efi.mk(3)

📦 version 3.0.11, in centos-stream 9

💅 efi.mk(3) — the group-chat guide

okay so bestie, welcome to efi.mk(3), straight out of the Library Functions Manual ✨ this whole page is literally about one makefile include that makes EFI binaries happen. buckle up 🎀

🌸 NAME 🌸

efi.mk — the makefile include that builds EFI binaries for you, no cap 👑

✨ SYNOPSIS ✨

include efi.mk

that's it. that's the whole vibe check. one line and you're in 🫶

💖 DESCRIPTION 💖

So the gnu-efi library ships a set of makefiles that produce EFI binaries on the supported platforms, plus a whole bunch of make variables you can set to control how each step gets built 🔥 You can set these in your makefile or on the command line — but ngl they're normally set to reasonable defaults already, so most of the time you're just gonna use the += operator (like in the EXAMPLES section below) rather than fully replacing them. Replacement is a whole thing; appending is the main character move 💅

🧚 make variables

  • EFI_ARCH_CFLAGS — architecture-specific gcc command line options for building a .efi.o 🦋
  • EFI_ARCH_LDFLAGS — architecture-specific ld command line options for building the .efi.so 🌈
  • EFI_ARCH_FORMAT — architecture-specific objcopy arguments for building the final .efi binary ⭐
  • CROSS_COMPILE — the compiler prefix for cross-compilation. like, for example, "aarch64-linux-gnu-" 💀
  • EFI_CC — the C compiler. defaults to either $(CROSS_COMPILE)gcc or $(CROSS_COMPILE)clang, depending on what $(CC) was set to when gnu-efi was built 🍓
  • EFI_HOSTCC — defaults to whatever $(CC) was set to when gnu-efi was built 👀
  • EFI_HOSTARCH — one of aa64, arm, ia32, ia64, x64, or mips64el, representing the EFI architecture name of the host machine during the build 🖥️
  • EFI_ARCH — one of aa64, arm, ia32, ia64, x64, or mips64el, representing the EFI architecture name of the target 🎯
  • EFI_BFDARCH — the architecture name for the BFD target for objcopy 🎀
  • EFI_ARCH_3264 — usually empty; if you're cross compiling, this will default to e.g. -m64 if you're building for an x64 target on an i686 host 🤯
  • EFI_CC_INCLUDES — the list of default include paths for the compiler, as a gcc command line argument. defaults to the output of $(EFI_CC) $(EFI_ARCH_3264) -print-file-name=include, for example /usr/lib/gcc/x86_64-redhat-linux/9/include. note that there is no -I prefix on these ⚠️
  • EFI_INCLUDES — the gnu-efi include paths. note that there is no -I prefix on these either 🙈
  • EFI_CPPFLAGS — flags passed to gcc regardless of the build target 💜
  • EFI_CFLAGS — flags passed to gcc for building any binary target. defaults to $(EFI_CPPFLAGS) $(EFI_ARCH_CFLAGS) 🔥
  • EFI_LDSCRIPT — the linker script passed to ld -T for linking .efi.so build targets. defaults to /usr/lib/gnuefi/$(EFI_ARCH)/efi.lds 📜
  • EFI_LIBGCC — the path to libgcc. defaults to the result of $(EFI_CC) $(EFI_ARCH_3264) -print-libgcc-file-name 🧚
  • EFI_LDFLAGS — other command line to pass to ld before object names. defaults to -nostdlib --warn-common --no-undefined --fatal-warnings --build-id=sha1 -shared -Bsymbolic -L/usr/lib/gnuefi/$(EFI_ARCH) /usr/lib/gnuefi/$(EFI_ARCH)/crt0.o 💅
  • EFI_CCLDFLAGS — normally derived from $(EFI_LDFLAGS) 🌸
  • EFI_LDLIBS — libraries to pass to ld after target object names. defaults to -lefi -lgnuefi $(EFI_LIBGCC) -T $(EFI_LDSCRIPT) 📚
  • EFI_CCLDLIBS — derived from $(EFI_LDLIBS) 🫶
  • EFI_ARFLAGS — flags to pass to ar to make a .efi.a target. defaults to "rDv" 🗃️
  • EFI_ASFLAGS — flags to pass to gcc to make a .efi.o object from a .S file ⚙️
  • EFI_OBJCOPY_FLAGS — flags to pass to objcopy to make a .efi binary target. defaults to --file-alignment 512 --section-alignment 4096 -D ✂️
  • EFI_BIN_SECTIONS — names of sections to go into .efi binary targets. if you have special sections, add them here 👑
  • EFI_DEBUG_SECTIONS — names of sections to go into .efi.debug targets. if you have special debug sections, add them here 🔍

🦋 the make rules

in addition, there are several make rules defined, which those variables affect as appropriate:

  • %.efi : %.efi.so — build a .efi binary ✨
  • %.efi.debug : %efi.so — build debuginfo 🐛
  • %.efi.so : — build the intermediate .efi.so to be linked as a .efi binary. add .o files as dependencies to a concrete .efi.so rule in order to define targets 🧩
  • %.efi.a : — build an intermediate archive file for linking into a .efi.so 📦
  • %.efi.o : %.c — build an object file from a .c file 💜
  • %.efi.o : %.S — build an object file from a .S file 💜
  • efi_clean : — remove all files in the current working directory with the suffixes .efi, .efi.a, .efi.debug, .efi.o, or .efi.so. the ultimate glow-up cleanse 🧼

🎀 EXAMPLES 🎀

ok so here's a simple makefile used to build an EFI binary named foo.efi from source files foo.c and bar.c 💖 It includes the special section .weird in the final binary, and the name of that is defined within the .c source files using the macro WEIRD_SECTION_NAME:

include efi.mk
all : foo.efi
%.efi.o : | EFI_CFLAGS+=-DWEIRD_SECTION_NAME=\".weird\"
foo.efi : | EFI_BIN_SECTIONS+=.weird
foo.efi.so : foo.efi.o bar.efi.o
clean : efi_clean

the following example shows how to cross-compile a binary for another architecture (in this case, ARM Aarch64, which EFI calls aa64). this assumes that you have the crt0.o, efi.lds, libgnuefi.a, and libefi.a files for Aarch64 installed in /usr/lib/gnuefi/aa64/ 🌍

$ make CROSS_COMPILE=aarch64-linux-gnu- EFI_ARCH=aa64 foo.efi

👑 AUTHORS 👑

Peter Jones <pjones@redhat.com> — thank you icon, we stan 🫶

and that's the whole page bestie, go forth and build some EFI binaries 💅✨

okay and for the cute sign-off — this page is dated Thu Nov 21 2019, and it's from the efi.mk(3) manual, so that's the source + version + date combo, mwah 🎀 bye!!

📦 where this page comes from