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Re: [PATCH v3 07/16] target/mips: Introduce decode tree bindings for MIP


From: Richard Henderson
Subject: Re: [PATCH v3 07/16] target/mips: Introduce decode tree bindings for MIPS16e ASE
Date: Tue, 26 Nov 2024 10:16:30 -0600
User-agent: Mozilla Thunderbird

On 11/26/24 07:59, Philippe Mathieu-Daudé wrote:
Introduce the MIPS16e decodetree configs for the 16-bit
and 32-bit instructions.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
  target/mips/tcg/translate.h             |  2 ++
  target/mips/tcg/mips16e_16.decode       |  9 +++++++++
  target/mips/tcg/mips16e_32.decode       |  9 +++++++++
  target/mips/tcg/mips16e_translate.c     | 14 ++++++++++++++
  target/mips/tcg/mips16e_translate.c.inc |  8 ++++++++
  target/mips/tcg/meson.build             |  3 +++
  6 files changed, 45 insertions(+)
  create mode 100644 target/mips/tcg/mips16e_16.decode
  create mode 100644 target/mips/tcg/mips16e_32.decode
  create mode 100644 target/mips/tcg/mips16e_translate.c

diff --git a/target/mips/tcg/translate.h b/target/mips/tcg/translate.h
index a65ab4a747c..d1aa811cfa1 100644
--- a/target/mips/tcg/translate.h
+++ b/target/mips/tcg/translate.h
@@ -223,6 +223,8 @@ bool decode_64bit_enabled(DisasContext *ctx);
/* decodetree generated */
  bool decode_isa_rel6(DisasContext *ctx, uint32_t insn);
+bool decode_ase_mips16e_16(DisasContext *ctx, uint16_t insn);
+bool decode_ase_mips16e_32(DisasContext *ctx, uint32_t insn);
  bool decode_ase_msa(DisasContext *ctx, uint32_t insn);
  bool decode_ext_txx9(DisasContext *ctx, uint32_t insn);
  bool decode_ext_loongson(DisasContext *ctx, uint32_t insn);
diff --git a/target/mips/tcg/mips16e_16.decode 
b/target/mips/tcg/mips16e_16.decode
new file mode 100644
index 00000000000..82586493f68
--- /dev/null
+++ b/target/mips/tcg/mips16e_16.decode
@@ -0,0 +1,9 @@
+# MIPS16e 16-bit instruction set extensions
+#
+# Copyright (C) 2021  Philippe Mathieu-Daudé
+#
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+# Reference: MIPS Architecture for Programmers, Volume IV-a
+#            The MIPS16e Application Specific Extension
+#            (Document Number: MD00076)
diff --git a/target/mips/tcg/mips16e_32.decode 
b/target/mips/tcg/mips16e_32.decode
new file mode 100644
index 00000000000..fc429049e18
--- /dev/null
+++ b/target/mips/tcg/mips16e_32.decode
@@ -0,0 +1,9 @@
+# MIPS16e 32-bit instruction set extensions
+#
+# Copyright (C) 2021  Philippe Mathieu-Daudé
+#
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+# Reference: MIPS Architecture for Programmers, Volume IV-a
+#            The MIPS16e Application Specific Extension
+#            (Document Number: MD00076)
diff --git a/target/mips/tcg/mips16e_translate.c 
b/target/mips/tcg/mips16e_translate.c
new file mode 100644
index 00000000000..6de9928b37e
--- /dev/null
+++ b/target/mips/tcg/mips16e_translate.c
@@ -0,0 +1,14 @@
+/*
+ * MIPS emulation for QEMU - MIPS16e translation routines
+ *
+ * Copyright (c) 2021 Philippe Mathieu-Daudé <f4bug@amsat.org>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "translate.h"
+
+/* Include the auto-generated decoders.  */
+#include "decode-mips16e_16.c.inc"
+#include "decode-mips16e_32.c.inc"
diff --git a/target/mips/tcg/mips16e_translate.c.inc 
b/target/mips/tcg/mips16e_translate.c.inc
index defef3ce559..a57ae4e95b1 100644
--- a/target/mips/tcg/mips16e_translate.c.inc
+++ b/target/mips/tcg/mips16e_translate.c.inc
@@ -657,6 +657,14 @@ static int decode_ase_mips16e(CPUMIPSState *env, 
DisasContext *ctx)
      int n_bytes;
ctx->opcode = translator_lduw(env, &ctx->base, ctx->base.pc_next);
+
+    if (decode_ase_mips16e_16(ctx, ctx->opcode)) {
+        return 2;
+    }
+    if (decode_ase_mips16e_32(ctx, ctx->opcode)) {
+        return 4;
+    }
This is misplaced wrt loading 32-bits of opcode.  You have two options:

    opcode = lduw(...)
    if (extract32(opcode, 11, 5) == M16_OPC_EXTEND) {
        opcode <<= 16;
        opcode |= lduw(...);
        decode_ase_mips16e_32(...);
    } else {
        decode_ase_mips16e_16(...);
    }

Or, make use of the variable-length support in decodetree. Given the trivial test above, the complexity and oddness of the variable-length stuff doesn't seem worth it.

r~



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