[PATCH 4/5] target/arm: Support more GM blocksizes

[Richard Henderson]

Support all of the easy GM block sizes.
Use direct memory operations, since the pointers are aligned.

While BS=2 (16 bytes, 1 tag) is a legal setting, that requires
an atomic store of one nibble.  This is not difficult, but there
is also no point in supporting it until required.

Note that cortex-a710 sets GM blocksize to match its cacheline
size of 64 bytes.  I expect many implementations will also
match the cacheline, which makes 16 bytes very unlikely.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/tcg/mte_helper.c | 61 ++++++++++++++++++++++++++++++++-----
 1 file changed, 53 insertions(+), 8 deletions(-)

diff --git a/target/arm/tcg/mte_helper.c b/target/arm/tcg/mte_helper.c
index 3640c6e57f..6faf4e42d5 100644
--- a/target/arm/tcg/mte_helper.c
+++ b/target/arm/tcg/mte_helper.c
@@ -428,6 +428,8 @@ uint64_t HELPER(ldgm)(CPUARMState *env, uint64_t ptr)
     int gm_bs = env_archcpu(env)->gm_blocksize;
     int gm_bs_bytes = 4 << gm_bs;
     void *tag_mem;
+    uint64_t ret;
+    int shift;
 
     ptr = QEMU_ALIGN_DOWN(ptr, gm_bs_bytes);
 
@@ -443,16 +445,39 @@ uint64_t HELPER(ldgm)(CPUARMState *env, uint64_t ptr)
 
     /*
      * The ordering of elements within the word corresponds to
-     * a little-endian operation.
+     * a little-endian operation.  Computation of shift comes from
+     *
+     *     index = address<LOG2_TAG_GRANULE+3:LOG2_TAG_GRANULE>
+     *     data<index*4+3:index*4> = tag
+     *
+     * Because of the alignment of ptr above, BS=6 has shift=0.
+     * All memory operations are aligned.
      */
     switch (gm_bs) {
-    case 6:
-        /* 256 bytes -> 16 tags -> 64 result bits */
-        return ldq_le_p(tag_mem);
-    default:
+    case 2:
         /* cpu configured with unsupported gm blocksize. */
         g_assert_not_reached();
+    case 3:
+        /* 32 bytes -> 2 tags -> 8 result bits */
+        ret = *(uint8_t *)tag_mem;
+        break;
+    case 4:
+        /* 64 bytes -> 4 tags -> 16 result bits */
+        ret = cpu_to_le16(*(uint16_t *)tag_mem);
+        break;
+    case 5:
+        /* 128 bytes -> 8 tags -> 32 result bits */
+        ret = cpu_to_le32(*(uint32_t *)tag_mem);
+        break;
+    case 6:
+        /* 256 bytes -> 16 tags -> 64 result bits */
+        return cpu_to_le64(*(uint64_t *)tag_mem);
+    default:
+        /* cpu configured with invalid gm blocksize. */
+        g_assert_not_reached();
     }
+    shift = extract64(ptr, LOG2_TAG_GRANULE, 4) * 4;
+    return ret << shift;
 }
 
 void HELPER(stgm)(CPUARMState *env, uint64_t ptr, uint64_t val)
@@ -462,6 +487,7 @@ void HELPER(stgm)(CPUARMState *env, uint64_t ptr, uint64_t 
val)
     int gm_bs = env_archcpu(env)->gm_blocksize;
     int gm_bs_bytes = 4 << gm_bs;
     void *tag_mem;
+    int shift;
 
     ptr = QEMU_ALIGN_DOWN(ptr, gm_bs_bytes);
 
@@ -480,14 +506,33 @@ void HELPER(stgm)(CPUARMState *env, uint64_t ptr, 
uint64_t val)
 
     /*
      * The ordering of elements within the word corresponds to
-     * a little-endian operation.
+     * a little-endian operation.  See LDGM for comments on shift.
+     * All memory operations are aligned.
      */
+    shift = extract64(ptr, LOG2_TAG_GRANULE, 4) * 4;
+    val >>= shift;
     switch (gm_bs) {
+    case 2:
+        /* cpu configured with unsupported gm blocksize. */
+        g_assert_not_reached();
+    case 3:
+        /* 32 bytes -> 2 tags -> 8 result bits */
+        *(uint8_t *)tag_mem = val;
+        break;
+    case 4:
+        /* 64 bytes -> 4 tags -> 16 result bits */
+        *(uint16_t *)tag_mem = cpu_to_le16(val);
+        break;
+    case 5:
+        /* 128 bytes -> 8 tags -> 32 result bits */
+        *(uint32_t *)tag_mem = cpu_to_le32(val);
+        break;
     case 6:
-        stq_le_p(tag_mem, val);
+        /* 256 bytes -> 16 tags -> 64 result bits */
+        *(uint64_t *)tag_mem = cpu_to_le64(val);
         break;
     default:
-        /* cpu configured with unsupported gm blocksize. */
+        /* cpu configured with invalid gm blocksize. */
         g_assert_not_reached();
     }
 }
-- 
2.34.1