[PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Brian Cain]

Some registers are defined to have immutable bits, this commit
will implement that behavior.

Signed-off-by: Brian Cain <bcain@quicinc.com>
---
 target/hexagon/gen_masked.c       |  44 ++++++++++++
 target/hexagon/gen_masked.h       |  26 ++++++++
 target/hexagon/genptr.c           |  33 ++++++++-
 target/hexagon/hex_regs.h         |   6 ++
 target/hexagon/meson.build        |   1 +
 tests/tcg/hexagon/Makefile.target |   1 +
 tests/tcg/hexagon/reg_mut.c       | 107 ++++++++++++++++++++++++++++++
 7 files changed, 217 insertions(+), 1 deletion(-)
 create mode 100644 target/hexagon/gen_masked.c
 create mode 100644 target/hexagon/gen_masked.h
 create mode 100644 tests/tcg/hexagon/reg_mut.c

diff --git a/target/hexagon/gen_masked.c b/target/hexagon/gen_masked.c
new file mode 100644
index 0000000000..faffee2e13
--- /dev/null
+++ b/target/hexagon/gen_masked.c
@@ -0,0 +1,44 @@
+/*
+ *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+#include "tcg/tcg-op.h"
+#include "gen_masked.h"
+
+void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
+    target_ulong reg_mask) {
+    TCGv set_bits = tcg_temp_new();
+    TCGv cleared_bits = tcg_temp_new();
+
+    /*
+     * set_bits = in_val & reg_mask
+     * cleared_bits = (~in_val) & reg_mask
+     */
+    tcg_gen_andi_tl(set_bits, in_val, reg_mask);
+    tcg_gen_not_tl(cleared_bits, in_val);
+    tcg_gen_andi_tl(cleared_bits, cleared_bits, reg_mask);
+
+    /*
+     * result = (reg_cur | set_bits) & (~cleared_bits)
+     */
+    tcg_gen_not_tl(cleared_bits, cleared_bits);
+    tcg_gen_or_tl(set_bits, set_bits, cur_val);
+    tcg_gen_and_tl(out_val, set_bits, cleared_bits);
+
+    tcg_temp_free(set_bits);
+    tcg_temp_free(cleared_bits);
+}
diff --git a/target/hexagon/gen_masked.h b/target/hexagon/gen_masked.h
new file mode 100644
index 0000000000..71f4b2818b
--- /dev/null
+++ b/target/hexagon/gen_masked.h
@@ -0,0 +1,26 @@
+/*
+ *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GEN_MASKED_H
+#define GEN_MASKED_H
+
+#include "tcg/tcg-op.h"
+
+void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
+    target_ulong reg_mask);
+
+#endif /* GEN_MASKED_H */
diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c
index 8a334ba07b..21385f556e 100644
--- a/target/hexagon/genptr.c
+++ b/target/hexagon/genptr.c
@@ -29,6 +29,7 @@
 #undef QEMU_GENERATE
 #include "gen_tcg.h"
 #include "gen_tcg_hvx.h"
+#include "gen_masked.h"
 
 static inline void gen_log_predicated_reg_write(int rnum, TCGv val, int slot)
 {
@@ -53,9 +54,24 @@ static inline void gen_log_predicated_reg_write(int rnum, TCGv val, int slot)
     tcg_temp_free(slot_mask);
 }
 
+static const hexagon_mut_entry gpr_mut_masks[HEX_REG_LAST_VALUE] = {
+    [HEX_REG_PC] = {true, 0x00000000},
+    [HEX_REG_GP] = {true, 0xffffffc0},
+    [HEX_REG_USR] = {true, 0x3ecfff3f},
+    [HEX_REG_UTIMERLO] = {true, 0x00000000},
+    [HEX_REG_UTIMERHI] = {true, 0x00000000},
+};
+
+
 static inline void gen_log_reg_write(int rnum, TCGv val)
 {
-    tcg_gen_mov_tl(hex_new_value[rnum], val);
+    const hexagon_mut_entry entry = gpr_mut_masks[rnum];
+    if (entry.present) {
+        gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum],
+            entry.mask);
+    } else {
+        tcg_gen_mov_tl(hex_new_value[rnum], val);
+    }
     if (HEX_DEBUG) {
         /* Do this so HELPER(debug_commit_end) will know */
         tcg_gen_movi_tl(hex_reg_written[rnum], 1);
@@ -64,18 +80,32 @@ static inline void gen_log_reg_write(int rnum, TCGv val)
 
 static void gen_log_predicated_reg_write_pair(int rnum, TCGv_i64 val, int slot)
 {
+    const hexagon_mut_entry entry0 = gpr_mut_masks[rnum];
+    const hexagon_mut_entry entry1 = gpr_mut_masks[rnum + 1];
     TCGv val32 = tcg_temp_new();
     TCGv zero = tcg_constant_tl(0);
     TCGv slot_mask = tcg_temp_new();
+    TCGv tmp_val = tcg_temp_new();
 
     tcg_gen_andi_tl(slot_mask, hex_slot_cancelled, 1 << slot);
+
     /* Low word */
     tcg_gen_extrl_i64_i32(val32, val);
+    if (entry0.present) {
+        tcg_gen_mov_tl(tmp_val, val32);
+        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry0.mask);
+        tcg_temp_free(tmp_val);
+    }
     tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum],
                        slot_mask, zero,
                        val32, hex_new_value[rnum]);
+
     /* High word */
     tcg_gen_extrh_i64_i32(val32, val);
+    if (entry1.present) {
+        tcg_gen_mov_tl(tmp_val, val32);
+        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry1.mask);
+    }
     tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum + 1],
                        slot_mask, zero,
                        val32, hex_new_value[rnum + 1]);
@@ -95,6 +125,7 @@ static void gen_log_predicated_reg_write_pair(int rnum, TCGv_i64 val, int slot)
 
     tcg_temp_free(val32);
     tcg_temp_free(slot_mask);
+    tcg_temp_free(tmp_val);
 }
 
 static void gen_log_reg_write_pair(int rnum, TCGv_i64 val)
diff --git a/target/hexagon/hex_regs.h b/target/hexagon/hex_regs.h
index a63c2c0fd5..db48cff96e 100644
--- a/target/hexagon/hex_regs.h
+++ b/target/hexagon/hex_regs.h
@@ -79,6 +79,12 @@ enum {
     HEX_REG_QEMU_HVX_CNT      = 54,
     HEX_REG_UTIMERLO          = 62,
     HEX_REG_UTIMERHI          = 63,
+    HEX_REG_LAST_VALUE        = 64,
 };
 
+
+typedef struct {
+    bool present;
+    target_ulong mask;
+} hexagon_mut_entry;
 #endif
diff --git a/target/hexagon/meson.build b/target/hexagon/meson.build
index b61243103f..ea1f66982a 100644
--- a/target/hexagon/meson.build
+++ b/target/hexagon/meson.build
@@ -168,6 +168,7 @@ hexagon_ss.add(files(
     'op_helper.c',
     'gdbstub.c',
     'genptr.c',
+    'gen_masked.c',
     'reg_fields.c',
     'decode.c',
     'iclass.c',
diff --git a/tests/tcg/hexagon/Makefile.target b/tests/tcg/hexagon/Makefile.target
index 96a4d7a614..385d787a00 100644
--- a/tests/tcg/hexagon/Makefile.target
+++ b/tests/tcg/hexagon/Makefile.target
@@ -43,6 +43,7 @@ HEX_TESTS += load_align
 HEX_TESTS += atomics
 HEX_TESTS += fpstuff
 HEX_TESTS += overflow
+HEX_TESTS += reg_mut
 
 TESTS += $(HEX_TESTS)
 
diff --git a/tests/tcg/hexagon/reg_mut.c b/tests/tcg/hexagon/reg_mut.c
new file mode 100644
index 0000000000..7e81ec6bf3
--- /dev/null
+++ b/tests/tcg/hexagon/reg_mut.c
@@ -0,0 +1,107 @@
+/*
+ *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+
+int err;
+
+#define check_ne(N, EXPECT) \
+    { uint32_t value = N; \
+        if (value == EXPECT) { \
+            printf("ERROR: \"%s\" 0x%04x == 0x%04x at %s:%d\n", #N, value, \
+                EXPECT, __FILE__, __LINE__); \
+            err++; \
+        } \
+    }
+
+#define check(N, EXPECT) \
+    { uint32_t value = N; \
+        if (value != EXPECT) { \
+            printf("ERROR: \"%s\" 0x%04x != 0x%04x at %s:%d\n", #N, value, \
+                  EXPECT, __FILE__, __LINE__); \
+            err++; \
+        } \
+    }
+
+#define READ_REG(reg_name, out_reg) \
+  asm volatile ("%0 = " reg_name "\n\t" \
+                : "=r"(out_reg) \
+                : \
+                : \
+                ); \
+
+#define WRITE_REG(reg_name, out_reg, in_reg) \
+  asm volatile (reg_name " = %1\n\t" \
+                "%0 = " reg_name "\n\t" \
+                : "=r"(out_reg) \
+                : "r"(in_reg) \
+                : reg_name \
+                ); \
+
+   /*
+    * Instruction word: { pc = r0 }
+    *
+    * This instruction is barred by the assembler.
+    *
+    *    3                   2                   1
+    *  1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+    * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    * |    Opc[A2_tfrrcr]   | Src[R0] |P P|                 |  C9/PC  |
+    * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    */
+#define PC_EQ_R0 ".word 0x6220c009\n\t"
+
+static inline uint32_t set_pc(uint32_t in_reg)
+{
+    uint32_t out_reg;
+    asm volatile("r0 = %1\n\t"
+                 PC_EQ_R0
+                 "%0 = pc\n\t"
+                : "=r"(out_reg)
+                : "r"(in_reg)
+                : "r0");
+    return out_reg;
+}
+
+static inline uint32_t set_usr(uint32_t in_reg)
+{
+    uint32_t out_reg;
+    WRITE_REG("usr", out_reg, in_reg);
+    return out_reg;
+}
+
+int main()
+{
+    check(set_usr(0x00),       0x00);
+    check(set_usr(0xffffffff), 0x3ecfff3f);
+    check(set_usr(0x00),       0x00);
+    check(set_usr(0x01),       0x01);
+    check(set_usr(0xff),       0x3f);
+
+    /*
+     * PC is special.  Setting it to these values
+     * should cause an instruction fetch miss.
+     */
+    check_ne(set_pc(0x00000000), 0x00000000);
+    check_ne(set_pc(0xffffffff), 0xffffffff);
+    check_ne(set_pc(0x00000001), 0x00000001);
+    check_ne(set_pc(0x000000ff), 0x000000ff);
+
+    puts(err ? "FAIL" : "PASS");
+    return err;
+}
-- 
2.35.3

Re: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Anton Johansson via]

Hi, Brian!

I've taken a look and most of this patch seems good, however I have a few
comments/observations.

> Some registers are defined to have immutable bits, this commit
> will implement that behavior.
>
> Signed-off-by: Brian Cain <bcain@quicinc.com>
> ---
>   target/hexagon/gen_masked.c       |  44 ++++++++++++
>   target/hexagon/gen_masked.h       |  26 ++++++++
>   target/hexagon/genptr.c           |  33 ++++++++-
>   target/hexagon/hex_regs.h         |   6 ++
>   target/hexagon/meson.build        |   1 +
>   tests/tcg/hexagon/Makefile.target |   1 +
>   tests/tcg/hexagon/reg_mut.c       | 107 ++++++++++++++++++++++++++++++
>   7 files changed, 217 insertions(+), 1 deletion(-)
>   create mode 100644 target/hexagon/gen_masked.c
>   create mode 100644 target/hexagon/gen_masked.h
>   create mode 100644 tests/tcg/hexagon/reg_mut.c
>
> diff --git a/target/hexagon/gen_masked.c b/target/hexagon/gen_masked.c
> new file mode 100644
> index 0000000000..faffee2e13
> --- /dev/null
> +++ b/target/hexagon/gen_masked.c
> @@ -0,0 +1,44 @@
> +/*
> + *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
> + *
> + *  This program is free software; you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation; either version 2 of the License, or
> + *  (at your option) any later version.
> + *
> + *  This program is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "tcg/tcg-op.h"
> +#include "gen_masked.h"
> +
> +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
> +    target_ulong reg_mask) {

Brace on new line per coding standard. Also I would line up the 
indentation with
the rest of the arguments to match the rest of the hexagon frontend. I would
suggest putting output arguments first to match other TCG ops, could become
confusing otherwise, so

     void gen_masked_reg_write(TCGv out_val, TCGv in_val, TCGv cur_val,
                               target_ulong reg_mask)
     {

> +    TCGv set_bits = tcg_temp_new();
> +    TCGv cleared_bits = tcg_temp_new();
> +
> +    /*
> +     * set_bits = in_val & reg_mask
> +     * cleared_bits = (~in_val) & reg_mask
> +     */
> +    tcg_gen_andi_tl(set_bits, in_val, reg_mask);
> +    tcg_gen_not_tl(cleared_bits, in_val);
> +    tcg_gen_andi_tl(cleared_bits, cleared_bits, reg_mask);
> +
> +    /*
> +     * result = (reg_cur | set_bits) & (~cleared_bits)
> +     */
> +    tcg_gen_not_tl(cleared_bits, cleared_bits);
> +    tcg_gen_or_tl(set_bits, set_bits, cur_val);
> +    tcg_gen_and_tl(out_val, set_bits, cleared_bits);
> +
> +    tcg_temp_free(set_bits);
> +    tcg_temp_free(cleared_bits);
> +}

You could cut down on a single not operation in this function since

     ~cleared_bits = ~((~in_val) & reg_mask)
                   = in_val | (~reg_mask)

I looked at the output of qemu-hexagon -d op_opt and this operation
is not performed by the TCG optimizer, so we would end up saving
an instruction.

> diff --git a/target/hexagon/gen_masked.h b/target/hexagon/gen_masked.h
> new file mode 100644
> index 0000000000..71f4b2818b
> --- /dev/null
> +++ b/target/hexagon/gen_masked.h
> @@ -0,0 +1,26 @@
> +/*
> + *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
> + *
> + *  This program is free software; you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation; either version 2 of the License, or
> + *  (at your option) any later version.
> + *
> + *  This program is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef GEN_MASKED_H
> +#define GEN_MASKED_H
> +
> +#include "tcg/tcg-op.h"
> +
> +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
> +    target_ulong reg_mask);
> +
> +#endif /* GEN_MASKED_H */
> diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c
> index 8a334ba07b..21385f556e 100644
> --- a/target/hexagon/genptr.c
> +++ b/target/hexagon/genptr.c
> @@ -29,6 +29,7 @@
>   #undef QEMU_GENERATE
>   #include "gen_tcg.h"
>   #include "gen_tcg_hvx.h"
> +#include "gen_masked.h"
>   
>   static inline void gen_log_predicated_reg_write(int rnum, TCGv val, int slot)
>   {
> @@ -53,9 +54,24 @@ static inline void gen_log_predicated_reg_write(int rnum, TCGv val, int slot)
>       tcg_temp_free(slot_mask);
>   }
>   
> +static const hexagon_mut_entry gpr_mut_masks[HEX_REG_LAST_VALUE] = {
> +    [HEX_REG_PC] = {true, 0x00000000},
> +    [HEX_REG_GP] = {true, 0xffffffc0},
> +    [HEX_REG_USR] = {true, 0x3ecfff3f},
> +    [HEX_REG_UTIMERLO] = {true, 0x00000000},
> +    [HEX_REG_UTIMERHI] = {true, 0x00000000},
> +};
> +
> +

Remove extra newline.

Also I notice

     gen_log_reg_write
     gen_log_predicated_reg_write_pair

now call gen_masked_reg_write, is there any reason why

     gen_log_reg_write_pair
     gen_log_predicated_reg_write

have been excluded?


>   static inline void gen_log_reg_write(int rnum, TCGv val)
>   {
> -    tcg_gen_mov_tl(hex_new_value[rnum], val);
> +    const hexagon_mut_entry entry = gpr_mut_masks[rnum];
> +    if (entry.present) {
> +        gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum],
> +            entry.mask);

Line up entry.mask); with rest of arguments.


> +    } else {
> +        tcg_gen_mov_tl(hex_new_value[rnum], val);
> +    }
>       if (HEX_DEBUG) {
>           /* Do this so HELPER(debug_commit_end) will know */
>           tcg_gen_movi_tl(hex_reg_written[rnum], 1);
> @@ -64,18 +80,32 @@ static inline void gen_log_reg_write(int rnum, TCGv val)
>   
>   static void gen_log_predicated_reg_write_pair(int rnum, TCGv_i64 val, int slot)
>   {
> +    const hexagon_mut_entry entry0 = gpr_mut_masks[rnum];
> +    const hexagon_mut_entry entry1 = gpr_mut_masks[rnum + 1];
>       TCGv val32 = tcg_temp_new();
>       TCGv zero = tcg_constant_tl(0);
>       TCGv slot_mask = tcg_temp_new();
> +    TCGv tmp_val = tcg_temp_new();
>   
>       tcg_gen_andi_tl(slot_mask, hex_slot_cancelled, 1 << slot);
> +
>       /* Low word */
>       tcg_gen_extrl_i64_i32(val32, val);
> +    if (entry0.present) {
> +        tcg_gen_mov_tl(tmp_val, val32);
> +        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry0.mask);
> +        tcg_temp_free(tmp_val);

There's a double free of tmp_val here. Even better would be to get rid of
tmp_val, and instead use

gen_masked_reg_write(hex_gpr[rnum], val32, val32, entry0.mask);


> +    }
>       tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum],
>                          slot_mask, zero,
>                          val32, hex_new_value[rnum]);
> +
>       /* High word */
>       tcg_gen_extrh_i64_i32(val32, val);
> +    if (entry1.present) {
> +        tcg_gen_mov_tl(tmp_val, val32);
> +        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry1.mask);

Same applies here, should be able to get rid of tmp_val, also shouldn't it
be hex_gpr[rnum+1] in the call to gen_masked_reg_write?


> +    }
>       tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum + 1],
>                          slot_mask, zero,
>                          val32, hex_new_value[rnum + 1]);
> @@ -95,6 +125,7 @@ static void gen_log_predicated_reg_write_pair(int rnum, TCGv_i64 val, int slot)
>   
>       tcg_temp_free(val32);
>       tcg_temp_free(slot_mask);
> +    tcg_temp_free(tmp_val);
>   }
>   
>   static void gen_log_reg_write_pair(int rnum, TCGv_i64 val)
> diff --git a/target/hexagon/hex_regs.h b/target/hexagon/hex_regs.h
> index a63c2c0fd5..db48cff96e 100644
> --- a/target/hexagon/hex_regs.h
> +++ b/target/hexagon/hex_regs.h
> @@ -79,6 +79,12 @@ enum {
>       HEX_REG_QEMU_HVX_CNT      = 54,
>       HEX_REG_UTIMERLO          = 62,
>       HEX_REG_UTIMERHI          = 63,
> +    HEX_REG_LAST_VALUE        = 64,
>   };
>   
> +
> +typedef struct {
> +    bool present;
> +    target_ulong mask;
> +} hexagon_mut_entry;

struct names should be CamelCase.


>   #endif
> diff --git a/target/hexagon/meson.build b/target/hexagon/meson.build
> index b61243103f..ea1f66982a 100644
> --- a/target/hexagon/meson.build
> +++ b/target/hexagon/meson.build
> @@ -168,6 +168,7 @@ hexagon_ss.add(files(
>       'op_helper.c',
>       'gdbstub.c',
>       'genptr.c',
> +    'gen_masked.c',
>       'reg_fields.c',
>       'decode.c',
>       'iclass.c',
> diff --git a/tests/tcg/hexagon/Makefile.target b/tests/tcg/hexagon/Makefile.target
> index 96a4d7a614..385d787a00 100644
> --- a/tests/tcg/hexagon/Makefile.target
> +++ b/tests/tcg/hexagon/Makefile.target
> @@ -43,6 +43,7 @@ HEX_TESTS += load_align
>   HEX_TESTS += atomics
>   HEX_TESTS += fpstuff
>   HEX_TESTS += overflow
> +HEX_TESTS += reg_mut
>   
>   TESTS += $(HEX_TESTS)
>   
> diff --git a/tests/tcg/hexagon/reg_mut.c b/tests/tcg/hexagon/reg_mut.c
> new file mode 100644
> index 0000000000..7e81ec6bf3
> --- /dev/null
> +++ b/tests/tcg/hexagon/reg_mut.c
> @@ -0,0 +1,107 @@
> +/*
> + *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
> + *
> + *  This program is free software; you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation; either version 2 of the License, or
> + *  (at your option) any later version.
> + *
> + *  This program is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <stdio.h>
> +#include <stdint.h>
> +
> +int err;
> +
> +#define check_ne(N, EXPECT) \
> +    { uint32_t value = N; \
> +        if (value == EXPECT) { \
> +            printf("ERROR: \"%s\" 0x%04x == 0x%04x at %s:%d\n", #N, value, \
> +                EXPECT, __FILE__, __LINE__); \
> +            err++; \
> +        } \
> +    }
> +
> +#define check(N, EXPECT) \
> +    { uint32_t value = N; \
> +        if (value != EXPECT) { \
> +            printf("ERROR: \"%s\" 0x%04x != 0x%04x at %s:%d\n", #N, value, \
> +                  EXPECT, __FILE__, __LINE__); \
> +            err++; \
> +        } \
> +    }
> +

Wrap these two macros in do {...} while(0) instead


> +#define READ_REG(reg_name, out_reg) \
> +  asm volatile ("%0 = " reg_name "\n\t" \
> +                : "=r"(out_reg) \
> +                : \
> +                : \
> +                ); \
> +
> +#define WRITE_REG(reg_name, out_reg, in_reg) \
> +  asm volatile (reg_name " = %1\n\t" \
> +                "%0 = " reg_name "\n\t" \
> +                : "=r"(out_reg) \
> +                : "r"(in_reg) \
> +                : reg_name \
> +                ); \

3 minor nitpicks, use 4-space indents for asm volatile lines, remove the
trailing ; \ at the end of the macros, and READ_REG is unused.


> +
> +   /*
> +    * Instruction word: { pc = r0 }
> +    *
> +    * This instruction is barred by the assembler.
> +    *
> +    *    3                   2                   1
> +    *  1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
> +    * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +    * |    Opc[A2_tfrrcr]   | Src[R0] |P P|                 |  C9/PC  |
> +    * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +    */

Very nice ascii art!


> +#define PC_EQ_R0 ".word 0x6220c009\n\t"
> +
> +static inline uint32_t set_pc(uint32_t in_reg)
> +{
> +    uint32_t out_reg;
> +    asm volatile("r0 = %1\n\t"
> +                 PC_EQ_R0
> +                 "%0 = pc\n\t"
> +                : "=r"(out_reg)
> +                : "r"(in_reg)
> +                : "r0");
> +    return out_reg;
> +}
> +
> +static inline uint32_t set_usr(uint32_t in_reg)
> +{
> +    uint32_t out_reg;
> +    WRITE_REG("usr", out_reg, in_reg);
> +    return out_reg;
> +}
> +
> +int main()
> +{
> +    check(set_usr(0x00),       0x00);
> +    check(set_usr(0xffffffff), 0x3ecfff3f);
> +    check(set_usr(0x00),       0x00);
> +    check(set_usr(0x01),       0x01);
> +    check(set_usr(0xff),       0x3f);
> +
> +    /*
> +     * PC is special.  Setting it to these values
> +     * should cause an instruction fetch miss.
> +     */
> +    check_ne(set_pc(0x00000000), 0x00000000);
> +    check_ne(set_pc(0xffffffff), 0xffffffff);
> +    check_ne(set_pc(0x00000001), 0x00000001);
> +    check_ne(set_pc(0x000000ff), 0x000000ff);
> +
> +    puts(err ? "FAIL" : "PASS");
> +    return err;
> +}

-- 
Anton Johansson,
rev.ng Labs Srl.

Re: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Richard Henderson]

On 9/1/22 22:29, Brian Cain wrote:
> +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
> +    target_ulong reg_mask) {
> +    TCGv set_bits = tcg_temp_new();
> +    TCGv cleared_bits = tcg_temp_new();
> +
> +    /*
> +     * set_bits = in_val & reg_mask
> +     * cleared_bits = (~in_val) & reg_mask
> +     */
> +    tcg_gen_andi_tl(set_bits, in_val, reg_mask);
> +    tcg_gen_not_tl(cleared_bits, in_val);
> +    tcg_gen_andi_tl(cleared_bits, cleared_bits, reg_mask);
> +
> +    /*
> +     * result = (reg_cur | set_bits) & (~cleared_bits)
> +     */
> +    tcg_gen_not_tl(cleared_bits, cleared_bits);
> +    tcg_gen_or_tl(set_bits, set_bits, cur_val);
> +    tcg_gen_and_tl(out_val, set_bits, cleared_bits);

This is overly complicated.  It should be

     out = (in & mask) | (cur & ~mask)

which is only 3 operations instead of 6:

     tcg_gen_andi_tl(t1, in_val, reg_mask);
     tcg_gen_andi_tl(t2, cur_val, ~reg_mask);
     tcg_gen_or_tl(out_val, t1, t2);


I'm surprised about new files for this simple operation.  Surely a subroutine within 
genptr.c would be sufficient.


> +static const hexagon_mut_entry gpr_mut_masks[HEX_REG_LAST_VALUE] = {
> +    [HEX_REG_PC] = {true, 0x00000000},
> +    [HEX_REG_GP] = {true, 0xffffffc0},
> +    [HEX_REG_USR] = {true, 0x3ecfff3f},
> +    [HEX_REG_UTIMERLO] = {true, 0x00000000},
> +    [HEX_REG_UTIMERHI] = {true, 0x00000000},
> +};
...
>   static inline void gen_log_reg_write(int rnum, TCGv val)
>   {
> -    tcg_gen_mov_tl(hex_new_value[rnum], val);
> +    const hexagon_mut_entry entry = gpr_mut_masks[rnum];
> +    if (entry.present) {
> +        gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum],
> +            entry.mask);
> +    } else {
> +        tcg_gen_mov_tl(hex_new_value[rnum], val);
> +    }

You could avoid the structure and .present flag by initializing all other entries to 
UINT32_MAX.  E.g.

static const target_ulong gpr_mut_masks[HEX_REG_LAST_VALUE] = {
     [0 ... HEX_REG_LAST_VALUE - 1] = UINT32_MAX,
     [HEX_REG_PC] = 0
     ...
};

It might be clearer, and easier to initialize, if you invert the sense of the mask: only 
set bits that are immutable, so that you get

static const target_ulong gpr_immutable_masks[HEX_REG_LAST_VALUE] = {
     [HEX_REG_PC] = UINT32_MAX,
     [HEX_REG_GP] = 0x3f,
     ...
};


r~

RE: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Brian Cain]

> -----Original Message-----
> From: Richard Henderson <richard.henderson@linaro.org>
...
> It might be clearer, and easier to initialize, if you invert the sense of the mask:

Ok -- thanks for the suggestions!  I'll give 'em all a try.

-Brian

RE: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Taylor Simpson]

> -----Original Message-----
> From: Brian Cain <bcain@quicinc.com>
> Sent: Thursday, September 1, 2022 4:30 PM
> To: qemu-devel@nongnu.org; Taylor Simpson <tsimpson@quicinc.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>; Brian Cain
> <bcain@quicinc.com>
> Subject: [PATCH] Hexagon (target/hexagon) implement mutability mask for
> GPRs
> 
> Some registers are defined to have immutable bits, this commit will
> implement that behavior.
> 
> Signed-off-by: Brian Cain <bcain@quicinc.com>
> ---
>  target/hexagon/gen_masked.c       |  44 ++++++++++++
>  target/hexagon/gen_masked.h       |  26 ++++++++
>  target/hexagon/genptr.c           |  33 ++++++++-
>  target/hexagon/hex_regs.h         |   6 ++
>  target/hexagon/meson.build        |   1 +
>  tests/tcg/hexagon/Makefile.target |   1 +
>  tests/tcg/hexagon/reg_mut.c       | 107
> ++++++++++++++++++++++++++++++
>  7 files changed, 217 insertions(+), 1 deletion(-)  create mode 100644
> target/hexagon/gen_masked.c  create mode 100644
> target/hexagon/gen_masked.h  create mode 100644
> tests/tcg/hexagon/reg_mut.c
> 
> diff --git a/target/hexagon/gen_masked.c b/target/hexagon/gen_masked.c
> new file mode 100644 index 0000000000..faffee2e13

Run
    git config diff.orderFile scripts/git.orderFile
in your workspace.

This will ensure (among other things) that the .h files appear in the patch before the .c files.  This makes it easier for the reviewers.


> --- /dev/null
> +++ b/target/hexagon/gen_masked.c
> @@ -0,0 +1,44 @@
> +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
> +    target_ulong reg_mask) {
> +    TCGv set_bits = tcg_temp_new();
> +    TCGv cleared_bits = tcg_temp_new();
> +
> +    /*
> +     * set_bits = in_val & reg_mask
> +     * cleared_bits = (~in_val) & reg_mask
> +     */
> +    tcg_gen_andi_tl(set_bits, in_val, reg_mask);
> +    tcg_gen_not_tl(cleared_bits, in_val);
> +    tcg_gen_andi_tl(cleared_bits, cleared_bits, reg_mask);
> +
> +    /*
> +     * result = (reg_cur | set_bits) & (~cleared_bits)
> +     */
> +    tcg_gen_not_tl(cleared_bits, cleared_bits);
> +    tcg_gen_or_tl(set_bits, set_bits, cur_val);
> +    tcg_gen_and_tl(out_val, set_bits, cleared_bits);
> +
> +    tcg_temp_free(set_bits);
> +    tcg_temp_free(cleared_bits);
> +}

In addition to Richard's feedback, you should do nothing when reg_mask is zero.


> diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c index
> 8a334ba07b..21385f556e 100644
> --- a/target/hexagon/genptr.c
> +++ b/target/hexagon/genptr.c
>  static inline void gen_log_reg_write(int rnum, TCGv val)  {
> -    tcg_gen_mov_tl(hex_new_value[rnum], val);
> +    const hexagon_mut_entry entry = gpr_mut_masks[rnum];
> +    if (entry.present) {
> +        gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum],

You can't write to hex_gpr here.  You have to wait to make sure the packet will commit.  Put this result back into val and do the mov to hex_new_value unconditionally.

> +            entry.mask);
> +    } else {
> +        tcg_gen_mov_tl(hex_new_value[rnum], val);
> +    }


>  static void gen_log_predicated_reg_write_pair(int rnum, TCGv_i64 val, int
> slot)  {
> +    const hexagon_mut_entry entry0 = gpr_mut_masks[rnum];
> +    const hexagon_mut_entry entry1 = gpr_mut_masks[rnum + 1];
>      TCGv val32 = tcg_temp_new();
>      TCGv zero = tcg_constant_tl(0);
>      TCGv slot_mask = tcg_temp_new();
> +    TCGv tmp_val = tcg_temp_new();
> 
>      tcg_gen_andi_tl(slot_mask, hex_slot_cancelled, 1 << slot);
> +
>      /* Low word */
>      tcg_gen_extrl_i64_i32(val32, val);
> +    if (entry0.present) {
> +        tcg_gen_mov_tl(tmp_val, val32);
> +        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry0.mask);

See previous comment.  Put the result back into val32 and let the subsequent code put it into hex_new_value if the slot isn't cancelled.

> +        tcg_temp_free(tmp_val);
> +    }
>      tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum],
>                         slot_mask, zero,
>                         val32, hex_new_value[rnum]);
> +
>      /* High word */
>      tcg_gen_extrh_i64_i32(val32, val);
> +    if (entry1.present) {
> +        tcg_gen_mov_tl(tmp_val, val32);
> +        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry1.mask);

Ditto.

> +    }


> a/target/hexagon/hex_regs.h b/target/hexagon/hex_regs.h index
> a63c2c0fd5..db48cff96e 100644
> --- a/target/hexagon/hex_regs.h
> +++ b/target/hexagon/hex_regs.h
> @@ -79,6 +79,12 @@ enum {
>      HEX_REG_QEMU_HVX_CNT      = 54,
>      HEX_REG_UTIMERLO          = 62,
>      HEX_REG_UTIMERHI          = 63,
> +    HEX_REG_LAST_VALUE        = 64,

You can use TOTAL_PER_THREAD_REGS (defined in cpu.h).

>  };


> diff --git a/tests/tcg/hexagon/reg_mut.c b/tests/tcg/hexagon/reg_mut.c
> new file mode 100644 index 0000000000..7e81ec6bf3
> --- /dev/null
> +++ b/tests/tcg/hexagon/reg_mut.c
> @@ -0,0 +1,107 @@
> +#define READ_REG(reg_name, out_reg) \
> +  asm volatile ("%0 = " reg_name "\n\t" \
> +                : "=r"(out_reg) \
> +                : \
> +                : \
> +                ); \
> +

Remove this - it isn't used.

> +int main()
> +{
> +    check(set_usr(0x00),       0x00);
> +    check(set_usr(0xffffffff), 0x3ecfff3f);
> +    check(set_usr(0x00),       0x00);
> +    check(set_usr(0x01),       0x01);
> +    check(set_usr(0xff),       0x3f);
> +
> +    /*
> +     * PC is special.  Setting it to these values
> +     * should cause an instruction fetch miss.

Why would there be an instruction fetch miss?  The gpr_mut_masks[HEX_REG_PC] is zero, so this instruction won't change PC.

> +     */
> +    check_ne(set_pc(0x00000000), 0x00000000);
> +    check_ne(set_pc(0xffffffff), 0xffffffff);
> +    check_ne(set_pc(0x00000001), 0x00000001);
> +    check_ne(set_pc(0x000000ff), 0x000000ff);
> +
> +    puts(err ? "FAIL" : "PASS");
> +    return err;
> +}

Add some tests that do the assignment inside a packet and using a register pair assignment.

Thanks,
Taylor

Re: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Richard Henderson]

On 9/6/22 23:26, Taylor Simpson wrote:
>> diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c index
>> 8a334ba07b..21385f556e 100644
>> --- a/target/hexagon/genptr.c
>> +++ b/target/hexagon/genptr.c
>>   static inline void gen_log_reg_write(int rnum, TCGv val)  {
>> -    tcg_gen_mov_tl(hex_new_value[rnum], val);
>> +    const hexagon_mut_entry entry = gpr_mut_masks[rnum];
>> +    if (entry.present) {
>> +        gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum],
> 
> You can't write to hex_gpr here.  You have to wait to make sure the packet will commit.  Put this result back into val and do the mov to hex_new_value unconditionally.

The feedback, then, is that the operands are confusingly ordered -- the output is to 
hex_new_value.  Brian, tcg functions generally list outputs first.


r~

RE: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs

[Brian Cain]

> -----Original Message-----
> From: Qemu-devel <qemu-devel-bounces+bcain=quicinc.com@nongnu.org>
> On Behalf Of Anton Johansson via
...
> Hi, Brian!
> 
> I've taken a look and most of this patch seems good, however I have a few
> comments/observations.

Anton, sorry I missed this message last week, only following up now.

> > Some registers are defined to have immutable bits, this commit
> > will implement that behavior.
> >
> > Signed-off-by: Brian Cain <bcain@quicinc.com>
> > ---
> >   target/hexagon/gen_masked.c       |  44 ++++++++++++
> >   target/hexagon/gen_masked.h       |  26 ++++++++
> >   target/hexagon/genptr.c           |  33 ++++++++-
> >   target/hexagon/hex_regs.h         |   6 ++
> >   target/hexagon/meson.build        |   1 +
> >   tests/tcg/hexagon/Makefile.target |   1 +
> >   tests/tcg/hexagon/reg_mut.c       | 107
> ++++++++++++++++++++++++++++++
> >   7 files changed, 217 insertions(+), 1 deletion(-)
> >   create mode 100644 target/hexagon/gen_masked.c
> >   create mode 100644 target/hexagon/gen_masked.h
> >   create mode 100644 tests/tcg/hexagon/reg_mut.c
> >
> > diff --git a/target/hexagon/gen_masked.c b/target/hexagon/gen_masked.c
> > new file mode 100644
> > index 0000000000..faffee2e13
> > --- /dev/null
> > +++ b/target/hexagon/gen_masked.c
> > @@ -0,0 +1,44 @@
> > +/*
> > + *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
> > + *
> > + *  This program is free software; you can redistribute it and/or modify
> > + *  it under the terms of the GNU General Public License as published by
> > + *  the Free Software Foundation; either version 2 of the License, or
> > + *  (at your option) any later version.
> > + *
> > + *  This program is distributed in the hope that it will be useful,
> > + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + *  GNU General Public License for more details.
> > + *
> > + *  You should have received a copy of the GNU General Public License
> > + *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> > + */
> > +
> > +#include "qemu/osdep.h"
> > +#include "tcg/tcg-op.h"
> > +#include "gen_masked.h"
> > +
> > +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
> > +    target_ulong reg_mask) {
> 
> Brace on new line per coding standard. Also I would line up the
> indentation with

Hmm - odd, I could have sworn checkpatch gave this a green light.  ☹  I will fix it.

> the rest of the arguments to match the rest of the hexagon frontend. I would
> suggest putting output arguments first to match other TCG ops, could become
> confusing otherwise, so
> 
>      void gen_masked_reg_write(TCGv out_val, TCGv in_val, TCGv cur_val,
>                                target_ulong reg_mask)
>      {
> 
> > +    TCGv set_bits = tcg_temp_new();
> > +    TCGv cleared_bits = tcg_temp_new();
> > +
> > +    /*
> > +     * set_bits = in_val & reg_mask
> > +     * cleared_bits = (~in_val) & reg_mask
> > +     */
> > +    tcg_gen_andi_tl(set_bits, in_val, reg_mask);
> > +    tcg_gen_not_tl(cleared_bits, in_val);
> > +    tcg_gen_andi_tl(cleared_bits, cleared_bits, reg_mask);
> > +
> > +    /*
> > +     * result = (reg_cur | set_bits) & (~cleared_bits)
> > +     */
> > +    tcg_gen_not_tl(cleared_bits, cleared_bits);
> > +    tcg_gen_or_tl(set_bits, set_bits, cur_val);
> > +    tcg_gen_and_tl(out_val, set_bits, cleared_bits);
> > +
> > +    tcg_temp_free(set_bits);
> > +    tcg_temp_free(cleared_bits);
> > +}
> 
> You could cut down on a single not operation in this function since
> 
>      ~cleared_bits = ~((~in_val) & reg_mask)
>                    = in_val | (~reg_mask)
> 
> I looked at the output of qemu-hexagon -d op_opt and this operation
> is not performed by the TCG optimizer, so we would end up saving
> an instruction.

IIUC Richard's suggestion reduces it yet further, so I'll use that algorithm instead.

> > diff --git a/target/hexagon/gen_masked.h b/target/hexagon/gen_masked.h
> > new file mode 100644
> > index 0000000000..71f4b2818b
> > --- /dev/null
> > +++ b/target/hexagon/gen_masked.h
> > @@ -0,0 +1,26 @@
> > +/*
> > + *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
> > + *
> > + *  This program is free software; you can redistribute it and/or modify
> > + *  it under the terms of the GNU General Public License as published by
> > + *  the Free Software Foundation; either version 2 of the License, or
> > + *  (at your option) any later version.
> > + *
> > + *  This program is distributed in the hope that it will be useful,
> > + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + *  GNU General Public License for more details.
> > + *
> > + *  You should have received a copy of the GNU General Public License
> > + *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> > + */
> > +
> > +#ifndef GEN_MASKED_H
> > +#define GEN_MASKED_H
> > +
> > +#include "tcg/tcg-op.h"
> > +
> > +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val,
> > +    target_ulong reg_mask);
> > +
> > +#endif /* GEN_MASKED_H */
> > diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c
> > index 8a334ba07b..21385f556e 100644
> > --- a/target/hexagon/genptr.c
> > +++ b/target/hexagon/genptr.c
> > @@ -29,6 +29,7 @@
> >   #undef QEMU_GENERATE
> >   #include "gen_tcg.h"
> >   #include "gen_tcg_hvx.h"
> > +#include "gen_masked.h"
> >
> >   static inline void gen_log_predicated_reg_write(int rnum, TCGv val, int slot)
> >   {
> > @@ -53,9 +54,24 @@ static inline void gen_log_predicated_reg_write(int
> rnum, TCGv val, int slot)
> >       tcg_temp_free(slot_mask);
> >   }
> >
> > +static const hexagon_mut_entry gpr_mut_masks[HEX_REG_LAST_VALUE] =
> {
> > +    [HEX_REG_PC] = {true, 0x00000000},
> > +    [HEX_REG_GP] = {true, 0xffffffc0},
> > +    [HEX_REG_USR] = {true, 0x3ecfff3f},
> > +    [HEX_REG_UTIMERLO] = {true, 0x00000000},
> > +    [HEX_REG_UTIMERHI] = {true, 0x00000000},
> > +};
> > +
> > +
> 
> Remove extra newline.
> 
> Also I notice
> 
>      gen_log_reg_write
>      gen_log_predicated_reg_write_pair
> 
> now call gen_masked_reg_write, is there any reason why
> 
>      gen_log_reg_write_pair
>      gen_log_predicated_reg_write
> 
> have been excluded?

Urk - that seems like an error.  I will look closer and probably end up including it in both of those.

> >   static inline void gen_log_reg_write(int rnum, TCGv val)
> >   {
> > -    tcg_gen_mov_tl(hex_new_value[rnum], val);
> > +    const hexagon_mut_entry entry = gpr_mut_masks[rnum];
> > +    if (entry.present) {
> > +        gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum],
> > +            entry.mask);
> 
> Line up entry.mask); with rest of arguments.

Richard's suggestion to remove the structure will obsolete this alignment issue.

> > +    } else {
> > +        tcg_gen_mov_tl(hex_new_value[rnum], val);
> > +    }
> >       if (HEX_DEBUG) {
> >           /* Do this so HELPER(debug_commit_end) will know */
> >           tcg_gen_movi_tl(hex_reg_written[rnum], 1);
> > @@ -64,18 +80,32 @@ static inline void gen_log_reg_write(int rnum, TCGv
> val)
> >
> >   static void gen_log_predicated_reg_write_pair(int rnum, TCGv_i64 val, int
> slot)
> >   {
> > +    const hexagon_mut_entry entry0 = gpr_mut_masks[rnum];
> > +    const hexagon_mut_entry entry1 = gpr_mut_masks[rnum + 1];
> >       TCGv val32 = tcg_temp_new();
> >       TCGv zero = tcg_constant_tl(0);
> >       TCGv slot_mask = tcg_temp_new();
> > +    TCGv tmp_val = tcg_temp_new();
> >
> >       tcg_gen_andi_tl(slot_mask, hex_slot_cancelled, 1 << slot);
> > +
> >       /* Low word */
> >       tcg_gen_extrl_i64_i32(val32, val);
> > +    if (entry0.present) {
> > +        tcg_gen_mov_tl(tmp_val, val32);
> > +        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry0.mask);
> > +        tcg_temp_free(tmp_val);
> 
> There's a double free of tmp_val here. Even better would be to get rid of
> tmp_val, and instead use
> 
> gen_masked_reg_write(hex_gpr[rnum], val32, val32, entry0.mask);
> 
> 
> > +    }
> >       tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum],
> >                          slot_mask, zero,
> >                          val32, hex_new_value[rnum]);
> > +
> >       /* High word */
> >       tcg_gen_extrh_i64_i32(val32, val);
> > +    if (entry1.present) {
> > +        tcg_gen_mov_tl(tmp_val, val32);
> > +        gen_masked_reg_write(hex_gpr[rnum], tmp_val, val32, entry1.mask);
> 
> Same applies here, should be able to get rid of tmp_val, also shouldn't it
> be hex_gpr[rnum+1] in the call to gen_masked_reg_write?

Hmm - good catch.  Underscores the need for regpair test cases, like Taylor's suggestion.

> > +    }
> >       tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum + 1],
> >                          slot_mask, zero,
> >                          val32, hex_new_value[rnum + 1]);
> > @@ -95,6 +125,7 @@ static void gen_log_predicated_reg_write_pair(int
> rnum, TCGv_i64 val, int slot)
> >
> >       tcg_temp_free(val32);
> >       tcg_temp_free(slot_mask);
> > +    tcg_temp_free(tmp_val);
> >   }
> >
> >   static void gen_log_reg_write_pair(int rnum, TCGv_i64 val)
> > diff --git a/target/hexagon/hex_regs.h b/target/hexagon/hex_regs.h
> > index a63c2c0fd5..db48cff96e 100644
> > --- a/target/hexagon/hex_regs.h
> > +++ b/target/hexagon/hex_regs.h
> > @@ -79,6 +79,12 @@ enum {
> >       HEX_REG_QEMU_HVX_CNT      = 54,
> >       HEX_REG_UTIMERLO          = 62,
> >       HEX_REG_UTIMERHI          = 63,
> > +    HEX_REG_LAST_VALUE        = 64,
> >   };
> >
> > +
> > +typedef struct {
> > +    bool present;
> > +    target_ulong mask;
> > +} hexagon_mut_entry;
> 
> struct names should be CamelCase.
> 
> 
> >   #endif
> > diff --git a/target/hexagon/meson.build b/target/hexagon/meson.build
> > index b61243103f..ea1f66982a 100644
> > --- a/target/hexagon/meson.build
> > +++ b/target/hexagon/meson.build
> > @@ -168,6 +168,7 @@ hexagon_ss.add(files(
> >       'op_helper.c',
> >       'gdbstub.c',
> >       'genptr.c',
> > +    'gen_masked.c',
> >       'reg_fields.c',
> >       'decode.c',
> >       'iclass.c',
> > diff --git a/tests/tcg/hexagon/Makefile.target
> b/tests/tcg/hexagon/Makefile.target
> > index 96a4d7a614..385d787a00 100644
> > --- a/tests/tcg/hexagon/Makefile.target
> > +++ b/tests/tcg/hexagon/Makefile.target
> > @@ -43,6 +43,7 @@ HEX_TESTS += load_align
> >   HEX_TESTS += atomics
> >   HEX_TESTS += fpstuff
> >   HEX_TESTS += overflow
> > +HEX_TESTS += reg_mut
> >
> >   TESTS += $(HEX_TESTS)
> >
> > diff --git a/tests/tcg/hexagon/reg_mut.c b/tests/tcg/hexagon/reg_mut.c
> > new file mode 100644
> > index 0000000000..7e81ec6bf3
> > --- /dev/null
> > +++ b/tests/tcg/hexagon/reg_mut.c
> > @@ -0,0 +1,107 @@
> > +/*
> > + *  Copyright(c) 2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
> > + *
> > + *  This program is free software; you can redistribute it and/or modify
> > + *  it under the terms of the GNU General Public License as published by
> > + *  the Free Software Foundation; either version 2 of the License, or
> > + *  (at your option) any later version.
> > + *
> > + *  This program is distributed in the hope that it will be useful,
> > + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + *  GNU General Public License for more details.
> > + *
> > + *  You should have received a copy of the GNU General Public License
> > + *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> > + */
> > +
> > +#include <stdio.h>
> > +#include <stdint.h>
> > +
> > +int err;
> > +
> > +#define check_ne(N, EXPECT) \
> > +    { uint32_t value = N; \
> > +        if (value == EXPECT) { \
> > +            printf("ERROR: \"%s\" 0x%04x == 0x%04x at %s:%d\n", #N, value, \
> > +                EXPECT, __FILE__, __LINE__); \
> > +            err++; \
> > +        } \
> > +    }
> > +
> > +#define check(N, EXPECT) \
> > +    { uint32_t value = N; \
> > +        if (value != EXPECT) { \
> > +            printf("ERROR: \"%s\" 0x%04x != 0x%04x at %s:%d\n", #N, value, \
> > +                  EXPECT, __FILE__, __LINE__); \
> > +            err++; \
> > +        } \
> > +    }
> > +
> 
> Wrap these two macros in do {...} while(0) instead
> 
> 
> > +#define READ_REG(reg_name, out_reg) \
> > +  asm volatile ("%0 = " reg_name "\n\t" \
> > +                : "=r"(out_reg) \
> > +                : \
> > +                : \
> > +                ); \
> > +
> > +#define WRITE_REG(reg_name, out_reg, in_reg) \
> > +  asm volatile (reg_name " = %1\n\t" \
> > +                "%0 = " reg_name "\n\t" \
> > +                : "=r"(out_reg) \
> > +                : "r"(in_reg) \
> > +                : reg_name \
> > +                ); \
> 
> 3 minor nitpicks, use 4-space indents for asm volatile lines, remove the
> trailing ; \ at the end of the macros, and READ_REG is unused.

Ok: I will fix these.

> 
> > +
> > +   /*
> > +    * Instruction word: { pc = r0 }
> > +    *
> > +    * This instruction is barred by the assembler.
> > +    *
> > +    *    3                   2                   1
> > +    *  1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
> > +    * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > +    * |    Opc[A2_tfrrcr]   | Src[R0] |P P|                 |  C9/PC  |
> > +    * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > +    */
> 
> Very nice ascii art!
> 
> 
> > +#define PC_EQ_R0 ".word 0x6220c009\n\t"
> > +
> > +static inline uint32_t set_pc(uint32_t in_reg)
> > +{
> > +    uint32_t out_reg;
> > +    asm volatile("r0 = %1\n\t"
> > +                 PC_EQ_R0
> > +                 "%0 = pc\n\t"
> > +                : "=r"(out_reg)
> > +                : "r"(in_reg)
> > +                : "r0");
> > +    return out_reg;
> > +}
> > +
> > +static inline uint32_t set_usr(uint32_t in_reg)
> > +{
> > +    uint32_t out_reg;
> > +    WRITE_REG("usr", out_reg, in_reg);
> > +    return out_reg;
> > +}
> > +
> > +int main()
> > +{
> > +    check(set_usr(0x00),       0x00);
> > +    check(set_usr(0xffffffff), 0x3ecfff3f);
> > +    check(set_usr(0x00),       0x00);
> > +    check(set_usr(0x01),       0x01);
> > +    check(set_usr(0xff),       0x3f);
> > +
> > +    /*
> > +     * PC is special.  Setting it to these values
> > +     * should cause an instruction fetch miss.
> > +     */
> > +    check_ne(set_pc(0x00000000), 0x00000000);
> > +    check_ne(set_pc(0xffffffff), 0xffffffff);
> > +    check_ne(set_pc(0x00000001), 0x00000001);
> > +    check_ne(set_pc(0x000000ff), 0x000000ff);
> > +
> > +    puts(err ? "FAIL" : "PASS");
> > +    return err;
> > +}
> 
> --
> Anton Johansson,
> rev.ng Labs Srl.
>