assembly

问题 I'm writing strncpy in MIPS, but I'm having trouble null-terminating the string. If i do not null-terminate it myself, the string goes on and on. I have tried sb $__ 0($0) but that does not seem to work... $a0 = pointer to destination array $a1 = source string $a2 = number of characters to copy strncpy: add $t1 $zero $zero #counter beq $a2 $0 done # if num chars to copy is 0, return. j cpyLoop cpyLoop: beq $t1 $a2 done # if counter == num to copy, end lb $t2 0($a1) # load the character beq

问题 I'm writing strncpy in MIPS, but I'm having trouble null-terminating the string. If i do not null-terminate it myself, the string goes on and on. I have tried sb $__ 0($0) but that does not seem to work... $a0 = pointer to destination array $a1 = source string $a2 = number of characters to copy strncpy: add $t1 $zero $zero #counter beq $a2 $0 done # if num chars to copy is 0, return. j cpyLoop cpyLoop: beq $t1 $a2 done # if counter == num to copy, end lb $t2 0($a1) # load the character beq

问题 In gcc inline assembly examples found on the net, I see register names being referenced sometimes with a single % and other times with two (i.e. %% ). It's not clear when to use a single % and when to use %% . e.g. please see below example. /* Do b = a */ int a=10, b; asm ("movl %1, %%eax;\n" "movl %%eax, %0;" : "=r" (b) /* output */ : "r" (a) /* input */ : "%eax" /* clobbered register */ ); This example which uses %% prefix for EAX register compiles fine on my x86 machine (Linux RedHat 5.6

问题 In gcc inline assembly examples found on the net, I see register names being referenced sometimes with a single % and other times with two (i.e. %% ). It's not clear when to use a single % and when to use %% . e.g. please see below example. /* Do b = a */ int a=10, b; asm ("movl %1, %%eax;\n" "movl %%eax, %0;" : "=r" (b) /* output */ : "r" (a) /* input */ : "%eax" /* clobbered register */ ); This example which uses %% prefix for EAX register compiles fine on my x86 machine (Linux RedHat 5.6

问题 I want to build Custom Portable executable using NASM. After getting executable using command nasm -f bin program.asm -o program.exe it crashes and gives error similar to this Below you can see the code. bits 64 %define BASE 400000h ALIGNMENT equ 512 %define SECTALIGN 8192 STD_OUTPUT_HANDLE equ -11 NULL equ 0 %define ROUND(v, a) (((v + a - 1) / a) * a) %define ALIGNED(v) (ROUND(v, ALIGNMENT)) %define RVA(obj) (obj - BASE) section header progbits start=0 vstart=BASE mz_hdr: dw "MZ" ; DOS magic

问题 I want to build Custom Portable executable using NASM. After getting executable using command nasm -f bin program.asm -o program.exe it crashes and gives error similar to this Below you can see the code. bits 64 %define BASE 400000h ALIGNMENT equ 512 %define SECTALIGN 8192 STD_OUTPUT_HANDLE equ -11 NULL equ 0 %define ROUND(v, a) (((v + a - 1) / a) * a) %define ALIGNED(v) (ROUND(v, ALIGNMENT)) %define RVA(obj) (obj - BASE) section header progbits start=0 vstart=BASE mz_hdr: dw "MZ" ; DOS magic

问题 Are there any other processor registers (e.g. flags) besides the architectural registers (eax, ebx,.) in x86 for which RAW dependencies need to be enforced by the scoreboard in pipelined processors? 回答1: Literally every register guarantees that if you write it, later instructions will read the new value. x86 is defined in terms of serial execution; pipelining and out-of-order exec need to preserve that illusion for everything , including segment registers, FP rounding modes, control and debug

问题 first, if somebody knows a function of the Standard C Library, that prints a string without looking for a binary zero, but requires the number of characters to draw, please tell me! Otherwise, I have this problem: void printStringWithLength(char *str_ptr, int n_chars){ asm("mov 4, %rax");//Function number (write) asm("mov 1, %rbx");//File descriptor (stdout) asm("mov $str_ptr, %rcx"); asm("mov $n_chars, %rdx"); asm("int 0x80"); return; } GCC tells the following error to the "int" instruction:

问题 first, if somebody knows a function of the Standard C Library, that prints a string without looking for a binary zero, but requires the number of characters to draw, please tell me! Otherwise, I have this problem: void printStringWithLength(char *str_ptr, int n_chars){ asm("mov 4, %rax");//Function number (write) asm("mov 1, %rbx");//File descriptor (stdout) asm("mov $str_ptr, %rcx"); asm("mov $n_chars, %rdx"); asm("int 0x80"); return; } GCC tells the following error to the "int" instruction:

问题 I have the inline assembly code: #define read_msr(index, buf) asm volatile ("rdmsr" : "=d"(buf[1]), "=a"(buf[0]) : "c"(index)) The code using this macro: u32 buf[2]; read_msr(0x173, buf); I found the disassembly is(using gnu toolchain): mov eax,0x173 mov ecx,eax rdmsr mov DWORD PTR [rbp-0xc],edx mov DWORD PTR [rbp-0x10],eax The question is that 0x173 is less than 0xffff, why gcc does not use "mov cx, 0x173"? Will the gcc analysis the following instruction "rdmsr"? Will the gcc always know the