jit: Add more foundational code

Strengthens the decoder's foundation but does not yet implement the core
instruction lookup table logic or the public arm32_decode API. These
will be addressed in future patches.

Signed-off-by: Ronald Caesar <github43132@proton.me>

src/jit/decoder/arm32.cpp

@@ -1,19 +1,134 @@
 #include "arm32.h"
+#include <string.h>
+#include "common/passert.h"
+
+#define LOG_MODULE "jit"
+#include "common/logging.h"
+
 namespace pound::jit::decoder
 {
+/* Increase value as more instructions get implemented */
+#define INSTRUCTION_ARRAY_CAPACITY 4
 arm32_decoder_t g_arm32_decoder = {};
 
-void arm32_add_instruction(arm32_decoder_t* decoder, const char* nane, arm32_opcode_t mask, arm32_opcode_t expected,
-                           arm32_handler_fn handler)
-{
-}
+/*
+ * ============================================================================
+ *                              Foward Declarations
+ * ============================================================================
+ */
+void arm32_add_instruction(arm32_decoder_t* decoder, const char* name, const char* bitstring, arm32_handler_fn handler);
+void arm32_ADD_imm_handler(arm32_decoder_t* decoder, arm32_instruction_t instruction);
 
-void arm32_ADD_imm_handler(arm32_decoder_t* decoder, arm32_instruction_t instruction) {}
+void arm32_parse_bitstring(const char* bitstring, uint32_t* mask, uint32_t* expected);
+void arm32_grow_instructions_array(arm32_decoder_t* decoder, size_t new_capacity);
 
-void arm32_init(arm32_decoder_t* decoder)
+/*
+ * ============================================================================
+ *                              Public Functions
+ * ============================================================================
+ */
+void arm32_init(pound::host::memory::arena_t allocator, arm32_decoder_t* decoder)
 {
-#define INST(fn, name, bitstring) arm32_add_instruction(decoder, name, 0, 0, &arm32_##fn##_handler);
+    PVM_ASSERT(nullptr != decoder);
+    PVM_ASSERT(nullptr != allocator.data);
+
+    (void)memset(decoder, 0, sizeof(arm32_decoder_t));
+    decoder->allocator = allocator;
+
+    /* Setup Instructions array.*/
+    size_t instructions_array_size = INSTRUCTION_ARRAY_CAPACITY * sizeof(arm32_instruction_info_t);
+    PVM_ASSERT(instructions_array_size <= decoder->allocator.capacity);
+    LOG_TRACE("Growing instructions array to %d bytes", instructions_array_size);
+
+    void* new_ptr = pound::host::memory::arena_allocate(&decoder->allocator, instructions_array_size);
+    PVM_ASSERT(nullptr != new_ptr);
+
+    decoder->instructions = (arm32_instruction_info_t*)new_ptr;
+    decoder->instruction_capacity = INSTRUCTION_ARRAY_CAPACITY;
+
+    /* Add all Arm32 instructions */
+#define INST(fn, name, bitstring) arm32_add_instruction(decoder, name, bitstring, &arm32_##fn##_handler);
 #include "./arm32.inc"
 #undef INST
 }
+
+void arm32_add_instruction(arm32_decoder_t* decoder, const char* name, const char* bitstring, arm32_handler_fn handler)
+{
+    PVM_ASSERT(nullptr != decoder);
+    PVM_ASSERT(nullptr != decoder->allocator.data);
+    PVM_ASSERT(nullptr != name);
+    PVM_ASSERT(nullptr != bitstring);
+    PVM_ASSERT(decoder->instruction_count < decoder->instruction_capacity);
+
+    LOG_TRACE("Adding '%s' instruction to lookup table.", name);
+    arm32_opcode_t mask = 0;
+    arm32_opcode_t expected = 0;
+    arm32_parse_bitstring(bitstring, &mask, &expected);
+
+    LOG_TRACE("Mask: %x", mask);
+    LOG_TRACE("Expected: %x", expected);
+
+    arm32_instruction_info_t* info = &decoder->instructions[decoder->instruction_count];
+    info->name = name;
+    info->mask = mask;
+    info->expected = expected;
+    info->handler = handler;
+
+    /* Calculate priority based on number of fixed bits. */
+    info->priority = 0;
+    for (int i = 0; i < 32; ++i)
+    {
+        if ((mask >> i) & 1)
+        {
+            ++info->priority;
+        }
+    }
+
+    ++decoder->instruction_count;
+
+    /* TODO(GloriousTacoo:jit): Add instruction to lookup table. */
+}
+void arm32_ADD_imm_handler(arm32_decoder_t* decoder, arm32_instruction_t instruction) {}
+
+/*
+ * ============================================================================
+ *                          Private Functions
+ * ============================================================================
+ */
+
+void arm32_parse_bitstring(const char* bitstring, uint32_t* mask, uint32_t* expected)
+{
+    PVM_ASSERT(nullptr != bitstring);
+    PVM_ASSERT(nullptr != mask);
+    PVM_ASSERT(nullptr != expected);
+    PVM_ASSERT(32 == strlen(bitstring));
+
+    *mask = 0;
+    *expected = 0;
+    uint8_t instruction_size_bits = 32;
+    for (int i = 0; (i < instruction_size_bits) && (bitstring[i] != '\0'); ++i)
+    {
+        uint32_t bit_position = 31 - i;
+        switch (bitstring[i])
+        {
+            case '0':
+                *mask |= (1U << bit_position);
+                break;
+            case '1':
+                *mask |= (1U << bit_position);
+                *expected |= (1U << bit_position);
+                break;
+            case 'c':
+            case 'n':
+            case 'd':
+            case 'r':
+            case 'v':
+            case 's':
+            case 'S':
+                break;
+            default:
+                PVM_ASSERT_MSG(false, "Invalid bitstring character: %c", bitstring[i]);
+        }
+    }
+}
 }  // namespace pound::jit::decoder