vhaudiquet
64e19c213a
Minimal freestanding arm64 binary that depthcharge boots as a kernel: parses depthcharge's /firmware/coreboot DTB node, walks the coreboot table, finds LB_TAG_FRAMEBUFFER, and paints red/yellow/green/blue checkpoints (~2s each) into the live boot-splash framebuffer. Verified against coreboot tables header, Linux arm64 booting.rst, and depthcharge's fit.c/boot64.c. Host parser tests pass against the live /sys/firmware/fdt; full red->yellow->green->blue sequence verified end-to-end under qemu-system-aarch64; packed image verifies with the ChromeOS devkeys.
52 lines
1.6 KiB
ArmAsm
52 lines
1.6 KiB
ArmAsm
/*
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* krane-fb-stub — minimal arm64 "hello framebuffer" payload for depthcharge.
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*
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* Entry contract (Linux arm64 boot protocol, verified against
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* linux/Documentation/arch/arm64/booting.rst and depthcharge
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* src/arch/arm/boot64.c + boot64_asm.S):
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* - depthcharge copies the (uncompressed) kernel image to a random
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* 2 MiB-aligned slot in RAM, then jumps to its first byte with
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* x0 = phys addr of flattened DTB, x1..x3 = 0, MMU off.
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* - => everything must be position-independent (PC-relative only).
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*
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* 64-byte arm64 Image header (booting.rst):
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* 0x00 code0 b past header (this is where we are entered)
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* 0x04 code1 unused
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* 0x08 text_offset 0 (image sits AT the 2M-aligned base)
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* 0x10 image_size patched by build.sh to the final file size
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* 0x18 flags bit3 = "place anywhere in 48-bit range"
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* 0x20..0x37 reserved = 0
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* 0x38 magic 0x644d5241 "ARM\x64" (checked by depthcharge)
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* 0x3c res5 0
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*/
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.section .head, "ax"
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.globl _start
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_start:
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b real_start /* code0: branch to 0x40 */
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.word 0 /* code1 */
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.quad 0 /* text_offset */
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.quad 0 /* image_size — PATCHED by build.sh */
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.quad 1 /* flags: bit3 set (KASLR placement) */
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.quad 0 /* res2 */
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.quad 0 /* res3 */
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.quad 0 /* res4 */
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.word 0x644d5241 /* magic "ARM\x64" */
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.word 0 /* res5 */
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.section .text, "ax"
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real_start:
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/* depthcharge's SP is dead; use our own stack inside the image */
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adrp x4, stack_top
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add x4, x4, :lo12:stack_top
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mov sp, x4
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bl cmain
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1: b 1b /* cmain never returns; belt+braces halt */
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.section .stacksec, "aw"
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.align 4
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.globl stack_top
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stack_bottom:
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.zero 16384
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stack_top:
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