memtest86+ EFI » GDB debug script for memtest86+

Hint:

gcc -g -O0 Hello.c

objcopy --only-keep-debug kernel.elf kernel.debug
objcopy --strip kernel.elf

When efi executable is created from elf shared objectfile, only limited set of sections are copied into resulted image:
.text .sdata .data .dynamic .dynsym .rel .rela.reloc

If compile with "-ggdb" option, additional symbols .debug_info .debug_abbrev .debug_loc .debug_ranges .debug_line .debug_macinfo .debug_str but that does not launch in EFI Firmware

Actually you just need to run objcopy utility twice with different set of sections to copy and different output files

try:
CpuDeadLoop(void) {

volatile int Index;

for(Index=0; Index==0; ) {
    asm volatile("pause");
  }

}

This minimal example/setup creates a working hello.efi binary:

hello.c

#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;
}

Makefile

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

OBJS        = hello.o
TARGET        = hello.efi

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

CFLAGS        = $(EFFINCS) -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) $(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) $^ $@

This is a working example. The Makefile creates an efi-file without debug symbols and a debug-file with debug symbols.

hello.c:

#include <efi.h>
#include <efilib.h>

EFI_STATUS
EFIAPI
efi_main (EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable) {

    EFI_LOADED_IMAGE *loaded_image = NULL;
    EFI_STATUS status;

    InitializeLib(ImageHandle, SystemTable);
    Print(L"Hello, world!\n");

    status = uefi_call_wrapper(SystemTable->BootServices->HandleProtocol,
                    3,
                    ImageHandle,
                    &LoadedImageProtocol,
                    (void **)&loaded_image);

    if (EFI_ERROR(status)) {
        Print(L"handleprotocol: %r\n", status);
    }

    Print(L"Image base: 0x%lx\n", loaded_image->ImageBase);

    DEBUG((D_ERROR, "AllocatePool: out of pool  %x\n", status));

    volatile int wait = 1;
    while(wait) {
        __asm__ __volatile__("pause");
    }

    return EFI_SUCCESS;
}

Makefile:

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

OBJS        = hello.o
TARGET        = hello.efi
TARGET_DEBUG    = hello.debug

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

CFLAGS        = $(EFFINCS) -fno-stack-protector -fpic \
            -fshort-wchar -mno-red-zone -Wall
CFLAGS        +=    -ggdb3 -O0 -DDEBUG -DEFI_DEBUG=1

ifeq ($(ARCH),x86_64)
    CFLAGS += -DEFI_FUNCTION_WRAPPER
endif

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

SECTIONS    = .text .sdata .data .dynamic .dynsym .rel .rela .reloc

DEBUG_SECTIONS    = .debug_info .debug_abbrev .debug_aranges \
          .debug_line .debug_str

all: clear $(TARGET) $(TARGET_DEBUG)
    cp hello.efi ../test_code/hda-contents/

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

%.efi: %.so
    objcopy $(foreach sec,$(SECTIONS),-j $(sec)) \
    --target=efi-app-$(ARCH) $^ $@

%.debug: %.so
    objcopy $(foreach sec,$(SECTIONS) $(DEBUG_SECTIONS),-j $(sec)) \
    --target=efi-app-$(ARCH) $^ $@

clear:
    rm -f *.efi
    rm -f *.debug
    rm -f *.o
    rm -f *.so

ImageBase is output from hello.efi
Via

(gdb) file hello.efi
(gdb) info files
(gdb) file

Symbol-file can be loaded via

(gdb) add-symbol-file /path/to/debug/file/hello.debug (ImageBase + text-offset) -s .data (ImageBase + data-offset)