GRUB2 EFI Support

GRUB2 EFI SupportFinnbarr P. Murphy

(fpm@fpmurphy.com)

Most GNU/Linux distributions utilize GNU GRUB (GRand Unified Bootloader) to boot the Linuxkernel. GRUB was conceived and initially developed by Erich Boleyn. It became part of the GNUproject in 1999 but was never officially released. The last development snapshot was v0.97 whichwas released in 2005. In spite of the fact that it was never officially released, it is used on millionsof computers worldwide.

The v0.97 codebase is now known as GRUB Legacy. Supposedly it is still in maintenance mode butno fixes have occurred in the last few years. As a result, vendors such as Red Hat maintain theirown branches of GRUB Legacy. Currently the Fedora Project applies 25 patches to the v0.97release of which 7 or 8 patches relate to the addition of EFI support. Other forks of GRUB Legacyinclude the bootloader used by Oracle to boot Solaris on IA32 and X64 platforms.

Many years ago the GRUB developers decided that a complete rewrite was required. The goal wasto make a more robust, portable and powerful version of GRUB which has support for a scriptinglanguage, internationalization and localization. GRUB 2 is derived from PUPA which was aresearch project funded by the Information-technology Promotion Agency of Japan to investigatethe next generation of GRUB.

For some time, I have been EFI-booting one of my X64 systems which runs Fedora 12 andexperimenting with the TianoCore EFI shell and various EFI utilities. The system boots into an EFIshell and I then use Fedora’s EFI-enabled version of GRUB Legacy to boot into various Fedorakernels.

Recently I decided to download the latest version of the GRUB 2 sources (currently v1.98), buildGRUB2 as an X64 EFI image and install it in parallel with the GRUB Legacy bootloader on the ESP(EFI System Partition) so that I could experiment with the new facilities available in the GRUB2bootloader.

Building the EFI version of GRUB2 was not an issue. As usual, the first requirement is to configurethe build. Here is a copy of the configuration options I choose:

$ ./configure --with-platform=efi --enable-grub-fstest=no--enable-grub-mkfont=no --disable-nls --enable-efiemu=no

As you can see I disabled EFI emulation, NLS support and various debugging utilities (fstest andmkfont.) The Makefile includes ../conf/x86_64-efi.mk which is where most of the build is specified.The default Makefile has a dependency on Ruby but this is easily worked around. The header../include/grub/i18n also has a minor error. The fix is to change the syntax of the ENABLE_NLSguard from #if to #ifdef.

After you have successfully run make, you have to generate the grub.efi image using thegrub-mkimage utility.

$ ./grub-mkimage -d . -o grub.efi boot linux part_gpt \ fat ext2 normal sh configfile lspci ls reboot datetime loadenv search lvm help quit

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GRUB2 EFI Support

GRUB2 is a very modular bootloader. You can include whichever modules you need into the imageusing grub-mkimage or you can load them from the GRUB2 shell. The boot module is mandatory,the linux module is the loader for Linux images, the help module displays help information, andthe remaining modules, except for quit are explained in Erich Boleyn’s commands summary page.

Here is a list of the modules which were built:

acpi.mod efi_gop.mod gcry_whirlpool.mod mmap.mod scsi.modaffs.mod efi_uga.mod gettext.mod msdospart.mod search_fs_file.modafs_be.mod elf.mod gfxmenu.mod multiboot2.mod search_fs_uuid.modafs.mod ext2.mod gfxterm.mod multiboot.mod search_label.modappleldr.mod extcmd.mod gptsync.mod normal.mod search.modata.mod fat.mod gzio.mod ntfscomp.mod setjmp.modat_keyboard.mod fixvideo.mod halt.mod ntfs.mod setpci.modbefs_be.mod font.mod handler.mod part_acorn.mod sfs.modbefs.mod fshelp.mod hashsum.mod part_amiga.mod sh.modbitmap.mod functional_test.mod help.mod part_apple.mod sleep.modbitmap_scale.mod gcry_arcfour.mod hexdump.mod part_gpt.mod tar.modblocklist.mod gcry_blowfish.mod hfs.mod part_msdos.mod terminal.modboot.mod gcry_camellia.mod hfsplus.mod part_sun.mod terminfo.modbufio.mod gcry_cast5.mod iso9660.mod parttool.mod test.modcat.mod gcry_crc.mod jfs.mod password.mod tga.modchain.mod gcry_des.mod jpeg.mod password_pbkdf2.mod trig.modcharset.mod gcry_md4.mod keystatus.mod pbkdf2.mod true.modcmp.mod gcry_md5.mod linux.mod pci.mod udf.modconfigfile.mod gcry_rfc2268.mod loadbios.mod png.mod ufs1.modcpio.mod gcry_rijndael.mod loadenv.mod probe.mod ufs2.modcpuid.mod gcry_rmd160.mod loopback.mod quit.mod vga_text.modcrc.mod gcry_seed.mod ls.mod raid5rec.mod video_fb.modcrypto.mod gcry_serpent.mod lspci.mod raid6rec.mod video.moddatehook.mod gcry_sha1.mod lvm.mod raid.mod videotest.moddate.mod gcry_sha256.mod mdraid.mod read.mod xfs.moddatetime.mod gcry_sha512.mod memrw.mod reboot.mod xnu.moddm_nv.mod gcry_tiger.mod minicmd.mod reiserfs.mod xnu_uuid.modecho.mod gcry_twofish.mod minix.mod relocator.mod

After building the grub.efi image I moved it to its home on the ESP and created a very basicGRUB2 configuration file which must be called grub.cfg. Here is a copy of my initial grub.cfg

# FPM 3/18/10 manual edittimeout=10default=0set color_normal=yellow/blueset color_highlight=blue/yellowmenuentry "Fedora 12" { root=(hd0,2) linux /vmlinuz-2.6.32.9-70.fc12.x86_64 ro root=/dev/mapper/vg_ultra-lv_root LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet nolapic initrd /initramfs-2.6.32.9-70.fc12.x86_64.img}

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GRUB2 EFI Support

Stanzas are phrased slightly differently and cannot be copied directly from a GRUB Legacyconfiguration file. They are pretty close though and no explanation of the required changes shouldbe necessary. Note that the command kernel has been superseded by linux. Note also that GRUB2partition numbers start at 1 not 0 but drives still start at 0. Thus the second partition of the firstdrive is hd(0,2) in GRUB2 but (hd0,1) in GRUB Legacy.

When I switched to GRUB2 to experiment using it to EFI-boot Fedora 12, I immediately noticedthat the time from when I hit the Enter key until I saw a Plymouth theme went from about 10second to over 3 minutes. It took me a while to track down the cause of this delay as the GRUB2codebase is significantly larger and more complex than the GRUB Legacy codebase andEFI-related code is in numerous subdirectories.

After a number of false starts, I finally tracked the issue down to the size of the disk cache. Seethe caching algorithm in get_disk_read() in the source file ../kern/disk.c. I probably could havebypassed the disk cache altogether, but found that increasing the cache size from 8 sectors to8192 sectors reduced the time to read the kernel and initrd image files to less than a few seconds.Here are the changes to make in ../include/grub/disk.h.

/* The size of a disk cache in sector units. */#ifdef GRUB_MACHINE_EFI#define GRUB_DISK_CACHE_SIZE 8192#define GRUB_DISK_CACHE_BITS 13#else#define GRUB_DISK_CACHE_SIZE 8#define GRUB_DISK_CACHE_BITS 3#endif

Note that I used the guard GRUB_MACHINE_EFI to guard any EFI-specific code in commonsource files.

One useful feature of GRUB2 are the reboot and halt modules. You can use these modules to addmenu options to either reboot or halt your system or you invoke these commands from the GRUB2command line. For example. here is a reboot menu option.

menuentry "Reboot" { reboot}

Currently, no command is available to quit out of GRUB2 and go back to the EFI shell. For non-EFIplatforms this is not a useful option but for EFI-based platforms it provides great flexibility. Itherefore decided to develop such a command and used the source code for the reboot commandas my template. In case anybody else wants to create such a GRUB2 command, here are therelevant details.

Create a file named quit.c in the ../commands subdirectory of your build tree which contains thefollowing source code:

/* quit.c - command to return to EFI shell *//* * GRUB -- GRand Unified Bootloader * Copyright (C) 2005,2007,2008 Free Software Foundation, Inc. * * GRUB is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by

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GRUB2 EFI Support

* the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * GRUB is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with GRUB. If not, see <http://www.gnu.org/licenses/>. */#include <grub/dl.h>#include <grub/command.h>#include <grub/misc.h>#include <grub/i18n.h>#include <grub/term.h>#include <grub/efi/efi.h>#include <grub/efi/api.h>#include <grub/efi/console.h>static grub_err_tgrub_cmd_quit (grub_command_t cmd __attribute__ ((unused)), int argc __attribute__ ((unused)), char **args __attribute__ ((unused))){ grub_efi_simple_text_output_interface_t *o; static grub_uint8_t efi_console_stdcolor = GRUB_EFI_TEXT_ATTR (GRUB_EFI_YELLOW, GRUB_EFI_BACKGROUND_BLACK); o = grub_efi_system_table->con_out; efi_call_2 (o->set_attributes, o, efi_console_stdcolor); efi_call_1 (o->clear_screen, o); grub_exit (); return 0;}static grub_command_t cmd;GRUB_MOD_INIT(quit){ cmd = grub_register_command ("quit", grub_cmd_quit, 0, N_("Return to EFI shell."));}GRUB_MOD_FINI(quit){ grub_unregister_command (cmd);}

The contents of this file should be self-explanatory to an experienced programmer. The two efi_calls invoke the appropriate EFI protocol calls to set the screen text-mode foreground andbackground colors and clear the screen.

Next add the following make directives to ../conf/x86_64-efi.mk which is the EFI-specific Makefile:

# For quit.mod.quit_mod_SOURCES = commands/quit.cclean-module-quit.mod.1: rm -f quit.mod mod-quit.o mod-quit.c pre-quit.o quit_mod-commands_quit.o und-quit.lstCLEAN_MODULE_TARGETS += clean-module-quit.mod.1clean-module-quit.mod-symbol.1: rm -f def-quit.lstCLEAN_MODULE_TARGETS += clean-module-quit.mod-symbol.1DEFSYMFILES += def-quit.lstmostlyclean-module-quit.mod.1: rm -f quit_mod-commands_quit.dMOSTLYCLEAN_MODULE_TARGETS += mostlyclean-module-quit.mod.1

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GRUB2 EFI Support

UNDSYMFILES += und-quit.lstifneq ($(TARGET_APPLE_CC),1)quit.mod: pre-quit.o mod-quit.o $(TARGET_OBJ2ELF) -rm -f $@ $(TARGET_CC) $(quit_mod_LDFLAGS) $(TARGET_LDFLAGS) -Wl,-r,-d -o $@ pre-quit.o mod-quit.o if test ! -z "$(TARGET_OBJ2ELF)"; then ./$(TARGET_OBJ2ELF) $@ || (rm -f $@; exit 1); fi $(STRIP) --strip-unneeded -K grub_mod_init -K grub_mod_fini -K _grub_mod_init -K _grub_mod_fini -R .note -R .comment $@elsequit.mod: pre-quit.o mod-quit.o $(TARGET_OBJ2ELF) -rm -f $@ -rm -f $@.bin $(TARGET_CC) $(quit_mod_LDFLAGS) $(TARGET_LDFLAGS) -Wl,-r,-d -o $@.bin pre-quit.o mod-quit.o $(OBJCONV) -f$(TARGET_MODULE_FORMAT) -nr:_grub_mod_init:grub_mod_init -nr:_grub_mod_fini:grub_mod_fini -wd1106 -nu -nd $@.bin $@ -rm -f $@.binendifpre-quit.o: $(quit_mod_DEPENDENCIES) quit_mod-commands_quit.o -rm -f $@ $(TARGET_CC) $(quit_mod_LDFLAGS) $(TARGET_LDFLAGS) -Wl,-r,-d -o $@ quit_mod-commands_quit.omod-quit.o: mod-quit.c $(TARGET_CC) $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -c -o $@ $<mod-quit.c: $(builddir)/moddep.lst $(srcdir)/genmodsrc.sh sh $(srcdir)/genmodsrc.sh 'quit' $< > $@ || (rm -f $@; exit 1)ifneq ($(TARGET_APPLE_CC),1)def-quit.lst: pre-quit.o $(NM) -g --defined-only -P -p $< | sed 's/^\([^ ]*\).*/\1 quit/' > $@elsedef-quit.lst: pre-quit.o $(NM) -g -P -p $< | grep -E '^[a-zA-Z0-9_]* [TDS]' | sed 's/^\([^ ]*\).*/\1 quit/' > $@endifund-quit.lst: pre-quit.o echo 'quit' > $@ $(NM) -u -P -p $< | cut -f1 -d' ' >> $@quit_mod-commands_quit.o: commands/quit.c $(commands/quit.c_DEPENDENCIES) $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -MD -c -o $@ $<-include quit_mod-commands_quit.dclean-module-quit_mod-commands_quit-extra.1: rm -f cmd-quit_mod-commands_quit.lst fs-quit_mod-commands_quit.lst partmap-quit_mod-commands_quit.lst handler-quit_mod-commands_quit.lst parttool-quit_mod-commands_quit.lst video-quit_mod-commands_quit.lst terminal-quit_mod-commands_quit.lstCLEAN_MODULE_TARGETS += clean-module-quit_mod-commands_quit-extra.1COMMANDFILES += cmd-quit_mod-commands_quit.lstFSFILES += fs-quit_mod-commands_quit.lstPARTTOOLFILES += parttool-quit_mod-commands_quit.lstPARTMAPFILES += partmap-quit_mod-commands_quit.lstHANDLERFILES += handler-quit_mod-commands_quit.lstTERMINALFILES += terminal-quit_mod-commands_quit.lstVIDEOFILES += video-quit_mod-commands_quit.lstcmd-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) gencmdlist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/gencmdlist.sh quit > $@ || (rm -f $@; exit 1)fs-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) genfslist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/genfslist.sh quit > $@ || (rm -f $@; exit 1)parttool-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) genparttoollist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS)

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$(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/genparttoollist.sh quit > $@ || (rm -f $@; exit 1)partmap-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) genpartmaplist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/genpartmaplist.sh quit > $@ || (rm -f $@; exit 1)handler-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) genhandlerlist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/genhandlerlist.sh quit > $@ || (rm -f $@; exit 1)terminal-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) genterminallist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/genterminallist.sh quit > $@ || (rm -f $@; exit 1)video-quit_mod-commands_quit.lst: commands/quit.c $(commands/quit.c_DEPENDENCIES) genvideolist.sh set -e; $(TARGET_CC) -Icommands -I$(srcdir)/commands $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) $(quit_mod_CFLAGS) -E $< | sh $(srcdir)/genvideolist.sh quit > $@ || (rm -f $@; exit 1)quit_mod_CFLAGS = $(COMMON_CFLAGS)quit_mod_LDFLAGS = $(COMMON_LDFLAGS)

You should now be able to build quit.mod by invoking make quit.mod from the root of your GRUB2build tree. Then use the grub-mkimage utility to incorporate the quit module into your grub.efiimage. After placing the newly created grub.efi image in the ESP, you should be able to use thequit command from the GRUB2 shell or via a stanza in grub.cfg.

The current linux loader does not reset the screen text-mode foreground and background colors totheir defaults. For EFI shells these are yellow and black respectively. Instead the GRUB2foreground and background colors propagate onto text outputted by the loader module. Here arethe diffs to the loader file ../loader/i386/efi/linux.c to correct this problem and add informativemessages similar to those outputted by GRUB Legacy.

37a38,41> #include <grub/efi/console.h>> #include <grub/i386/vga_common.h>>>240a245,247> grub_printf("Trying to allocate %u pages for VMLINUZ\n",> (unsigned) prot_mode_pages);>608a616,622> /* set color colors to EFI default */> grub_efi_simple_text_output_interface_t *o;> static grub_uint8_t efi_console_standard_color = GRUB_EFI_TEXT_ATTR (GRUB_EFI_YELLOW, GRUB_EFI_BACKGROUND_BLACK);>> o = grub_efi_system_table->con_out;> efi_call_2 (o->set_attributes, o, efi_console_standard_color);>809c823,824< grub_printf (" [Linux-bzImage, setup=0x%x, size=0x%x]\n",--->> grub_printf ("[Linux-EFI, setup=0x%x, size=0x%x]\n",

Once I had GRUB2 up and running, I decided to look at how to support a full-screen backgroundimage. This is one of the areas where GRUB Legacy has major limitations. It only supports a

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background image with a maximum of 16 colors and a maximum resolution of 640×480.

To test support for a background image in GRUB2, l took a Fedora 12 background image andconverted it into TGA format using GIMP. Why TGA? No particular reason. I could have just aseasily used JPEG or PNG formats. I placed this image in the ESP GRUB2 subdirectory.

Next I needed to obtain a suitable glyph (font) file for displaying characters when in graphicsmode. GRUB2 uses PFF2 bitmap fonts. Rather than going to the trouble of creating my own PFF2file, I simply extracted the font file unicode.pf2 from the Debian grub-common_1.98 package.

Finally, as shown below, I modified grub.cfg to load and configure the appropriate modules anddisplay the background image.

## FPM 3/19/10#timeout=20default=0if loadfont /efi/grub2/unicode.pf2then set gfxmode="1024x768x32" set gfxpayload=keep insmod gfxterm insmod efi_gop terminal_output gfxterm terminal gfxtermfiuse_bg=truebackgound_image /efi/grub2/fedora.tgaset color_normal=yellow/blueset color_highlight=blue/yellowmenuentry "Fedora 12" { root=(hd0,2) linux /vmlinuz-2.6.32.9-70.fc12.x86_64 ro root=/dev/mapper/vg_ultra-lv_root LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet nolapic initrd /initramfs-2.6.32.9-70.fc12.x86_64.img}menuentry "Reboot" { reboot}menuentry "Exit to EFI Shell" { quit}

You will notice that GRUB2 supports a rudimentary scripting language. Here I test that the fontfile /efi/grud2/unicode.pf2 is loaded before the gfxterm and efi_gop modules are loaded andconfigured. When I rebooted the system and invoked GRUB2 from the EFI shell, the specifiedFedora backgound image covered the whole screen without a border and characters werecorrectly displayed.

Is GRUB2 a viable option for EFI-booting Fedora 12 at this time? Yes, provided that it is modifiedto minimize the load delay caused by the default small disk caches. Do I like GRUB2? Yes. ActuallyI love the flexibility and additional functionality it provides. Broadening the question further, isGRUB2 ready for primetime use and should Fedora switch to GRUB2 in the near future? TheUbuntu, Gentoo and Debian distributions of GNU/Linux certainly think so and their latest releasesutilize it as the default bootloader. My answer to both questions is probably no. I personally thinkGRUB2 requires some work to harden the product – especially for EFI-booting. Other reasonsinclude a lack of accurate, up-to-date and complete end-user documentation and an over-complexproduct. By over-complex product, I mean the large number of modules and other files. Many of

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the modules, for example minix.mod, are of no use to users of Fedora on an IA32 or X64 platformand should not be distributed as part of a Fedora RPM.

There is a GRUB2 RPM available for Fedora 12. However it contains all the available loadablemodules irrespective of whether they are of any use to Fedora users. Worse still, it installs all themodules under /usr/lib/grub2/i386-pc/. Why not just put them under /usr/lib/grub2? What valuedoes the extra i386-pc add? I am on an x86-64 platform; I do not expect to find modules that Ineed in a directory called i386-pc. Yes, I understand that the GRUB2 boatloader always uses 32-bitmodules but that fact does not need to be embedded in a subdirectory name. In addition, twoimportant files are missing from the RPM, i.e. the font files unicode.pf2 and ascii.pf2. Withoutthese files, background images are not possible.

Should Fedora switch to using GRUB2 in the long term? Certainly. The extra features such asloadable modules, scripting and localization support are frankly very compelling.

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