From 00fc82f17cff9295387d516384ecdc443acb1b22 Mon Sep 17 00:00:00 2001 From: Bradley Morgan Date: Sat, 3 Oct 2026 18:57:38 +0000 Subject: tashaboot: arm64 bringup, semihosting payload loader consoles on the pl011 the dtb points at, walks the memory node and chosen, loads an arm64 kernel Image over semihosting and jumps to it with the documented register state. string functions, printf and libfdt are vendored from lk (lk2nd) and u-boot so the libc surface is the one those projects already proved. built and booted on qemu virt, payload exits clean through semihosting. --- test/payload.S | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 test/payload.S (limited to 'test') diff --git a/test/payload.S b/test/payload.S new file mode 100644 index 0000000..d1891a2 --- /dev/null +++ b/test/payload.S @@ -0,0 +1,52 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * payload.S - tiny arm64 image for testing tashaboot. carries the real + * Image header from Documentation/arch/arm64/booting.rst, prints one + * line on the virt uart, parks. built with the same conventions the + * kernel itself uses so the header math in tashaboot is exercised for + * real, not against a fake. + * + * Copyright (C) 2026 Bradley Morgan + */ + +#include + +/* the header the bootloader validates */ +#define ARM64_IMAGE_MAGIC 0x644d5241 + +.section .text.head +.globl _start +_start: + /* code0/code1: branch over the header, like the kernel does */ + b 1f + .long 0 + + /* text_offset, 0x80000 like every kernel since forever */ + .quad 0x80000 + /* image_size, filled at build time by scripts/mkpayload.sh */ + .quad payload_end - _start + /* flags, bit 3 = anywhere in memory is fine */ + .quad (1 << 3) + .quad 0 + .quad 0 + .quad 0 + /* magic "ARM\x64" */ + .long ARM64_IMAGE_MAGIC + .long 0 +1: + /* the payload entry: x0 = dtb from the bootloader */ + ldr x1, =0x09000000 /* pl011 on qemu virt */ + adr x2, msg +2: ldrb w3, [x2], #1 + cbz w3, 3f + str w3, [x1] + b 2b +3: /* clean exit through semihosting, proof we got here */ + mov x0, #0x18 /* SYS_EXIT */ + ldr x1, =0x20026 /* ADP_Stopped_ApplicationExit */ + hlt #0xF000 + b 3b + +msg: .asciz "payload: alive, tashaboot jumped here\n" + .balign 8 +payload_end: -- cgit v1.2.3