1*a03411e8SWarner Losh /* 2*a03411e8SWarner Losh * Copyright (c) 2022, Netflix, Inc. 3*a03411e8SWarner Losh * 4*a03411e8SWarner Losh * SPDX-License-Identifier: BSD-2-Clause 5*a03411e8SWarner Losh */ 6*a03411e8SWarner Losh 7*a03411e8SWarner Losh /* 8*a03411e8SWarner Losh * Provides a _start routine that calls a _start_c routine that takes a pointer 9*a03411e8SWarner Losh * to the stack as documented in crt1.c. We skip the pointer to _DYNAMIC since 10*a03411e8SWarner Losh * we don't support dynamic libraries, at all. And while _start_c is our own 11*a03411e8SWarner Losh * thing, we comport to the calling conventions that glibc and musl have and 12*a03411e8SWarner Losh * make sure the second argument (%esi) is 0 for _DYNAMIC placeholder. We 13*a03411e8SWarner Losh * likely could call main directly with only a few more lines of code, but this 14*a03411e8SWarner Losh * is simple enough and concentrates all the expressable in C stuff there. We 15*a03411e8SWarner Losh * also generate eh_frames should we need to debug things (it doesn't change the 16*a03411e8SWarner Losh * genreated code, but leaves enough breadcrumbs to keep gdb happy). 17*a03411e8SWarner Losh */ 18*a03411e8SWarner Losh 19*a03411e8SWarner Losh __asm__( 20*a03411e8SWarner Losh ".text\n" /* ENTRY(_start) */ 21*a03411e8SWarner Losh ".p2align 4,0x90\n" 22*a03411e8SWarner Losh ".global _start\n" 23*a03411e8SWarner Losh ".type _start, @function\n" 24*a03411e8SWarner Losh "_start:\n" 25*a03411e8SWarner Losh ".cfi_startproc\n" 26*a03411e8SWarner Losh " xor %rbp, %rbp\n" /* Clear out the stack frame pointer */ 27*a03411e8SWarner Losh " mov %rsp, %rdi\n" /* Pass pointer to current stack with argc, argv and envp on it */ 28*a03411e8SWarner Losh " xor %rsi, %rsi\n" /* No dynamic pointer for us, to keep it simple */ 29*a03411e8SWarner Losh " andq $-16, %rsp\n" /* Align stack to 16-byte boundary */ 30*a03411e8SWarner Losh " call _start_c\n" /* Our MI code takes it from here and won't return */ 31*a03411e8SWarner Losh /* NORETURN */ 32*a03411e8SWarner Losh ".size _start, . - _start\n" /* END(_start) */ 33*a03411e8SWarner Losh ".cfi_endproc" 34*a03411e8SWarner Losh ); 35