since V7M and V8M define V6:

     if (!arm_dc_feature(s, ARM_FEATURE_V7) &&
         !(arm_dc_feature(s, ARM_FEATURE_V6) &&
           arm_dc_feature(s, ARM_FEATURE_M))) {
         goto illegal_op;
     }

Like this:

     if (!arm_dc_feature(s, ARM_FEATURE_V7) &&
         !arm_dc_feature(s, ARM_FEATURE_M)) {
         goto illegal_op;
     }

What do you think?

Best regards, Julia Suvorova.

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Peter Maydell]

On 17 June 2018 at 19:48, Julia Suvorova <jusual@mail.ru> wrote:
> I can make it if you wish.
> In addition, we can simplify following "if" by removing ARM_FEATURE_V6
> since V7M and V8M define V6:
>
>     if (!arm_dc_feature(s, ARM_FEATURE_V7) &&
>         !(arm_dc_feature(s, ARM_FEATURE_V6) &&
>           arm_dc_feature(s, ARM_FEATURE_M))) {
>         goto illegal_op;
>     }
>
> Like this:
>
>     if (!arm_dc_feature(s, ARM_FEATURE_V7) &&
>         !arm_dc_feature(s, ARM_FEATURE_M)) {
>         goto illegal_op;
>     }
>
> What do you think?

Yes; that would be reasonable. I did consider making that
change when I applied the patch, but decided I didn't really
care much either way. So if you want to send a patch for it
that's fine; if you don't, that's also fine.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] target/arm: Allow ARMv6-M Thumb2 instructions

[Peter Maydell]

On 12 June 2018 at 21:46, Julia Suvorova <jusual@mail.ru> wrote:
> @@ -10085,10 +10091,25 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
>      int conds;
>      int logic_cc;
>
> -    /* The only 32 bit insn that's allowed for Thumb1 is the combined
> -     * BL/BLX prefix and suffix.
> +    /*
> +     * ARMv6-M supports a limited subset of Thumb2 instructions.
> +     * Other Thumb1 architectures allow only 32-bit
> +     * combined BL/BLX prefix and suffix.
>       */
> -    if ((insn & 0xf800e800) != 0xf000e800) {
> +    if (arm_dc_feature(s, ARM_FEATURE_M) && arm_dc_feature(s, ARM_FEATURE_V6)) {

I realized during testing that this accidentally breaks v7M and v8M,
because those cores define both ARM_FEATURE_V6 and _V7 (and _V8 for v8M),
so this condition is true and we undef on the non-v6M insns for
v7M and v8M too. I've fixed this in target-arm.next by changing the
condition to
    +    if (arm_dc_feature(s, ARM_FEATURE_M) &&
    +        !arm_dc_feature(s, ARM_FEATURE_V7)) {

thanks
-- PMM