x86-64

问题 [bits 32] global _start section .data str_hello db "HelloWorld", 0xa str_hello_length db $-str_hello section .text _start: mov ebx, 1 ; stdout file descriptor mov ecx, str_hello ; pointer to string of characters that will be displayed mov edx, [str_hello_length] ; count outputs Relative addressing mov eax, 4 ; sys_write int 0x80 ; linux kernel system call mov ebx, 0 ; exit status zero mov eax, 1 ; sys_exit int 0x80 ; linux kernel system call The fundamental thing here is that I need to have

问题 I'm reading a textbook which shows assembly code based on C code: C code: void echo() { char buf[8]; otherFunction(buf); } assembly code: echo: subq $24, %rsp //Allocate 24 bytes on stack, but why allocate 24 instead of 8 bytes? movq %rsp, %rdi //Compute buf as %rsp call otherFunction I don't understand why stack pointer %rsp is decremented by 24 bytes. I only assign 8 bytes' buffer as char buf[8]; , and there no callee saved registers to push on stack, shouldn't the instruction be subq $8,

问题 I'm reading a textbook which shows assembly code based on C code: C code: void echo() { char buf[8]; otherFunction(buf); } assembly code: echo: subq $24, %rsp //Allocate 24 bytes on stack, but why allocate 24 instead of 8 bytes? movq %rsp, %rdi //Compute buf as %rsp call otherFunction I don't understand why stack pointer %rsp is decremented by 24 bytes. I only assign 8 bytes' buffer as char buf[8]; , and there no callee saved registers to push on stack, shouldn't the instruction be subq $8,

问题 My question arises from a simple curiosity: Why in x64 some of the opcodes are invalid (06, 07 for example), whereas in x86 are used for fairly basic instructions (06 and 07 being push and pop)? I though that those simplest instructions would do nicely in both architectures. Why they disabled some of those simple instructions in x64? Why wouldn't they work? Why they disabled some opcodes, creating holes in opcode list, when they could instead assign them to x64 versions of instructions?

问题 During reading of an Intel manual book I came across the following: On processors that support Intel 64 architecture, the IA32_SYSENTER_ESP field and the IA32_SYSENTER_EIP field must each contain a canonical address. What is a 'canonical address'? 回答1: I suggest that you download the full software developer's manual. The documentation is available in separate volumes, but that link gives you all seven volumes in a single massive PDF, which makes it easier to search for things. The answer is

问题 During reading of an Intel manual book I came across the following: On processors that support Intel 64 architecture, the IA32_SYSENTER_ESP field and the IA32_SYSENTER_EIP field must each contain a canonical address. What is a 'canonical address'? 回答1: I suggest that you download the full software developer's manual. The documentation is available in separate volumes, but that link gives you all seven volumes in a single massive PDF, which makes it easier to search for things. The answer is

问题 I have compiled this function: void print_ints(int len, ...){ va_list args; va_start(args, len); for(int i =0; i<len ; i++) { int val = va_arg(args,int); printf("i:%i\tval:%i\n",i,val); } va_end(args); } into this assembly: print_ints: pushq %rbp # movq %rsp, %rbp #, subq $224, %rsp #, movl %edi, -212(%rbp) # len, len movq %rsi, -168(%rbp) #, movq %rdx, -160(%rbp) #, movq %rcx, -152(%rbp) #, movq %r8, -144(%rbp) #, movq %r9, -136(%rbp) #, testb %al, %al # je .L7 #, movaps %xmm0, -128(%rbp) #,

问题 I have compiled this function: void print_ints(int len, ...){ va_list args; va_start(args, len); for(int i =0; i<len ; i++) { int val = va_arg(args,int); printf("i:%i\tval:%i\n",i,val); } va_end(args); } into this assembly: print_ints: pushq %rbp # movq %rsp, %rbp #, subq $224, %rsp #, movl %edi, -212(%rbp) # len, len movq %rsi, -168(%rbp) #, movq %rdx, -160(%rbp) #, movq %rcx, -152(%rbp) #, movq %r8, -144(%rbp) #, movq %r9, -136(%rbp) #, testb %al, %al # je .L7 #, movaps %xmm0, -128(%rbp) #,

问题 Having this in gas: .text .globl main main: xor %eax, %eax lea str(%rip), %rdi call printf call exit str: .byte 0x7F, "ELF", 1,1,1,0 I thought the .byte directive could be concatenate as in nasm db 0x7F, "ELF", 1, 1, 1, 0 ; e_ident source : http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html 回答1: In GAS syntax, "ELF" is a symbol reference to the symbol name ELF , not a multi-char string. In the context of .byte directive, it's only looking for a number, not a possible string. And

问题 Having this in gas: .text .globl main main: xor %eax, %eax lea str(%rip), %rdi call printf call exit str: .byte 0x7F, "ELF", 1,1,1,0 I thought the .byte directive could be concatenate as in nasm db 0x7F, "ELF", 1, 1, 1, 0 ; e_ident source : http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html 回答1: In GAS syntax, "ELF" is a symbol reference to the symbol name ELF , not a multi-char string. In the context of .byte directive, it's only looking for a number, not a possible string. And