boot2

Playing with the boostrap
git clone https://git.ryansepassi.com/git/boot2.git
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boot6-gen-runscm.sh (4433B)

      1 #!/bin/sh
      2 ## boot6-gen-runscm.sh — emit run.scm driving tcc3 to build seed-kernel.
      3 ##
      4 ## tcc3 -c each translation unit (kernel.S, kernel.c, mem.c) → .o, then
      5 ## tcc3 links + emits a flat arm64 boot Image directly (no `ld -T
      6 ## kernel.lds`, no objcopy).  The link line is three tcc flags:
      7 ##
      8 ##   -nostdlib -static          freestanding link, no startfiles
      9 ##   -Wl,-Ttext=0x40080000      base address (arm64 RAM_BASE +
     10 ##                              text_offset; QEMU's `-kernel` loads
     11 ##                              us here)
     12 ##   -Wl,--oformat=binary       flat-bytes output (objcopy -O binary
     13 ##                              equivalent).  Required because QEMU's
     14 ##                              `-kernel <ELF>` path doesn't run the
     15 ##                              arm64 boot wrapper that puts DTB in
     16 ##                              x0 — only the flat-Image path does.
     17 ##                              Detection is by `ARM\x64` magic at
     18 ##                              file offset 0x38, which is in
     19 ##                              kernel.S's Image header at the top of
     20 ##                              `.text`.
     21 ##
     22 ## Everything else the kernel needs from the linker is supplied by
     23 ## conventions tcc3 already honors:
     24 ##
     25 ##   _start         hard-coded entry symbol; kernel.S's arm64 Image
     26 ##                  header is named `_start` (not `_head`) so this works
     27 ##                  out of the box.
     28 ##   __bss_start    auto-defined at the start of merged .bss via the
     29 ##                  `bss-start-symbol` simple-patch.
     30 ##   _end           auto-defined by stock tcc at the end of merged .bss
     31 ##                  (tcc_add_linker_symbols).  kernel.S uses it to
     32 ##                  bracket the bss-zero loop and to compute the
     33 ##                  Image-header `image_size` field; kernel.c uses it
     34 ##                  to place the kernel heap above the loaded image.
     35 ##
     36 ## Usage: bootprep/boot6-gen-runscm.sh <arch>
     37 ##   Writes build/<arch>/src/run/boot6.scm.
     38 
     39 set -eu
     40 [ "$#" -eq 1 ] || { echo "usage: $0 <arch>" >&2; exit 2; }
     41 ARCH=$1
     42 OUT=build/$ARCH/src/run/boot6.scm
     43 mkdir -p "$(dirname "$OUT")"
     44 
     45 # Per-arch link parameters.  aarch64 alone needs --oformat=binary because
     46 # QEMU's `-kernel <ELF>` path skips the arm64 boot wrapper that puts DTB
     47 # in x0 — only the flat-Image path honors it (detected via the `ARM\x64`
     48 # magic at file offset 0x38 in kernel.S's Image header).  amd64/riscv64
     49 # stay as ELF: QEMU's `-kernel` path on those arches consumes ELF
     50 # directly (PVH note for amd64, OpenSBI for riscv64).
     51 case "$ARCH" in
     52     aarch64) TTEXT=0x40080000; OUT_FILE=Image;      LINK_OFORMAT='"-Wl,--oformat=binary"' ;;
     53     amd64)   TTEXT=0x40000000; OUT_FILE=kernel.elf; LINK_OFORMAT= ;;
     54     riscv64) TTEXT=0x80200000; OUT_FILE=kernel.elf; LINK_OFORMAT= ;;
     55     *) echo "boot6-gen: unsupported arch '$ARCH'" >&2; exit 2 ;;
     56 esac
     57 
     58 # Kernel CFLAGS — freestanding, static, no host startfiles. We omit gcc's
     59 # -mgeneral-regs-only (no tcc equivalent); kernel.S enables CPACR_EL1.FPEN
     60 # in stext before the first `bl kmain`, so tcc's SIMD callee-saves in
     61 # function prologues don't trap.
     62 KCFLAGS='"-nostdlib" "-ffreestanding" "-static"'
     63 
     64 cat > "$OUT" <<EOF
     65 ;; boot6 run.scm — build seed-kernel ELF with tcc3.
     66 ;; Generated by bootprep/boot6-gen-runscm.sh; reads use in/, writes out/.
     67 
     68 (define (must r tag)
     69   (if (and (car r) (= 0 (cdr r)))
     70       r
     71       (begin
     72         (write-string stderr "boot6: step failed: ")
     73         (write-string stderr tag)
     74         (write-string stderr "\n")
     75         (exit 1))))
     76 
     77 (write-string stdout "boot6: tcc3 -c kernel.S\n")
     78 (must (run "in/tcc3" $KCFLAGS "-c" "-o" "out/kernel-asm.o" "in/kernel.S")
     79       "kernel.S -> kernel-asm.o")
     80 
     81 (write-string stdout "boot6: tcc3 -c kernel.c\n")
     82 (must (run "in/tcc3" $KCFLAGS "-Iin" "-c" "-o" "out/kernel.o" "in/kernel.c")
     83       "kernel.c -> kernel.o")
     84 
     85 (write-string stdout "boot6: tcc3 -c mmu.c\n")
     86 (must (run "in/tcc3" $KCFLAGS "-Iin" "-c" "-o" "out/mmu.o" "in/mmu.c")
     87       "mmu.c -> mmu.o")
     88 
     89 (write-string stdout "boot6: tcc3 -c mem.c\n")
     90 (must (run "in/tcc3" $KCFLAGS "-c" "-o" "out/mem.o" "in/mem.c")
     91       "mem.c -> mem.o")
     92 
     93 (write-string stdout "boot6: tcc3 link $OUT_FILE\n")
     94 (must (run "in/tcc3" "-nostdlib" "-static"
     95            "-Wl,-Ttext=$TTEXT"
     96            $LINK_OFORMAT
     97            "-o" "out/$OUT_FILE"
     98            "out/kernel-asm.o" "out/kernel.o" "out/mmu.o" "out/mem.o")
     99       "link $OUT_FILE")
    100 
    101 (write-string stdout "boot6: ALL-OK\n")
    102 (exit 0)
    103 EOF