py: Add support for emitting native x86 machine code.

1 files changed, 520 insertions, 0 deletions

diff --git a/py/asmx86.c b/py/asmx86.c
new file mode 100644
index 000000000..a0a38161c
--- /dev/null
+++ b/py/asmx86.c
@@ -0,0 +1,520 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+
+#include "mpconfig.h"
+#include "misc.h"
+
+// wrapper around everything in this file
+#if MICROPY_EMIT_X86
+
+#include "asmx86.h"
+
+/* all offsets are measured in multiples of 4 bytes */
+#define WORD_SIZE                (4)
+
+#define OPCODE_NOP               (0x90)
+#define OPCODE_PUSH_R32          (0x50)
+//#define OPCODE_PUSH_I32          (0x68)
+//#define OPCODE_PUSH_M32          (0xff) /* /6 */
+#define OPCODE_POP_R32           (0x58)
+#define OPCODE_RET               (0xc3)
+//#define OPCODE_MOV_I8_TO_R8      (0xb0) /* +rb */
+#define OPCODE_MOV_I32_TO_R32    (0xb8)
+//#define OPCODE_MOV_I32_TO_RM32   (0xc7)
+#define OPCODE_MOV_R32_TO_RM32   (0x89)
+#define OPCODE_MOV_RM32_TO_R32   (0x8b)
+#define OPCODE_LEA_MEM_TO_R32    (0x8d) /* /r */
+#define OPCODE_XOR_R32_TO_RM32   (0x31) /* /r */
+#define OPCODE_ADD_R32_TO_RM32   (0x01)
+//#define OPCODE_ADD_I32_TO_RM32   (0x81) /* /0 */
+//#define OPCODE_ADD_I8_TO_RM32    (0x83) /* /0 */
+//#define OPCODE_SUB_R32_FROM_RM32 (0x29)
+#define OPCODE_SUB_I32_FROM_RM32 (0x81) /* /5 */
+#define OPCODE_SUB_I8_FROM_RM32  (0x83) /* /5 */
+//#define OPCODE_SHL_RM32_BY_I8    (0xc1) /* /4 */
+//#define OPCODE_SHR_RM32_BY_I8    (0xc1) /* /5 */
+//#define OPCODE_SAR_RM32_BY_I8    (0xc1) /* /7 */
+//#define OPCODE_CMP_I32_WITH_RM32 (0x81) /* /7 */
+//#define OPCODE_CMP_I8_WITH_RM32  (0x83) /* /7 */
+#define OPCODE_CMP_R32_WITH_RM32 (0x39)
+//#define OPCODE_CMP_RM32_WITH_R32 (0x3b)
+#define OPCODE_TEST_R8_WITH_RM8  (0x84) /* /r */
+#define OPCODE_JMP_REL8          (0xeb)
+#define OPCODE_JMP_REL32         (0xe9)
+#define OPCODE_JCC_REL8          (0x70) /* | jcc type */
+#define OPCODE_JCC_REL32_A       (0x0f)
+#define OPCODE_JCC_REL32_B       (0x80) /* | jcc type */
+#define OPCODE_SETCC_RM8_A       (0x0f)
+#define OPCODE_SETCC_RM8_B       (0x90) /* | jcc type, /0 */
+#define OPCODE_CALL_REL32        (0xe8)
+#define OPCODE_CALL_RM32         (0xff) /* /2 */
+#define OPCODE_LEAVE             (0xc9)
+
+#define MODRM_R32(x)    ((x) << 3)
+#define MODRM_RM_DISP0  (0x00)
+#define MODRM_RM_DISP8  (0x40)
+#define MODRM_RM_DISP32 (0x80)
+#define MODRM_RM_REG    (0xc0)
+#define MODRM_RM_R32(x) (x)
+
+#define IMM32_L0(x) ((x) & 0xff)
+#define IMM32_L1(x) (((x) >> 8) & 0xff)
+#define IMM32_L2(x) (((x) >> 16) & 0xff)
+#define IMM32_L3(x) (((x) >> 24) & 0xff)
+
+#define SIGNED_FIT8(x) (((x) & 0xffffff80) == 0) || (((x) & 0xffffff80) == 0xffffff80)
+
+struct _asm_x86_t {
+    uint pass;
+    mp_uint_t code_offset;
+    mp_uint_t code_size;
+    byte *code_base;
+    byte dummy_data[8];
+
+    uint max_num_labels;
+    int *label_offsets;
+    int num_locals;
+};
+
+asm_x86_t *asm_x86_new(mp_uint_t max_num_labels) {
+    asm_x86_t *as;
+
+    as = m_new0(asm_x86_t, 1);
+    as->max_num_labels = max_num_labels;
+    as->label_offsets = m_new(int, max_num_labels);
+
+    return as;
+}
+
+void asm_x86_free(asm_x86_t *as, bool free_code) {
+    if (free_code) {
+        MP_PLAT_FREE_EXEC(as->code_base, as->code_size);
+    }
+    m_del_obj(asm_x86_t, as);
+}
+
+void asm_x86_start_pass(asm_x86_t *as, mp_uint_t pass) {
+    as->pass = pass;
+    as->code_offset = 0;
+    if (pass == ASM_X86_PASS_COMPUTE) {
+        // reset all labels
+        memset(as->label_offsets, -1, as->max_num_labels * sizeof(int));
+    }
+}
+
+void asm_x86_end_pass(asm_x86_t *as) {
+    if (as->pass == ASM_X86_PASS_COMPUTE) {
+        MP_PLAT_ALLOC_EXEC(as->code_offset, (void**) &as->code_base, &as->code_size);
+        if(as->code_base == NULL) {
+            assert(0);
+        }
+    }
+}
+
+// all functions must go through this one to emit bytes
+STATIC byte *asm_x86_get_cur_to_write_bytes(asm_x86_t *as, int num_bytes_to_write) {
+    //printf("emit %d\n", num_bytes_to_write);
+    if (as->pass < ASM_X86_PASS_EMIT) {
+        as->code_offset += num_bytes_to_write;
+        return as->dummy_data;
+    } else {
+        assert(as->code_offset + num_bytes_to_write <= as->code_size);
+        byte *c = as->code_base + as->code_offset;
+        as->code_offset += num_bytes_to_write;
+        return c;
+    }
+}
+
+mp_uint_t asm_x86_get_code_size(asm_x86_t *as) {
+    return as->code_size;
+}
+
+void *asm_x86_get_code(asm_x86_t *as) {
+    return as->code_base;
+}
+
+STATIC void asm_x86_write_byte_1(asm_x86_t *as, byte b1) {
+    byte* c = asm_x86_get_cur_to_write_bytes(as, 1);
+    c[0] = b1;
+}
+
+STATIC void asm_x86_write_byte_2(asm_x86_t *as, byte b1, byte b2) {
+    byte* c = asm_x86_get_cur_to_write_bytes(as, 2);
+    c[0] = b1;
+    c[1] = b2;
+}
+
+STATIC void asm_x86_write_byte_3(asm_x86_t *as, byte b1, byte b2, byte b3) {
+    byte* c = asm_x86_get_cur_to_write_bytes(as, 3);
+    c[0] = b1;
+    c[1] = b2;
+    c[2] = b3;
+}
+
+STATIC void asm_x86_write_word32(asm_x86_t *as, int w32) {
+    byte* c = asm_x86_get_cur_to_write_bytes(as, 4);
+    c[0] = IMM32_L0(w32);
+    c[1] = IMM32_L1(w32);
+    c[2] = IMM32_L2(w32);
+    c[3] = IMM32_L3(w32);
+}
+
+STATIC void asm_x86_write_r32_disp(asm_x86_t *as, int r32, int disp_r32, int disp_offset) {
+    assert(disp_r32 != REG_ESP);
+
+    if (disp_offset == 0 && disp_r32 != REG_EBP) {
+        asm_x86_write_byte_1(as, MODRM_R32(r32) | MODRM_RM_DISP0 | MODRM_RM_R32(disp_r32));
+    } else if (SIGNED_FIT8(disp_offset)) {
+        asm_x86_write_byte_2(as, MODRM_R32(r32) | MODRM_RM_DISP8 | MODRM_RM_R32(disp_r32), IMM32_L0(disp_offset));
+    } else {
+        asm_x86_write_byte_1(as, MODRM_R32(r32) | MODRM_RM_DISP32 | MODRM_RM_R32(disp_r32));
+        asm_x86_write_word32(as, disp_offset);
+    }
+}
+
+STATIC void asm_x86_nop(asm_x86_t *as) {
+    asm_x86_write_byte_1(as, OPCODE_NOP);
+}
+
+STATIC void asm_x86_push_r32(asm_x86_t *as, int src_r32) {
+    asm_x86_write_byte_1(as, OPCODE_PUSH_R32 | src_r32);
+}
+
+#if 0
+void asm_x86_push_i32(asm_x86_t *as, int src_i32) {
+    asm_x86_write_byte_1(as, OPCODE_PUSH_I32);
+    asm_x86_write_word32(as, src_i32);
+}
+
+void asm_x86_push_disp(asm_x86_t *as, int src_r32, int src_offset) {
+    asm_x86_write_byte_1(as, OPCODE_PUSH_M32);
+    asm_x86_write_r32_disp(as, 6, src_r32, src_offset);
+}
+#endif
+
+STATIC void asm_x86_pop_r32(asm_x86_t *as, int dest_r32) {
+    asm_x86_write_byte_1(as, OPCODE_POP_R32 | dest_r32);
+}
+
+STATIC void asm_x86_ret(asm_x86_t *as) {
+    asm_x86_write_byte_1(as, OPCODE_RET);
+}
+
+void asm_x86_mov_r32_to_r32(asm_x86_t *as, int src_r32, int dest_r32) {
+    asm_x86_write_byte_2(as, OPCODE_MOV_R32_TO_RM32, MODRM_R32(src_r32) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+}
+
+STATIC void asm_x86_mov_r32_to_disp(asm_x86_t *as, int src_r32, int dest_r32, int dest_disp) {
+    asm_x86_write_byte_1(as, OPCODE_MOV_R32_TO_RM32);
+    asm_x86_write_r32_disp(as, src_r32, dest_r32, dest_disp);
+}
+
+STATIC void asm_x86_mov_disp_to_r32(asm_x86_t *as, int src_r32, int src_disp, int dest_r32) {
+    asm_x86_write_byte_1(as, OPCODE_MOV_RM32_TO_R32);
+    asm_x86_write_r32_disp(as, dest_r32, src_r32, src_disp);
+}
+
+STATIC void asm_x86_lea_disp_to_r32(asm_x86_t *as, int src_r32, int src_disp, int dest_r32) {
+    asm_x86_write_byte_1(as, OPCODE_LEA_MEM_TO_R32);
+    asm_x86_write_r32_disp(as, dest_r32, src_r32, src_disp);
+}
+
+#if 0
+void asm_x86_mov_i8_to_r8(asm_x86_t *as, int src_i8, int dest_r32) {
+    asm_x86_write_byte_2(as, OPCODE_MOV_I8_TO_R8 | dest_r32, src_i8);
+}
+#endif
+
+void asm_x86_mov_i32_to_r32(asm_x86_t *as, int src_i32, int dest_r32) {
+    asm_x86_write_byte_1(as, OPCODE_MOV_I32_TO_R32 | dest_r32);
+    asm_x86_write_word32(as, src_i32);
+}
+
+// src_i32 is stored as a full word in the code, and aligned to machine-word boundary
+void asm_x86_mov_i32_to_r32_aligned(asm_x86_t *as, int32_t src_i32, int dest_r32) {
+    // mov instruction uses 1 byte for the instruction, before the i32
+    while (((as->code_offset + 1) & (WORD_SIZE - 1)) != 0) {
+        asm_x86_nop(as);
+    }
+    asm_x86_mov_i32_to_r32(as, src_i32, dest_r32);
+}
+
+void asm_x86_xor_r32_to_r32(asm_x86_t *as, int src_r32, int dest_r32) {
+    asm_x86_write_byte_2(as, OPCODE_XOR_R32_TO_RM32, MODRM_R32(src_r32) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+}
+
+void asm_x86_add_r32_to_r32(asm_x86_t *as, int src_r32, int dest_r32) {
+    asm_x86_write_byte_2(as, OPCODE_ADD_R32_TO_RM32, MODRM_R32(src_r32) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+}
+
+#if 0
+void asm_x86_add_i32_to_r32(asm_x86_t *as, int src_i32, int dest_r32)
+{
+    if (SIGNED_FIT8(src_i32))
+    {
+        asm_x86_write_byte_2(as, OPCODE_ADD_I8_TO_RM32, MODRM_R32(0) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+        asm_x86_write_byte_1(as, src_i32 & 0xff);
+    }
+    else
+    {
+        asm_x86_write_byte_2(as, OPCODE_ADD_I32_TO_RM32, MODRM_R32(0) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+        asm_x86_write_word32(as, src_i32);
+    }
+}
+
+void asm_x86_sub_r32_from_r32(asm_x86_t *as, int src_r32, int dest_r32) {
+    asm_x86_write_byte_2(as, OPCODE_SUB_R32_FROM_RM32, MODRM_R32(src_r32) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+}
+#endif
+
+void asm_x86_sub_i32_from_r32(asm_x86_t *as, int src_i32, int dest_r32) {
+    if (SIGNED_FIT8(src_i32)) {
+        // defaults to 32 bit operation
+        asm_x86_write_byte_2(as, OPCODE_SUB_I8_FROM_RM32, MODRM_R32(5) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+        asm_x86_write_byte_1(as, src_i32 & 0xff);
+    } else {
+        // defaults to 32 bit operation
+        asm_x86_write_byte_2(as, OPCODE_SUB_I32_FROM_RM32, MODRM_R32(5) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
+        asm_x86_write_word32(as, src_i32);
+    }
+}
+
+#if 0
+/* shifts not tested */
+void asm_x86_shl_r32_by_imm(asm_x86_t *as, int r32, int imm) {
+    asm_x86_write_byte_2(as, OPCODE_SHL_RM32_BY_I8, MODRM_R32(4) | MODRM_RM_REG | MODRM_RM_R32(r32));
+    asm_x86_write_byte_1(as, imm);
+}
+
+void asm_x86_shr_r32_by_imm(asm_x86_t *as, int r32, int imm) {
+    asm_x86_write_byte_2(as, OPCODE_SHR_RM32_BY_I8, MODRM_R32(5) | MODRM_RM_REG | MODRM_RM_R32(r32));
+    asm_x86_write_byte_1(as, imm);
+}
+
+void asm_x86_sar_r32_by_imm(asm_x86_t *as, int r32, int imm) {
+    asm_x86_write_byte_2(as, OPCODE_SAR_RM32_BY_I8, MODRM_R32(7) | MODRM_RM_REG | MODRM_RM_R32(r32));
+    asm_x86_write_byte_1(as, imm);
+}
+#endif
+
+void asm_x86_cmp_r32_with_r32(asm_x86_t *as, int src_r32_a, int src_r32_b) {
+    asm_x86_write_byte_2(as, OPCODE_CMP_R32_WITH_RM32, MODRM_R32(src_r32_a) | MODRM_RM_REG | MODRM_RM_R32(src_r32_b));
+}
+
+#if 0
+void asm_x86_cmp_i32_with_r32(asm_x86_t *as, int src_i32, int src_r32) {
+    if (SIGNED_FIT8(src_i32)) {
+        asm_x86_write_byte_2(as, OPCODE_CMP_I8_WITH_RM32, MODRM_R32(7) | MODRM_RM_REG | MODRM_RM_R32(src_r32));
+        asm_x86_write_byte_1(as, src_i32 & 0xff);
+    } else {
+        asm_x86_write_byte_2(as, OPCODE_CMP_I32_WITH_RM32, MODRM_R32(7) | MODRM_RM_REG | MODRM_RM_R32(src_r32));
+        asm_x86_write_word32(as, src_i32);
+    }
+}
+#endif
+
+void asm_x86_test_r8_with_r8(asm_x86_t *as, int src_r32_a, int src_r32_b) {
+    // TODO implement for other registers
+    assert(src_r32_a == REG_EAX);
+    assert(src_r32_b == REG_EAX);
+    asm_x86_write_byte_2(as, OPCODE_TEST_R8_WITH_RM8, MODRM_R32(src_r32_a) | MODRM_RM_REG | MODRM_RM_R32(src_r32_b));
+}
+
+void asm_x86_setcc_r8(asm_x86_t *as, mp_uint_t jcc_type, int dest_r8) {
+    asm_x86_write_byte_3(as, OPCODE_SETCC_RM8_A, OPCODE_SETCC_RM8_B | jcc_type, MODRM_R32(0) | MODRM_RM_REG | MODRM_RM_R32(dest_r8));
+}
+
+void asm_x86_label_assign(asm_x86_t *as, mp_uint_t label) {
+    assert(label < as->max_num_labels);
+    if (as->pass < ASM_X86_PASS_EMIT) {
+        // assign label offset
+        assert(as->label_offsets[label] == -1);
+        as->label_offsets[label] = as->code_offset;
+    } else {
+        // ensure label offset has not changed from PASS_COMPUTE to PASS_EMIT
+        //printf("l%d: (at %d=%ld)\n", label, as->label_offsets[label], as->code_offset);
+        assert(as->label_offsets[label] == as->code_offset);
+    }
+}
+
+STATIC int get_label_dest(asm_x86_t *as, int label) {
+    assert(label < as->max_num_labels);
+    return as->label_offsets[label];
+}
+
+void asm_x86_jmp_label(asm_x86_t *as, mp_uint_t label) {
+    int dest = get_label_dest(as, label);
+    int rel = dest - as->code_offset;
+    if (dest >= 0 && rel < 0) {
+        // is a backwards jump, so we know the size of the jump on the first pass
+        // calculate rel assuming 8 bit relative jump
+        rel -= 2;
+        if (SIGNED_FIT8(rel)) {
+            asm_x86_write_byte_2(as, OPCODE_JMP_REL8, rel & 0xff);
+        } else {
+            rel += 2;
+            goto large_jump;
+        }
+    } else {
+        // is a forwards jump, so need to assume it's large
+        large_jump:
+        rel -= 5;
+        asm_x86_write_byte_1(as, OPCODE_JMP_REL32);
+        asm_x86_write_word32(as, rel);
+    }
+}
+
+void asm_x86_jcc_label(asm_x86_t *as, mp_uint_t jcc_type, mp_uint_t label) {
+    int dest = get_label_dest(as, label);
+    int rel = dest - as->code_offset;
+    if (dest >= 0 && rel < 0) {
+        // is a backwards jump, so we know the size of the jump on the first pass
+        // calculate rel assuming 8 bit relative jump
+        rel -= 2;
+        if (SIGNED_FIT8(rel)) {
+            asm_x86_write_byte_2(as, OPCODE_JCC_REL8 | jcc_type, rel & 0xff);
+        } else {
+            rel += 2;
+            goto large_jump;
+        }
+    } else {
+        // is a forwards jump, so need to assume it's large
+        large_jump:
+        rel -= 6;
+        asm_x86_write_byte_2(as, OPCODE_JCC_REL32_A, OPCODE_JCC_REL32_B | jcc_type);
+        asm_x86_write_word32(as, rel);
+    }
+}
+
+void asm_x86_entry(asm_x86_t *as, mp_uint_t num_locals) {
+    asm_x86_push_r32(as, REG_EBP);
+    asm_x86_mov_r32_to_r32(as, REG_ESP, REG_EBP);
+    asm_x86_sub_i32_from_r32(as, num_locals * WORD_SIZE, REG_ESP);
+    asm_x86_push_r32(as, REG_EBX);
+    as->num_locals = num_locals;
+}
+
+void asm_x86_exit(asm_x86_t *as) {
+    asm_x86_pop_r32(as, REG_EBX);
+    asm_x86_write_byte_1(as, OPCODE_LEAVE);
+    asm_x86_ret(as);
+}
+
+#if 0
+void asm_x86_push_arg(asm_x86_t *as, int src_arg_num) {
+    assert(0);
+    asm_x86_push_disp(as, REG_EBP, 8 + src_arg_num * WORD_SIZE);
+}
+
+void asm_x86_mov_arg_to_r32(asm_x86_t *as, int src_arg_num, int dest_r32) {
+    assert(0);
+    //asm_x86_mov_disp_to_r32(as, REG_EBP, 8 + src_arg_num * WORD_SIZE, dest_r32);
+}
+
+void asm_x86_mov_r32_to_arg(asm_x86_t *as, int src_r32, int dest_arg_num) {
+    assert(0);
+    //asm_x86_mov_r32_to_disp(as, src_r32, REG_EBP, 8 + dest_arg_num * WORD_SIZE);
+}
+#endif
+
+// locals:
+//  - stored on the stack in ascending order
+//  - numbered 0 through as->num_locals-1
+//  - EBP points above the last local
+//
+//                          | EPB
+//                          v
+//  l0  l1  l2  ...  l(n-1)
+//  ^                ^
+//  | low address    | high address in RAM
+//
+STATIC int asm_x86_local_offset_from_ebp(asm_x86_t *as, int local_num) {
+    return (-as->num_locals + local_num) * WORD_SIZE;
+}
+
+void asm_x86_mov_local_to_r32(asm_x86_t *as, int src_local_num, int dest_r32) {
+    asm_x86_mov_disp_to_r32(as, REG_EBP, asm_x86_local_offset_from_ebp(as, src_local_num), dest_r32);
+}
+
+void asm_x86_mov_r32_to_local(asm_x86_t *as, int src_r32, int dest_local_num) {
+    asm_x86_mov_r32_to_disp(as, src_r32, REG_EBP, asm_x86_local_offset_from_ebp(as, dest_local_num));
+}
+
+void asm_x86_mov_local_addr_to_r32(asm_x86_t *as, int local_num, int dest_r32) {
+    int offset = asm_x86_local_offset_from_ebp(as, local_num);
+    if (offset == 0) {
+        asm_x86_mov_r32_to_r32(as, REG_EBP, dest_r32);
+    } else {
+        asm_x86_lea_disp_to_r32(as, REG_EBP, offset, dest_r32);
+    }
+}
+
+#if 0
+void asm_x86_push_local(asm_x86_t *as, int local_num) {
+    asm_x86_push_disp(as, REG_EBP, asm_x86_local_offset_from_ebp(as, local_num));
+}
+
+void asm_x86_push_local_addr(asm_x86_t *as, int local_num, int temp_r32)
+{
+    asm_x86_mov_r32_to_r32(as, REG_EBP, temp_r32);
+    asm_x86_add_i32_to_r32(as, asm_x86_local_offset_from_ebp(as, local_num), temp_r32);
+    asm_x86_push_r32(as, temp_r32);
+}
+#endif
+
+void asm_x86_call_ind(asm_x86_t *as, void *ptr, mp_uint_t n_args, int temp_r32) {
+    assert(n_args <= 3);
+    if (n_args > 2) {
+        asm_x86_push_r32(as, REG_ARG_3);
+    }
+    if (n_args > 1) {
+        asm_x86_push_r32(as, REG_ARG_2);
+    }
+    if (n_args > 0) {
+        asm_x86_push_r32(as, REG_ARG_1);
+    }
+#ifdef __LP64__
+    // We wouldn't run x86 code on an x64 machine.  This is here to enable
+    // testing of the x86 emitter only.
+    asm_x86_mov_i32_to_r32(as, (int32_t)(int64_t)ptr, temp_r32);
+#else
+    // If we get here, sizeof(int) == sizeof(void*).
+    asm_x86_mov_i32_to_r32(as, (int32_t)ptr, temp_r32);
+#endif
+    asm_x86_write_byte_2(as, OPCODE_CALL_RM32, MODRM_R32(2) | MODRM_RM_REG | MODRM_RM_R32(temp_r32));
+    // this reduces code size by 2 bytes per call, but doesn't seem to speed it up at all
+    /*
+    asm_x86_write_byte_1(as, OPCODE_CALL_REL32);
+    asm_x86_write_word32(as, ptr - (void*)(as->code_base + as->code_offset + 4));
+    */
+}
+
+#endif // MICROPY_EMIT_X86