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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).
This commit is contained in:
Damien George 2018-10-13 13:40:09 +11:00
parent 8e4b4bac70
commit b7c6f859d0
1 changed files with 40 additions and 27 deletions
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67
py/asmx86.c
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@ -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