Can't link crt0-efi-x86_64.o to create an EFI application

[Donald A. Dade]

$ uname -a
Linux x6 4.4.0-59-generic #80-Ubuntu SMP Fri Jan 6 17:47:47 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release -rd
Description: Ubuntu 16.04.2 LTS
Release: 16.04

$ apt-cache policy gnu-efi
gnu-efi:
  Installed: 3.0.2-1ubuntu1
  Candidate: 3.0.2-1ubuntu1
  Version table:
 *** 3.0.2-1ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

$ make
ld -nostdlib -znocombreloc -T /usr/lib/elf_x86_64_efi.lds -shared -Bsymbolic -L /usr/lib -L /usr/lib /usr/lib/crt0-efi-x86_64.o main.o -o hello.so -lefi -lgnuefi
ld: /usr/lib/crt0-efi-x86_64.o: relocation R_X86_64_PC32 against undefined symbol `efi_main' can not be used when making a shared object; recompile with -fPIC

I expected the link to succeed, but it fails with the above error.

Sure enough, the object code has PC32 relocation records:

$ readelf -r /usr/lib/crt0-efi-x86_64.o
Relocation section '.rela.text' at offset 0x238 contains 4 entries:
  Offset Info Type Sym. Value Sym. Name + Addend
000000000009 000900000002 R_X86_64_PC32 0000000000000000 ImageBase - 4
000000000010 000a00000002 R_X86_64_PC32 0000000000000000 _DYNAMIC - 4
000000000019 000b00000002 R_X86_64_PC32 0000000000000000 _relocate - 4
000000000020 000c00000002 R_X86_64_PC32 0000000000000000 efi_main - 4

Relocation section '.rela.reloc' at offset 0x298 contains 1 entries:
  Offset Info Type Sym. Value Sym. Name + Addend
000000000000 000200000002 R_X86_64_PC32 0000000000000000 .data + 0

[Donald A. Dade (donald-dade)]

$ cat main.cpp
#include <efi.h>
#include <efilib.h>

EFI_STATUS
EFIAPI
efi_main (EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable) {
   InitializeLib(ImageHandle, SystemTable);
   Print(L"Hello, world!\n");

   return EFI_SUCCESS;
}

$ cat Makefile
ARCH = $(shell uname -m | sed s,i[3456789]86,ia32,)

OBJS = main.o
TARGET = hello.efi

EFIINC = /usr/include/efi
EFIINCS = -I$(EFIINC) -I$(EFIINC)/$(ARCH) -I$(EFIINC)/protocol
LIB = /usr/lib
EFILIB = /usr/lib
EFI_CRT_OBJS = $(EFILIB)/crt0-efi-$(ARCH).o
EFI_LDS = $(EFILIB)/elf_$(ARCH)_efi.lds

CXXFLAGS = $(EFIINCS) -fno-stack-protector -fpic \
                  -fshort-wchar -mno-red-zone -Wall
ifeq ($(ARCH),x86_64)
  CFLAGS += -DEFI_FUNCTION_WRAPPER
endif

LDFLAGS = -nostdlib -znocombreloc -T $(EFI_LDS) -shared \
                  -Bsymbolic -L $(EFILIB) -L $(LIB) $(EFI_CRT_OBJS)

all: $(TARGET)

hello.so: $(OBJS)
        ld $(LDFLAGS) $(OBJS) -o $@ -lefi -lgnuefi

%.efi: %.so
        objcopy -j .text -j .sdata -j .data -j .dynamic \
                -j .dynsym -j .rel -j .rela -j .reloc \
                --target=efi-app-$(ARCH) $^ $@

clean :
        rm -rf $(TARGET) $(OBJS)

realclean: clean

$ make
ld -nostdlib -znocombreloc -T /usr/lib/elf_x86_64_efi.lds -shared -Bsymbolic -L /usr/lib -L /usr/lib /usr/lib/crt0-efi-x86_64.o main.o -o hello.so -lefi -lgnuefi
ld: /usr/lib/crt0-efi-x86_64.o: relocation R_X86_64_PC32 against undefined symbol `efi_main' can not be used when making a shared object; recompile with -fPIC
ld: final link failed: Bad value
Makefile:25: recipe for target 'hello.so' failed
make: *** [hello.so] Error 1

[Donald A. Dade (donald-dade)]

Why does the library file crt0-efi-x86_64.o contain R_X86_64_PC32 relocation records, and not R_X86_64_PC64?