This is the hw03 sample. Please follow the steps below.
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Fork this repo to your own github account.
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Clone the repo that you just forked.
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Under the hw03 dir, use:
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maketo build. -
make cleanto clean the ouput files.
-
-
Extract
gnu-mcu-eclipse-qemu.zipinto hw03 dir. Under the path of hw03, start emulation withmake qemu.See Lecture 02 ─ Emulation with QEMU for more details.
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The sample is a minimal program for ARM Cortex-M4 devices, which enters
while(1);after reset. Use gdb to get more details.See ESEmbedded_HW02_Example for knowing how to do the observation and how to use markdown for taking notes.
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Edit main.c.
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Make and run like the steps above.
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Please avoid using hardware dependent C Standard library functions like
printf,malloc, etc.
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How do C functions pass and return parameters? Please describe the related standard used by the Application Binary Interface (ABI) for the ARM architecture.
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Modify main.c to observe what you found.
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You have to state how you designed the observation (code), and how you performed it.
Just like how you did in HW02.
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If there are any official data that define the rules, you can also use them as references.
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Push your repo to your github. (Use .gitignore to exclude the output files like object files or executable files and the qemu bin folder)
- If you volunteer to give the presentation next week, check this.
當主程式呼叫子方程式時會牽扯到參數的傳遞，然而並不只是跳到子方程式地址然後再跳回來這麼簡單，主程式必須知道把參數放在哪個暫存器，子程式才能知道要去哪裡撈資料進行計算，計算完再將結果傳給主程式。 所以規定參數傳遞方式的協定，稱為Calling Convention。 而因為語言以及平台的不同，所以有很多種協定的方式，而我們使用的是STM32F7是ARM架構，而ARM架構下的Calling Convention協定又稱為AAPCS(ARM Architecture Procedure Call Standard)。
The standard 32-bit ARM calling convention allocates the 15 general-purpose registers as:
- r14 is the link register. (The BL instruction, used in a subroutine call, stores the return address in this register).
- r13 is the stack pointer. (The Push/Pop instructions in "Thumb" operating mode use this register only).
- r12 is the Intra-Procedure-call scratch register.
- r4 to r11: used to hold local variables.
- r0 to r3: used to hold argument values passed to a subroutine, and also hold results returned from a subroutine.
- The 16th register, r15, is the program counter.
If the type of value returned is too large to fit in r0 to r3, or whose size cannot be determined statically at compile time, then the caller must allocate space for that value at run time, and pass a pointer to that space in r0.
Subroutines must preserve the contents of r4 to r11 and the stack pointer. (Perhaps by saving them to the stack in the function prologue, then using them as scratch space, then restoring them from the stack in the function epilogue). In particular, subroutines that call other subroutines must save the return address in the link register r14 to the stack before calling those other subroutines. However, such subroutines do not need to return that value to r14—they merely need to load that value into r15, the program counter, to return.
The ARM calling convention mandates using a full-descending stack. This calling convention causes a "typical" ARM subroutine to
- In the prologue, push r4 to r11 to the stack, and push the return address in r14, to the stack. (This can be done with a single STM instruction).
- copy any passed arguments (in r0 to r3) to the local scratch registers (r4 to r11).
- allocate other local variables to the remaining local scratch registers (r4 to r11).
- do calculations and call other subroutines as necessary using BL, assuming r0 to r3, r12 and r14 will not be preserved.
- put the result in r0
- In the epilogue, pull r4 to r11 from the stack, and pull the return address to the program counter r15. (This can be done with a single LDM instruction).
修改main.c，增加三個方程式，單一引數跟多重引數以及回傳多值，透過objdump來驗證。
int oneint(int a)
{
return a+a;
}
int manyint(int a, int b, int c, int d, int e, int f)
{
return a+b+c+d+e+f;
}
void manyreturn(int a, int b, int *add, int *sub, int *mul, int *divi, int *square)
{
*add = a+b ;
*sub = a-b ;
*mul = a*b ;
*divi = a/b ;
*square =a^b;
}
void reset_handler(void)
{
int add, sub, mul, divi, square ;
oneint(1);
manyint(1, 2, 3, 4, 5, 6);
manyreturn(1, 2, &add, &sub, &mul, &divi, &square);
while (1)
;
}we get following:
Disassembly of section .mytext:
00000000 <oneint-0x8>:
0: 20000100 andcs r0, r0, r0, lsl #2
4: 000000a1 andeq r0, r0, r1, lsr #1
00000008 <oneint>:
8: b480 push {r7}
a: b083 sub sp, #12
c: af00 add r7, sp, #0
e: 6078 str r0, [r7, #4]
10: 687a ldr r2, [r7, #4]
12: 687b ldr r3, [r7, #4]
14: 4413 add r3, r2
16: 4618 mov r0, r3
18: 370c adds r7, #12
1a: 46bd mov sp, r7
1c: f85d 7b04 ldr.w r7, [sp], #4
20: 4770 bx lr
22: bf00 nop
00000024 <manyint>:
24: b480 push {r7}
26: b085 sub sp, #20
28: af00 add r7, sp, #0
2a: 60f8 str r0, [r7, #12]
2c: 60b9 str r1, [r7, #8]
2e: 607a str r2, [r7, #4]
30: 603b str r3, [r7, #0]
32: 68fa ldr r2, [r7, #12]
34: 68bb ldr r3, [r7, #8]
36: 441a add r2, r3
38: 687b ldr r3, [r7, #4]
3a: 441a add r2, r3
3c: 683b ldr r3, [r7, #0]
3e: 441a add r2, r3
40: 69bb ldr r3, [r7, #24]
42: 4413 add r3, r2
44: 4618 mov r0, r3
46: 3714 adds r7, #20
48: 46bd mov sp, r7
4a: f85d 7b04 ldr.w r7, [sp], #4
4e: 4770 bx lr
00000050 <manyreturn>:
50: b480 push {r7}
52: b085 sub sp, #20
54: af00 add r7, sp, #0
56: 60f8 str r0, [r7, #12]
58: 60b9 str r1, [r7, #8]
5a: 607a str r2, [r7, #4]
5c: 603b str r3, [r7, #0]
5e: 68fa ldr r2, [r7, #12]
60: 68bb ldr r3, [r7, #8]
62: 441a add r2, r3
64: 687b ldr r3, [r7, #4]
66: 601a str r2, [r3, #0]
68: 68fa ldr r2, [r7, #12]
6a: 68bb ldr r3, [r7, #8]
6c: 1ad2 subs r2, r2, r3
6e: 683b ldr r3, [r7, #0]
70: 601a str r2, [r3, #0]
72: 68fb ldr r3, [r7, #12]
74: 68ba ldr r2, [r7, #8]
76: fb02 f203 mul.w r2, r2, r3
7a: 69bb ldr r3, [r7, #24]
7c: 601a str r2, [r3, #0]
7e: 68fa ldr r2, [r7, #12]
80: 68bb ldr r3, [r7, #8]
82: fb92 f2f3 sdiv r2, r2, r3
86: 69fb ldr r3, [r7, #28]
88: 601a str r2, [r3, #0]
8a: 68fa ldr r2, [r7, #12]
8c: 68bb ldr r3, [r7, #8]
8e: 405a eors r2, r3
90: 6a3b ldr r3, [r7, #32]
92: 601a str r2, [r3, #0]
94: 3714 adds r7, #20
96: 46bd mov sp, r7
98: f85d 7b04 ldr.w r7, [sp], #4
9c: 4770 bx lr
9e: bf00 nop
000000a0 <reset_handler>:
a0: b590 push {r4, r7, lr}
a2: b08b sub sp, #44 ; 0x2c
a4: af04 add r7, sp, #16
a6: 2001 movs r0, #1
a8: f7ff ffae bl 8 <oneint>
ac: 2305 movs r3, #5
ae: 9300 str r3, [sp, #0]
b0: 2306 movs r3, #6
b2: 9301 str r3, [sp, #4]
b4: 2001 movs r0, #1
b6: 2102 movs r1, #2
b8: 2203 movs r2, #3
ba: 2304 movs r3, #4
bc: f7ff ffb2 bl 24 <manyint>
c0: f107 0214 add.w r2, r7, #20
c4: f107 0410 add.w r4, r7, #16
c8: f107 030c add.w r3, r7, #12
cc: 9300 str r3, [sp, #0]
ce: f107 0308 add.w r3, r7, #8
d2: 9301 str r3, [sp, #4]
d4: 1d3b adds r3, r7, #4
d6: 9302 str r3, [sp, #8]
d8: 2001 movs r0, #1
da: 2102 movs r1, #2
dc: 4623 mov r3, r4
de: f7ff ffb7 bl 50 <manyreturn>
e2: e7fe b.n e2 <reset_handler+0x42>
從objdump我們驗證到當引數超過4個時，多餘的參數會以sp來傳輸，以manyint這個function來觀察。
...
int manyint(int a, int b, int c, int d, int e, int f)
{
return a+b+c+d+e+f;
}
...
void reset_handler(void)
{
int add, sub, mul, divi, square ;
oneint(1);
manyint(1, 2, 3, 4, 5, 6);
manyreturn(1, 2, &add, &sub, &mul, &divi, &square);
while (1)
;
}再來觀察有關call manyint方程式的組語。
...
ac: 2305 movs r3, #5
ae: 9300 str r3, [sp, #0]
b0: 2306 movs r3, #6
b2: 9301 str r3, [sp, #4]
b4: 2001 movs r0, #1
b6: 2102 movs r1, #2
b8: 2203 movs r2, #3
ba: 2304 movs r3, #4
bc: f7ff ffb2 bl 24 <manyint>
...
可以發現，本次傳的參數有六個，會先將5跟6這兩個參數利用mov指令分別存到sp跟sp+4的位置，而剩下的1,2,3,4四個參數利用r0~r3來傳遞，接著利用bl跳到manyint方程式。