i will try to keep this as short as possible.
I created an UEFI application which uses just a simple malloc but it never returns from the call:
main.c:
#include <efi.h>
#include <efilib.h>
#include <stdlib.h>
EFI_STATUS
EFIAPI
efi_main (EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
{
InitializeLib(ImageHandle, SystemTable);
Print(L"trying to allocate memory\n");
malloc(16);
Print(L"allocated successfully\n");
return EFI_SUCCESS;
}
output:
trying to allocate memory
The system is a QEMU virtual machine under linux-ubuntu:
"qemu-system-x86_64 -cpu qemu64 -bios Bios/bios.bin -drive file=Bios/app.disk,format=raw -global isa-debugcon.iobase=0x402 -debugcon file:app.ovmf.log"
bios.bin is the UEFI firmware https://wiki.ubuntu.com/UEFI/OVMF.
main.efi is written to app.disk with
dd if=/dev/zero of=Bios/app.disk bs=1 count=1 seek=$(( (128 * 1024) - 1))
sudo mkfs.vfat Bios/app.disk
mkdir Bios/mnt_app
cp Bios/app.disk Bios/mnt_app
sudo mount Bios/app.disk Bios/mnt_app
sudo cp kernel/main.efi Bios/mnt_app
build process of main.c is almost complete copy paste from https://www.rodsbooks.com/efi-programming/hello.html:
ARCH = $(shell uname -m | sed s,i[3456789]86,ia32,)
OBJS = main.o
TARGET = main.efi
EFIINC = /usr/include/efi
EFIINCS = -I$(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 = $(EFIINCS) -fno-stack-protector -fpic \
-fshort-wchar -mno-red-zone -Wall
ifeq ($(ARCH),x86_64)
CFLAGS += -DEFI_FUNCTION_WRAPPER
endif
LDFLAGS = -nostdlib -znocombreloc -T $(EFI_LDS) -shared \
-Bsymbolic -L $(EFILIB) $(EFI_CRT_OBJS)
all: $(TARGET)
main.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) $^ $@
@echo done building target
for reasons i don't know, malloc is just not working and is probably not intended to be used - at least it seems like that. if you need dynamic memory allocation, create your own malloc with memory pools:
void * malloc(UINTN poolSize)
{
EFI_STATUS status;
void * handle;
Print(L"allocating memory pool\n");
status = uefi_call_wrapper(BS->AllocatePool, 3, EfiLoaderData, poolSize, &handle);
if(status == EFI_OUT_OF_RESOURCES)
{
Print(L"out of resources for pool\n");
return 0;
}
else if(status == EFI_INVALID_PARAMETER)
{
Print(L"invalid pool type\n");
return 0;
}
else
{
Print(L"memory pool successfully allocated\n");
return handle;
}
}
free equivalent:
void free(void * pool)
{
EFI_STATUS status;
Print(L"freeing memory pool\n");
status = uefi_call_wrapper(BS->FreePool, 1, pool);
if(status == EFI_INVALID_PARAMETER)
{
Print(L"invalid pool pointer\n");
}
else
{
Print(L"memory pool successfully freed\n");
}
}
use it like you would usually use malloc and free:
EFI_STATUS
EFIAPI
efi_main (EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
{
InitializeLib(ImageHandle, SystemTable);
void * memoryPointer = malloc(1024);
free(memoryPointer);
return EFI_SUCCESS;
}
output:
allocating memory pool
memory pool successfully allocated
freeing memory pool
memory pool successfully freed