ref: 4f34933ae3e4dffaefb084081e8c5330dd864b94
dir: /libstd/start-linux.s/
.data
/* std._environment : byte[:][:] */
.globl std$_environment
std$_environment:
.envbase:
.quad 0 /* env size */
.envlen:
.quad 0 /* env ptr */
.globl std$__cenvp
std$__cenvp:
.quad 0
.text
/*
* counts the length of the string pointed to
* by %r8, returning len in %r9. Does not modify
* any registers outside of %r9
*/
cstrlen:
xorq %r9,%r9
jmp .lentest
.lenloop:
incq %r9
.lentest:
cmpb $0,(%r8,%r9)
jne .lenloop
ret
/*
* Counts the size of the null terminated string vector
* pointed to by %rbx. Clobbers %r10,%r11
*/
count:
xorq %r9,%r9
movq %rbx,%r11
.countloop:
movq (%r11),%r10
testq %r10,%r10
jz .countdone
addq $1,%r9
addq $8,%r11
jmp .countloop
.countdone:
ret
/*
* iterate over the strings for argc, and put
* them into the args array.
*
* argc in %rax, argv in %rbx, dest vector in %rcx
*/
cvt:
jmp .cvttest
.cvtloop:
subq $1,%rax
movq (%rbx),%r8
call cstrlen
movq %r8, (%rcx)
movq %r9, 8(%rcx)
addq $8, %rbx
addq $16, %rcx
.cvttest:
testq %rax,%rax
jnz .cvtloop
.cvtdone:
ret
/*
* The entry point for the whole program.
* This is called by the OS. In order, it:
* - Sets up all argc entries as slices
* - Sets up all envp entries as slices
* - Converts argc/argv to a slice
* - Stashes envp in std._environment
* - Stashes a raw envp copy in __cenvp (for syscalls to use)
* - Calls main()
*/
.globl _start
_start:
/* turn args into a slice */
movq %rsp,%rbp
/* stack allocate sizeof(byte[:])*(argc + len(envp)) */
movq (%rbp),%rax
leaq 16(%rbp,%rax,8), %rbx /* argp = argv + 8*argc + 8 */
call count
addq %r9,%rax
imulq $16,%rax
subq %rax,%rsp
movq %rsp, %rdx /* saved args[:] */
/* convert envp to byte[:][:] for std._environment */
movq (%rbp),%rax
leaq 16(%rbp,%rax,8), %rbx /* envp = argv + 8*argc + 8 */
/* store envp for some syscalls to use without converting */
movq %rbx,std$__cenvp(%rip)
movq %r9,%rax
movq %rsp, %rcx
movq %r9,.envlen
movq %rdx,.envbase
call cvt
movq %rcx,%rdx
/* convert argc, argv to byte[:][:] for args. */
movq (%rbp), %rax /* argc */
leaq 8(%rbp), %rbx /* argv */
movq (%rbp), %rsi /* saved argc */
call cvt
pushq %rsi
pushq %rdx
/* enter the main program */
call main
/* exit(0) */
xorq %rdi,%rdi
movq $60,%rax
syscall