ref: ac7fed3ddfa3caf2e2c97f221e023b75ec9693ac
dir: /libstd/util+posixy-x64.s/
/* * Allocates a C string on the stack, for * use within system calls, which is the only * place the Myrddin stack should need nul-terminated * strings. * * This is in assembly, because for efficiency we * allocate the C strings on the stack, and don't adjust * %rsp when returning. */ .globl sys$cstring .globl _sys$cstring _sys$cstring: sys$cstring: /* save registers */ pushq %rbp movq %rsp,%rbp pushq %r15 pushq %rsi pushq %rdi pushq %rcx movq 8(%rbp),%r15 /* ret addr */ movq 16(%rbp),%rsi /* src */ movq 24(%rbp),%rcx /* len */ subq %rcx,%rsp /* get stack */ subq $1,%rsp /* +1 for nul */ movq %rsp,%rdi /* dest */ movq %rsp,%rax /* ret val */ subq $31,%rsp /* "unpop" the args */ andq $(~15),%rsp /* align */ cld rep movsb movb $0,(%rdi) /* terminate */ pushq %r15 /* ret addr */ /* restore registers */ movq -32(%rbp),%rcx movq -24(%rbp),%rdi movq -16(%rbp),%rsi movq -8(%rbp),%r15 movq (%rbp),%rbp ret .globl sys$alloca .globl _sys$alloca _sys$alloca: sys$alloca: /* save registers */ pushq %rbp movq %rsp,%rbp pushq %r15 pushq %rbx movq 8(%rbp),%r15 /* ret addr */ movq 16(%rbp),%rbx /* len */ /* get stack space */ subq %rbx,%rsp /* get stack space */ movq %rsp,%rax /* top of stack (return value) */ subq $31,%rsp /* "unpop" the args for return */ andq $(~15),%rsp /* align */ pushq %r15 /* ret addr */ /* restore registers */ movq -16(%rbp),%rbx movq -8(%rbp),%r15 movq (%rbp),%rbp ret