From b7c6f859d06a3a4270f98561827ba5ae360fee74 Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
Date: Sat, 13 Oct 2018 13:40:09 +1100
Subject: [PATCH] py/asmx86: Change stack management to reference locals by esp
not ebp.
The esp register is always a fixed distance below ebp, and using esp to
reference locals on the stack frees up the ebp register for general purpose
use (which is important for an architecture with only 8 user registers).
---
py/asmx86.c | 67 ++++++++++++++++++++++++++++++++---------------------
1 file changed, 40 insertions(+), 27 deletions(-)
diff --git a/py/asmx86.c b/py/asmx86.c
index 942b83fb1..81ff1d00d 100644
--- a/py/asmx86.c
+++ b/py/asmx86.c
@@ -137,14 +137,22 @@ STATIC void asm_x86_write_word32(asm_x86_t *as, int w32) {
}
STATIC void asm_x86_write_r32_disp(asm_x86_t *as, int r32, int disp_r32, int disp_offset) {
- assert(disp_r32 != ASM_X86_REG_ESP);
-
+ uint8_t rm_disp;
if (disp_offset == 0 && disp_r32 != ASM_X86_REG_EBP) {
- asm_x86_write_byte_1(as, MODRM_R32(r32) | MODRM_RM_DISP0 | MODRM_RM_R32(disp_r32));
+ rm_disp = MODRM_RM_DISP0;
} 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));
+ rm_disp = MODRM_RM_DISP8;
} else {
- asm_x86_write_byte_1(as, MODRM_R32(r32) | MODRM_RM_DISP32 | MODRM_RM_R32(disp_r32));
+ rm_disp = MODRM_RM_DISP32;
+ }
+ asm_x86_write_byte_1(as, MODRM_R32(r32) | rm_disp | MODRM_RM_R32(disp_r32));
+ if (disp_r32 == ASM_X86_REG_ESP) {
+ // Special case for esp, it needs a SIB byte
+ asm_x86_write_byte_1(as, 0x24);
+ }
+ if (rm_disp == MODRM_RM_DISP8) {
+ asm_x86_write_byte_1(as, IMM32_L0(disp_offset));
+ } else if (rm_disp == MODRM_RM_DISP32) {
asm_x86_write_word32(as, disp_offset);
}
}
@@ -390,70 +398,75 @@ void asm_x86_jcc_label(asm_x86_t *as, mp_uint_t jcc_type, mp_uint_t label) {
void asm_x86_entry(asm_x86_t *as, int num_locals) {
assert(num_locals >= 0);
asm_x86_push_r32(as, ASM_X86_REG_EBP);
- asm_x86_mov_r32_r32(as, ASM_X86_REG_EBP, ASM_X86_REG_ESP);
- if (num_locals > 0) {
- asm_x86_sub_r32_i32(as, ASM_X86_REG_ESP, num_locals * WORD_SIZE);
- }
asm_x86_push_r32(as, ASM_X86_REG_EBX);
asm_x86_push_r32(as, ASM_X86_REG_ESI);
asm_x86_push_r32(as, ASM_X86_REG_EDI);
- // TODO align stack on 16-byte boundary
+ num_locals |= 1; // make it odd so stack is aligned on 16 byte boundary
+ asm_x86_sub_r32_i32(as, ASM_X86_REG_ESP, num_locals * WORD_SIZE);
as->num_locals = num_locals;
}
void asm_x86_exit(asm_x86_t *as) {
+ asm_x86_sub_r32_i32(as, ASM_X86_REG_ESP, -as->num_locals * WORD_SIZE);
asm_x86_pop_r32(as, ASM_X86_REG_EDI);
asm_x86_pop_r32(as, ASM_X86_REG_ESI);
asm_x86_pop_r32(as, ASM_X86_REG_EBX);
- asm_x86_write_byte_1(as, OPCODE_LEAVE);
+ asm_x86_pop_r32(as, ASM_X86_REG_EBP);
asm_x86_ret(as);
}
+STATIC int asm_x86_arg_offset_from_esp(asm_x86_t *as, size_t arg_num) {
+ // Above esp are: locals, 4 saved registers, return eip, arguments
+ return (as->num_locals + 4 + 1 + arg_num) * WORD_SIZE;
+}
+
#if 0
void asm_x86_push_arg(asm_x86_t *as, int src_arg_num) {
- asm_x86_push_disp(as, ASM_X86_REG_EBP, 2 * WORD_SIZE + src_arg_num * WORD_SIZE);
+ asm_x86_push_disp(as, ASM_X86_REG_ESP, asm_x86_arg_offset_from_esp(as, src_arg_num));
}
#endif
void asm_x86_mov_arg_to_r32(asm_x86_t *as, int src_arg_num, int dest_r32) {
- asm_x86_mov_mem32_to_r32(as, ASM_X86_REG_EBP, 2 * WORD_SIZE + src_arg_num * WORD_SIZE, dest_r32);
+ asm_x86_mov_mem32_to_r32(as, ASM_X86_REG_ESP, asm_x86_arg_offset_from_esp(as, src_arg_num), dest_r32);
}
#if 0
void asm_x86_mov_r32_to_arg(asm_x86_t *as, int src_r32, int dest_arg_num) {
- asm_x86_mov_r32_to_mem32(as, src_r32, ASM_X86_REG_EBP, 2 * WORD_SIZE + dest_arg_num * WORD_SIZE);
+ asm_x86_mov_r32_to_mem32(as, src_r32, ASM_X86_REG_ESP, asm_x86_arg_offset_from_esp(as, dest_arg_num));
}
#endif
// locals:
// - stored on the stack in ascending order
// - numbered 0 through as->num_locals-1
-// - EBP points above the last local
+// - ESP points to the first local
//
-// | EBP
-// v
+// | ESP
+// 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;
+STATIC int asm_x86_local_offset_from_esp(asm_x86_t *as, int local_num) {
+ (void)as;
+ // Stack is full descending, ESP points to local0
+ return 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_mem32_to_r32(as, ASM_X86_REG_EBP, asm_x86_local_offset_from_ebp(as, src_local_num), dest_r32);
+ asm_x86_mov_mem32_to_r32(as, ASM_X86_REG_ESP, asm_x86_local_offset_from_esp(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_mem32(as, src_r32, ASM_X86_REG_EBP, asm_x86_local_offset_from_ebp(as, dest_local_num));
+ asm_x86_mov_r32_to_mem32(as, src_r32, ASM_X86_REG_ESP, asm_x86_local_offset_from_esp(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);
+ int offset = asm_x86_local_offset_from_esp(as, local_num);
if (offset == 0) {
- asm_x86_mov_r32_r32(as, dest_r32, ASM_X86_REG_EBP);
+ asm_x86_mov_r32_r32(as, dest_r32, ASM_X86_REG_ESP);
} else {
- asm_x86_lea_disp_to_r32(as, ASM_X86_REG_EBP, offset, dest_r32);
+ asm_x86_lea_disp_to_r32(as, ASM_X86_REG_ESP, offset, dest_r32);
}
}
@@ -470,13 +483,13 @@ void asm_x86_mov_reg_pcrel(asm_x86_t *as, int dest_r32, mp_uint_t label) {
#if 0
void asm_x86_push_local(asm_x86_t *as, int local_num) {
- asm_x86_push_disp(as, ASM_X86_REG_EBP, asm_x86_local_offset_from_ebp(as, local_num));
+ asm_x86_push_disp(as, ASM_X86_REG_ESP, asm_x86_local_offset_from_esp(as, local_num));
}
void asm_x86_push_local_addr(asm_x86_t *as, int local_num, int temp_r32)
{
- asm_x86_mov_r32_r32(as, temp_r32, ASM_X86_REG_EBP);
- asm_x86_add_i32_to_r32(as, asm_x86_local_offset_from_ebp(as, local_num), temp_r32);
+ asm_x86_mov_r32_r32(as, temp_r32, ASM_X86_REG_ESP);
+ asm_x86_add_i32_to_r32(as, asm_x86_local_offset_from_esp(as, local_num), temp_r32);
asm_x86_push_r32(as, temp_r32);
}
#endif
--
GitLab