1 /* 2 * Copyright (c) 2022, Netflix, Inc. 3 * 4 * SPDX-License-Identifier: BSD-2-Clause 5 */ 6 7 /* 8 * Provides a _start routine that calls a _start_c routine that takes a pointer 9 * to the stack as documented in crt1.c. We skip the pointer to _DYNAMIC since 10 * we don't support dynamic libraries, at all. And while _start_c is our own 11 * thing and doesn't have a second arg, we comport to the calling conventions 12 * that glibc and musl have by passing x1 as 0 for the dynamic pointer. We 13 * likely could call main directly with only a few more lines of code, but this 14 * is simple enough and concentrates all the expressable in C stuff there. We 15 * also generate eh_frames should we need to debug things (it doesn't change the 16 * genreated code, but leaves enough breadcrumbs to keep gdb happy) 17 */ 18 19 __asm__( 20 ".text\n" /* ENTRY(_start) -- can't expand and stringify, so by hand */ 21 ".align 2\n" 22 ".global _start\n" 23 ".type _start, #function\n" 24 "_start:\n" 25 ".cfi_startproc\n" 26 /* 27 * Linux zeros all registers so x29 (frame pointer) and x30 (link register) are 0. 28 */ 29 " mov x0, sp\n" /* Pointer to argc, etc kernel left on the stack */ 30 " and sp, x0, #-16\n" /* Align stack to 16-byte boundary */ 31 " b _start_c\n" /* Our MI code takes it from here */ 32 /* NORETURN */ 33 ".ltorg\n" /* END(_start) */ 34 ".cfi_endproc\n" 35 ".size _start, .-_start\n" 36 ); 37