本文講解了C語言運行在MIPS體系中結構體傳參的情況
硬件平臺:Loongson 3A3000
系統:uos
在《see MIPS run》中11.2.5中描述到,會將結構體成員壓縮到各個arg寄存器中進行傳遞
“we have to pack the register with data to mimic the arrangement of data in memory.”
- C語言代碼:
構造一個函數,參數爲結構體,在main函數中調用函數,並傳入結構體
#include <stdio.h>
#include <stdint.h>
struct shape{
uint32_t a;
uint16_t b
};
void test(struct shape sp){
uint32_t c = sp.a + sp.b;
printf("%d \n", c);
}
void main()
{
struct shape sp;
sp.a = 12;
sp.b = 32;
test(sp);
}
- 彙編代碼
0000000000000b00 <test>:
b00: 67bdffc0 daddiu sp,sp,-64
b04: ffbf0038 sd ra,56(sp)
b08: ffbe0030 sd s8,48(sp)
b0c: ffbc0028 sd gp,40(sp)
b10: 03a0f025 move s8,sp
b14: 3c1c0002 lui gp,0x2
b18: 0399e02d daddu gp,gp,t9
b1c: 679c8320 daddiu gp,gp,-31968
b20: ffc40010 sd a0,16(s8)
b24: 8fc30010 lw v1,16(s8)
b28: 97c20014 lhu v0,20(s8)
b2c: 00621021 addu v0,v1,v0
0000000000000b74 <main>:
b74: 67bdffd0 daddiu sp,sp,-48
b78: ffbf0028 sd ra,40(sp)
b7c: ffbe0020 sd s8,32(sp)
b80: ffbc0018 sd gp,24(sp)
b84: 03a0f025 move s8,sp
b88: 3c1c0002 lui gp,0x2
b8c: 0399e02d daddu gp,gp,t9
b90: 679c82ac daddiu gp,gp,-32084
b94: 2402000c li v0,12 //加載立即數到V0
b98: afc20000 sw v0,0(s8) //保存到棧中
b9c: 24020020 li v0,32 //加載立即數到V0
ba0: a7c20004 sh v0,4(s8) //保存到棧中
ba4: dfc40000 ld a0,0(s8)
ba8: df828058 ld v0,-32680(gp)
bac: 0040c825 move t9,v0
bb0: 0411ffd3 bal b00 <test>
- 在ba0代碼執行完畢後棧內數據情況如下
- ba4 ld a0,0(s8); 把棧中8個字節加載到了a0寄存器,即圖中0~8中的數據,即結構體中的a、b
- b20 sd a0,16(s8); 把a0,放到棧中16offset
- b24 lw v1,16(s8); 從棧中16offset讀取前4個字節
- b28 lhu v0,20(s8);從棧中20offset讀取剩下兩個字節