Asm

clang++ -S -O3 -march=haswell -mllvm --x86-asm-syntax=intel

Set zero flag from value

test ri ri

Parameter

The parameter will be put in stack and the first value is the count of the args and the second args is the program name.

ax accumulator register bx base register cx counter register dx data register

bp - register base pointer (start of stack) sp - register stack pointer (current location in stack, growing downwards) si - register source index (source for data copies) di - register destination index (destination for data copies)

r8 - register 8 r9 - register 9 r10 - register 10 r11 - register 11 r12 - register 12 r13 - register 13 r14 - register 14 r15 - register 15

64-bit registers using the ‘r’ prefix: rax, r15 32-bit registers using the ’e’ prefix (original registers: e_x) or ’d’ suffix (added registers: r__d): eax, r15d (double word) 16-bit eegisters using no prefix (original registers: _x) or a ‘w’ suffix (added registers: r__w): ax, r15w 8-bit registers using ‘h’ (“high byte” of 16 bits) suffix (original registers - bits 8-15: _h): ah, bh 8-bit registers using ’l’ (“low byte” of 16 bits) suffix (original registers - bits 0-7: _l) or ‘b’ suffix (added registers: r__b): al, bl, r15b

rdi - first argument rsi - second argument rdx - third argument rcx - fourth argument r8 - fifth argument r9 - sixth

system call

First six arguments are in rdi, rsi, rdx, rcx, r8d, r9d; remaining arguments are on the stack. For syscalls, the syscall number is in rax. Return value is in rax. The called routine is expected to preserve rsp,rbp, rbx, r12, r13, r14, and r15 but may trample any other registers.

EFLAGS(program status and control) register

• carry flag is set when there is a carry out Of the most-significant bit.
• overflow flag is set when there is a carry into the most significant bit.
• Parity flag least-significant byte)包含偶数个 1 位则该位置 1，否则清零
• Adjust flag 如果算术操作在结果的第 3 位发生进位或借位则将该标志置 1，否则清零。这个标志在 BCD(binary-code decimal)算术运算中被使用
• zero flag
• sign flag

看内存

内存地址格式为： 0x4bdc(%rip), 一般是全局变量，全局区（数据段） 内存地址格式为：-0x78(%rbp), 一般是局部变量，栈空间 存地址格式为：0x10(%rax), 一般是堆空间