c语言汇编
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【转载】:http://blog.csdn.net/mindview/article/details/2188569
int main() ...{
short x=6;
short y=9;
short z;
z = x+y;
return 0;
}
short x=6;
short y=9;
short z;
z = x+y;
return 0;
}
.file "CSCILab03-1.cpp"
; This is the input source file. This will probably make it into the
; assembler output as some kind of debug record for later debugging.
.text
.align 2
; .text is a section command (.data and .bss are others). All program
; and constant data typically goes into .text. Global initialised data
; should be in .data, and uninitialised globals should be in .bss
.globl main
.type main, @function
; Declare a global symbol, and set it's type to be a function.
main:
; main starts here :)
leal 4(%esp), %ecx ; Save the original stack pointer
andl $-16, %esp ; -16 is 0xFFFFFFF0, which clears the bottom
; 4 bits of the stack pointer (esp). The effect
; of this is to ensure the stack remains 16-byte
; aligned for the most efficient access to any
; data type;
pushl -4(%ecx) ; push the original stack pointer
; These first 3 instructions are only something you will see in main()
; Put the same code into another function, and it will just begin with
; the saving and setting up of ebp.
pushl %ebp ; Save original base pointer (ebp)
movl %esp, %ebp ; Establish a new base pointer where the stack is now.
pushl %ecx ; Save it
subl $16, %esp ; Allocate some space for local variables.
movw $6, -10(%ebp) ; short x=6;
movw $9, -8(%ebp) ; short y=9;
movzwl -10(%ebp), %edx ; Move (short)x into edx, and clear the MSW
movzwl -8(%ebp), %eax ; Move (short)y into eax, and clear the MSW
leal (%edx,%eax), %eax ; one of many ways of performing an addition.
movw %ax, -6(%ebp) ; Move (short)ax into z
movl $0, %eax ; return 0; (well, putting 0 into the return register)
addl $16, %esp ; remove the local variables
popl %ecx ; restore a register
popl %ebp ; restore another register
leal -4(%ecx), %esp ; restore the original stack pointer
; this is another 'main only' step, see the start
ret ; Adiós amigo
.LFE2:
.size main, .-main
; Some internal symbol which indicates how many bytes the main function
; occupies.
.globl __gxx_personality_v0
; gxx_personality is something which g++ emits, for what, I don't know.
.ident "GCC: (GNU) 4.1.1 20070105 (Red Hat 4.1.1-52)"
; More identification of what generated this assembly code.
.section .note.GNU-stack,"",@progbits
; Dunno what this is for.
.file "CSCILab03-1.cpp" ; This is the input source file. This will probably make it into the ; assembler output as some kind of debug record for later debugging. .text .align 2 ; .text is a section command (.data and .bss are others). All program ; and constant data typically goes into .text. Global initialised data ; should be in .data, and uninitialised globals should be in .bss .globl main .type main, @function ; Declare a global symbol, and set it's type to be a function. main: ; main starts here :) leal 4(%esp), %ecx ; Save the original stack pointer andl $-16, %esp ; -16 is 0xFFFFFFF0, which clears the bottom ; 4 bits of the stack pointer (esp). The effect ; of this is to ensure the stack remains 16-byte ; aligned for the most efficient access to any ; data type; pushl -4(%ecx) ; push the original stack pointer ; These first 3 instructions are only something you will see in main() ; Put the same code into another function, and it will just begin with ; the saving and setting up of ebp. pushl %ebp ; Save original base pointer (ebp) movl %esp, %ebp ; Establish a new base pointer where the stack is now. pushl %ecx ; Save it subl $16, %esp ; Allocate some space for local variables. movw $6, -10(%ebp) ; short x=6; movw $9, -8(%ebp) ; short y=9; movzwl -10(%ebp), %edx ; Move (short)x into edx, and clear the MSW movzwl -8(%ebp), %eax ; Move (short)y into eax, and clear the MSW leal (%edx,%eax), %eax ; one of many ways of performing an addition. movw %ax, -6(%ebp) ; Move (short)ax into z movl $0, %eax ; return 0; (well, putting 0 into the return register) addl $16, %esp ; remove the local variables popl %ecx ; restore a register popl %ebp ; restore another register leal -4(%ecx), %esp ; restore the original stack pointer ; this is another 'main only' step, see the start ret ; Adiós amigo .LFE2: .size main, .-main ; Some internal symbol which indicates how many bytes the main function ; occupies. .globl __gxx_personality_v0 ; gxx_personality is something which g++ emits, for what, I don't know. .ident "GCC: (GNU) 4.1.1 20070105 (Red Hat 4.1.1-52)" ; More identification of what generated this assembly code. .section .note.GNU-stack,"",@progbits ; Dunno what this is for.
The %ebp is the base pointer, also known as the stack frame pointer. It is a fixed register within the scope of a single function.
All local variables (a negative offset) and parameters (a positive offset) are accessed relative to the %ebp established at the start of the function.
Since 4(%ebp) is the previous frame pointer, you can use this (as debuggers do) to walk up the stack to examine the state of any function in the current call hierarchy. The 'bt' command in GDB will use this chain for example.
; This is the input source file. This will probably make it into the
; assembler output as some kind of debug record for later debugging.
.text
.align 2
; .text is a section command (.data and .bss are others). All program
; and constant data typically goes into .text. Global initialised data
; should be in .data, and uninitialised globals should be in .bss
.globl main
.type main, @function
; Declare a global symbol, and set it's type to be a function.
main:
; main starts here :)
leal 4(%esp), %ecx ; Save the original stack pointer
andl $-16, %esp ; -16 is 0xFFFFFFF0, which clears the bottom
; 4 bits of the stack pointer (esp). The effect
; of this is to ensure the stack remains 16-byte
; aligned for the most efficient access to any
; data type;
pushl -4(%ecx) ; push the original stack pointer
; These first 3 instructions are only something you will see in main()
; Put the same code into another function, and it will just begin with
; the saving and setting up of ebp.
pushl %ebp ; Save original base pointer (ebp)
movl %esp, %ebp ; Establish a new base pointer where the stack is now.
pushl %ecx ; Save it
subl $16, %esp ; Allocate some space for local variables.
movw $6, -10(%ebp) ; short x=6;
movw $9, -8(%ebp) ; short y=9;
movzwl -10(%ebp), %edx ; Move (short)x into edx, and clear the MSW
movzwl -8(%ebp), %eax ; Move (short)y into eax, and clear the MSW
leal (%edx,%eax), %eax ; one of many ways of performing an addition.
movw %ax, -6(%ebp) ; Move (short)ax into z
movl $0, %eax ; return 0; (well, putting 0 into the return register)
addl $16, %esp ; remove the local variables
popl %ecx ; restore a register
popl %ebp ; restore another register
leal -4(%ecx), %esp ; restore the original stack pointer
; this is another 'main only' step, see the start
ret ; Adiós amigo
.LFE2:
.size main, .-main
; Some internal symbol which indicates how many bytes the main function
; occupies.
.globl __gxx_personality_v0
; gxx_personality is something which g++ emits, for what, I don't know.
.ident "GCC: (GNU) 4.1.1 20070105 (Red Hat 4.1.1-52)"
; More identification of what generated this assembly code.
.section .note.GNU-stack,"",@progbits
; Dunno what this is for.
.file "CSCILab03-1.cpp" ; This is the input source file. This will probably make it into the ; assembler output as some kind of debug record for later debugging. .text .align 2 ; .text is a section command (.data and .bss are others). All program ; and constant data typically goes into .text. Global initialised data ; should be in .data, and uninitialised globals should be in .bss .globl main .type main, @function ; Declare a global symbol, and set it's type to be a function. main: ; main starts here :) leal 4(%esp), %ecx ; Save the original stack pointer andl $-16, %esp ; -16 is 0xFFFFFFF0, which clears the bottom ; 4 bits of the stack pointer (esp). The effect ; of this is to ensure the stack remains 16-byte ; aligned for the most efficient access to any ; data type; pushl -4(%ecx) ; push the original stack pointer ; These first 3 instructions are only something you will see in main() ; Put the same code into another function, and it will just begin with ; the saving and setting up of ebp. pushl %ebp ; Save original base pointer (ebp) movl %esp, %ebp ; Establish a new base pointer where the stack is now. pushl %ecx ; Save it subl $16, %esp ; Allocate some space for local variables. movw $6, -10(%ebp) ; short x=6; movw $9, -8(%ebp) ; short y=9; movzwl -10(%ebp), %edx ; Move (short)x into edx, and clear the MSW movzwl -8(%ebp), %eax ; Move (short)y into eax, and clear the MSW leal (%edx,%eax), %eax ; one of many ways of performing an addition. movw %ax, -6(%ebp) ; Move (short)ax into z movl $0, %eax ; return 0; (well, putting 0 into the return register) addl $16, %esp ; remove the local variables popl %ecx ; restore a register popl %ebp ; restore another register leal -4(%ecx), %esp ; restore the original stack pointer ; this is another 'main only' step, see the start ret ; Adiós amigo .LFE2: .size main, .-main ; Some internal symbol which indicates how many bytes the main function ; occupies. .globl __gxx_personality_v0 ; gxx_personality is something which g++ emits, for what, I don't know. .ident "GCC: (GNU) 4.1.1 20070105 (Red Hat 4.1.1-52)" ; More identification of what generated this assembly code. .section .note.GNU-stack,"",@progbits ; Dunno what this is for.
The %ebp is the base pointer, also known as the stack frame pointer. It is a fixed register within the scope of a single function.
All local variables (a negative offset) and parameters (a positive offset) are accessed relative to the %ebp established at the start of the function.
Since 4(%ebp) is the previous frame pointer, you can use this (as debuggers do) to walk up the stack to examine the state of any function in the current call hierarchy. The 'bt' command in GDB will use this chain for example.
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