RISC-V交叉编译链接错误：undefined reference to fseek/fread

问题描述 #

在VMware Ubuntu 22.04环境下使用riscv64-linux-gnu交叉编译工具链时，遇到以下链接错误：

riscv64-linux-gnu-ld: loader.c:(.text.naive_uload+0x4c): undefined reference to fseek' riscv64-linux-gnu-ld: loader.c:(.text.naive_uload+0x78): undefined reference to fread'
riscv64-linux-gnu-ld: loader.c:(.text.naive_uload+0xbc): undefined reference to fseek' riscv64-linux-gnu-ld: loader.c:(.text.naive_uload+0xe0): undefined reference to fread'

相关Makefile代码 #

主Makefile #

# Makefile for AbstractMachine Kernels and Libraries

### *Get a more readable version of this Makefile* by `make html` (requires python-markdown)
html:
    cat Makefile | sed 's/^\([^#]\)/    \1/g' | markdown_py > Makefile.html
.PHONY: html

## 1. Basic Setup and Checks

### Default to create a bare-metal kernel image
ifeq ($(MAKECMDGOALS),)
  MAKECMDGOALS  = image
  .DEFAULT_GOAL = image
endif

### Override checks when `make clean/clean-all/html`
ifeq ($(findstring $(MAKECMDGOALS),clean|clean-all|html),)

### Print build info message
$(info # Building $(NAME)-$(MAKECMDGOALS) [$(ARCH)])

### Check: environment variable `$AM_HOME` looks sane
ifeq ($(wildcard $(AM_HOME)/am/include/am.h),)
  $(error $$AM_HOME must be an AbstractMachine repo)
endif

### Check: environment variable `$ARCH` must be in the supported list
ARCHS = $(basename $(notdir $(shell ls $(AM_HOME)/scripts/*.mk)))
ifeq ($(filter $(ARCHS), $(ARCH)), )
  $(error Expected $$ARCH in {$(ARCHS)}, Got "$(ARCH)")
endif

### Extract instruction set architecture (`ISA`) and platform from `$ARCH`. Example: `ARCH=x86_64-qemu -> ISA=x86_64; PLATFORM=qemu`
ARCH_SPLIT = $(subst -, ,$(ARCH))
ISA        = $(word 1,$(ARCH_SPLIT))
PLATFORM   = $(word 2,$(ARCH_SPLIT))

### Check if there is something to build
ifeq ($(flavor SRCS), undefined)
  $(error Nothing to build)
endif

### Checks end here
endif

## 2. General Compilation Targets

### Create the destination directory (`build/$ARCH`)
WORK_DIR  = $(shell pwd)
DST_DIR   = $(WORK_DIR)/build/$(ARCH)
$(shell mkdir -p $(DST_DIR))

### Compilation targets (a binary image or archive)
IMAGE_REL = build/$(NAME)-$(ARCH)
IMAGE     = $(abspath $(IMAGE_REL))
ARCHIVE   = $(WORK_DIR)/build/$(NAME)-$(ARCH).a

### Collect the files to be linked: object files (`.o`) and libraries (`.a`)
OBJS      = $(addprefix $(DST_DIR)/, $(addsuffix .o, $(basename $(SRCS))))
LIBS     := $(sort $(LIBS) am klib) # lazy evaluation ("=") causes infinite recursions
LINKAGE   = $(OBJS) \
  $(addsuffix -$(ARCH).a, $(join \
    $(addsuffix /build/, $(addprefix $(AM_HOME)/, $(LIBS))), \
    $(LIBS) ))

## 3. General Compilation Flags

### (Cross) compilers, e.g., mips-linux-gnu-g++
AS        = $(CROSS_COMPILE)gcc
CC        = $(CROSS_COMPILE)gcc
CXX       = $(CROSS_COMPILE)g++
LD        = $(CROSS_COMPILE)ld
OBJDUMP   = $(CROSS_COMPILE)objdump
OBJCOPY   = $(CROSS_COMPILE)objcopy
READELF   = $(CROSS_COMPILE)readelf

### Compilation flags
INC_PATH += $(WORK_DIR)/include $(addsuffix /include/, $(addprefix $(AM_HOME)/, $(LIBS)))
INCFLAGS += $(addprefix -I, $(INC_PATH))

CFLAGS   += -O2 -MMD -Wall -Werror $(INCFLAGS) \
            -D__ISA__=\"$(ISA)\" -D__ISA_$(shell echo $(ISA) | tr a-z A-Z)__ \
            -D__ARCH__=$(ARCH) -D__ARCH_$(shell echo $(ARCH) | tr a-z A-Z | tr - _) \
            -D__PLATFORM__=$(PLATFORM) -D__PLATFORM_$(shell echo $(PLATFORM) | tr a-z A-Z | tr - _) \
            -DARCH_H=\"arch/$(ARCH).h\" \
            -fno-asynchronous-unwind-tables -fno-builtin -fno-stack-protector \
            -Wno-main -U_FORTIFY_SOURCE
CXXFLAGS +=  $(CFLAGS) -ffreestanding -fno-rtti -fno-exceptions
ASFLAGS  += -MMD $(INCFLAGS)
LDFLAGS  += -z noexecstack

## 4. Arch-Specific Configurations

### Paste in arch-specific configurations (e.g., from `scripts/x86_64-qemu.mk`)
-include $(AM_HOME)/scripts/$(ARCH).mk

### Fall back to native gcc/binutils if there is no cross compiler
ifeq ($(wildcard $(shell which $(CC))),)
  $(info #  $(CC) not found; fall back to default gcc and binutils)
  CROSS_COMPILE :=
endif

## 5. Compilation Rules

### Rule (compile): a single `.c` -> `.o` (gcc)
$(DST_DIR)/%.o: %.c
    @mkdir -p $(dir $@) && echo + CC $<
    @$(CC) -std=gnu11 $(CFLAGS) -c -o $@ $(realpath $<)

### Rule (compile): a single `.cc` -> `.o` (g++)
$(DST_DIR)/%.o: %.cc
    @mkdir -p $(dir $@) && echo + CXX $<
    @$(CXX) -std=c++17 $(CXXFLAGS) -c -o $@ $(realpath $<)

### Rule (compile): a single `.cpp` -> `.o` (g++)
$(DST_DIR)/%.o: %.cpp
    @mkdir -p $(dir $@) && echo + CXX $<
    @$(CXX) -std=c++17 $(CXXFLAGS) -c -o $@ $(realpath $<)

### Rule (compile): a single `.S` -> `.o` (gcc, which preprocesses and calls as)
$(DST_DIR)/%.o: %.S
    @mkdir -p $(dir $@) && echo + AS $<
    @$(AS) $(ASFLAGS) -c -o $@ $(realpath $<)

### Rule (recursive make): build a dependent library (am, klib, ...)
$(LIBS): %:
    @$(MAKE) -s -C $(AM_HOME)/$* archive

### Rule (link): objects (`*.o`) and libraries (`*.a`) -> `IMAGE.elf`, the final ELF binary to be packed into image (ld)
$(IMAGE).elf: $(OBJS) am $(LIBS)
    @echo + LD "->" $(IMAGE_REL).elf
    @$(LD) $(LDFLAGS) -o $(IMAGE).elf --start-group $(LINKAGE) --end-group

### Rule (archive): objects (`*.o`) -> `ARCHIVE.a` (ar)
$(ARCHIVE): $(OBJS)
    @echo + AR "->" $(shell realpath $@ --relative-to .)
    @ar rcs $(ARCHIVE) $(OBJS)

### Rule (`#include` dependencies): paste in `.d` files generated by gcc on `-MMD`
-include $(addprefix $(DST_DIR)/, $(addsuffix .d, $(basename $(SRCS))))

## 6. Miscellaneous

### Build order control
image: image-dep
archive: $(ARCHIVE)
image-dep: $(OBJS) am $(LIBS)
    @echo \# Creating image [$(ARCH)]
.PHONY: image image-dep archive run $(LIBS)

### Clean a single project (remove `build/`)
clean:
    rm -rf Makefile.html $(WORK_DIR)/build/
.PHONY: clean

### Clean all sub-projects within depth 2 (and ignore errors)
CLEAN_ALL = $(dir $(shell find . -mindepth 2 -name Makefile))
clean-all: $(CLEAN_ALL) clean
$(CLEAN_ALL):
    -@$(MAKE) -s -C $@ clean
.PHONY: clean-all $(CLEAN_ALL)

项目Makefile #

#HAS_NAVY = 1
RAMDISK_FILE = build/ramdisk.img

NAME = nanos-lite
SRCS = $(shell find -L ./src/ -name "*.c" -o -name "*.cpp" -o -name "*.S")
include $(AM_HOME)/Makefile

ifeq ($(ARCH),native)
ISA = am_native
else
INC_PATH += include $(NAVY_HOME)/libs/libc/include
endif

./src/resources.S: $(RAMDISK_FILE)
    @touch $@

ifeq ($(HAS_NAVY),)
files = $(RAMDISK_FILE) src/files.h src/syscall.h
# create an empty file if it does not exist
$(foreach f,$(files),$(if $(wildcard $f),, $(shell touch $f)))
else

ifeq ($(wildcard $(NAVY_HOME)/libs/libos/src/syscall.h),)
  $(error $$NAVY_HOME must be a Navy-apps repo)
endif

update:
    $(MAKE) -s -C $(NAVY_HOME) ISA=$(ISA) ramdisk
    @ln -sf $(NAVY_HOME)/build/ramdisk.img $(RAMDISK_FILE)
    @ln -sf $(NAVY_HOME)/build/ramdisk.h src/files.h
    @ln -sf $(NAVY_HOME)/libs/libos/src/syscall.h src/syscall.h

.PHONY: update
endif

解决方案 #

错误原因是链接阶段未包含实现fseek/fread的标准C库或项目自带的libc库，以下是几种可行的修复方式：

方式1：链接项目自带的NAVY libc #

取消项目Makefile中#HAS_NAVY = 1的注释，启用NAVY环境：

HAS_NAVY = 1

启用后，Makefile会自动链接NAVY的libc库，同时确保NAVY_HOME环境变量正确指向Navy-apps仓库路径。

方式2：在主Makefile中添加libc到链接库列表 #

修改主Makefile中的LIBS定义，加入libc：

LIBS     := $(sort $(LIBS) am klib libc)

这会让Makefile自动编译并链接AM_HOME或NAVY_HOME下的libc库。

方式3：直接链接交叉编译工具链的标准libc #

在主Makefile的LDFLAGS中添加-lc参数，强制链接riscv64-linux-gnu工具链的标准C库：

LDFLAGS  += -z noexecstack -lc

方式4：改用gcc而非ld进行链接 #

当前链接命令使用ld直接链接，而gcc会自动处理标准库的依赖和路径。修改主Makefile中的链接规则，将$(LD)替换为$(CC)：

$(IMAGE).elf: $(OBJS) am $(LIBS)
    @echo + LD "->" $(IMAGE_REL).elf
    @$(CC) $(LDFLAGS) -o $(IMAGE).elf --start-group $(LINKAGE) --end-group

内容的提问来源于stack exchange，提问作者Lonely George