#735 move cbfs creation to libreboot

CAR bootblock is most likely fixing a lot of the issues here, decreasing amount of binaries that need to be located at exact offset to bootblock (not checked).
Moving cbfs creation to libreboot would lower the space required, accelerate the build process, and decrease cost of adding new board to about 128KiB or less.
When libreboot would save individual binaries instead of entire image, it's important to check contents of cbfs generated by coreboot system, and in case libreboot didn't save a copy of everything - throw an error.

This will also need to be added/used as project inside libreboot build system, so image creation is saner and more flexible (like several payloads, or other data types). It will also make it more clean to add EC images, when shared on flash with host firmware, though one caveat to think about would be targets that don't use coreboot at all.

if you look at the comments in x86/memlayout.ld, cbfstool needs some magic for XIP to work

readelf -h build/cbfs/fallback/*.elf

File: build/cbfs/fallback/bootblock.elf
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0xfffffff0
  Start of program headers:          52 (bytes into file)
  Start of section headers:          83248 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         1
  Size of section headers:           40 (bytes)
  Number of section headers:         11
  Section header string table index: 10

File: build/cbfs/fallback/bootblock.raw.elf
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0xfffffff0
  Start of program headers:          52 (bytes into file)
  Start of section headers:          83248 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         1
  Size of section headers:           40 (bytes)
  Number of section headers:         11
  Section header string table index: 10

File: build/cbfs/fallback/postcar.elf
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0x2000000
  Start of program headers:          372 (bytes into file)
  Start of section headers:          52 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         1
  Size of section headers:           40 (bytes)
  Number of section headers:         8
  Section header string table index: 1

File: build/cbfs/fallback/ramstage.elf
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0xe00000
  Start of program headers:          372 (bytes into file)
  Start of section headers:          52 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         1
  Size of section headers:           40 (bytes)
  Number of section headers:         8
  Section header string table index: 1

File: build/cbfs/fallback/romstage.elf
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0x2000000
  Start of program headers:          52 (bytes into file)
  Start of section headers:          83452 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         1
  Size of section headers:           40 (bytes)
  Number of section headers:         8
  Section header string table index: 7

Current coreboot cbfs assembly examples (/Makefile.inc)

seavgabios.bin from path in CONFIG_PAYLOAD_VGABIOS_FILE

cbfs-files-$(CONFIG_SEABIOS_VGA_COREBOOT) += vgaroms/seavgabios.bin
vgaroms/seavgabios.bin-file := $(CONFIG_PAYLOAD_VGABIOS_FILE)
vgaroms/seavgabios.bin-type := raw

ramstage stage with compression: none/LZMA

cbfs-files-$(CONFIG_HAVE_RAMSTAGE) += $(CONFIG_CBFS_PREFIX)/ramstage
$(CONFIG_CBFS_PREFIX)/ramstage-file := $(RAMSTAGE)
$(CONFIG_CBFS_PREFIX)/ramstage-type := stage
$(CONFIG_CBFS_PREFIX)/ramstage-compression := $(CBFS_COMPRESS_FLAG)

Furthermore /Makefile.inc includes /site-local dir unconditionally, intended for eg. coreboot distro. Paper can generate /site-local/Makefile.inc with cbfs-files-y and place it there

Paper solutions

Short term: Use /site-local/Makefile.inc

In long term investigate possible choices of implementation:

• stripping out only those relevant cbfs-files* lines for given target and somehow using that directly with make
• building sample image without payload and extracting all files, while keeping track of their type, compression and potentially offset. A script in release tarball would then assemble desired configuration of an image based on those files + payload + flash size + any extra config. Alternatively paper just generates every possible configuration, but with more targets being added that might end up not being sustainable.