c - linux内核qemu执行make命令报错 "undefined reference to ` cprintf ''"

Question

(1) 这是主函数(runproctest.c):

#include "defs.h"

void
runproctest(void)
{
 cprintf("testing runnable: test1\n");
}

(2) defs.h:

// console.c
void            cprintf(char*, ...);

(3) 控制台.c

#include "defs.h"

void
cprintf(char *fmt, ...)
{
  int i, c, locking;
  uint *argp;
  char *s;

  locking = cons.locking;
  if(locking)
    acquire(&cons.lock);

  if (fmt == 0)
...
}

(4) 主.c

#include "types.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "mmu.h"
#include "proc.h"
#include "x86.h"

static void startothers(void);
static void mpmain(void)  __attribute__((noreturn));
extern pde_t *kpgdir;
extern char end[]; // first address after kernel loaded from ELF file

// Bootstrap processor starts running C code here.
// Allocate a real stack and switch to it, first
// doing some setup required for memory allocator to work.
int
main(void)
{
  kinit1(end, P2V(4*1024*1024)); // phys page allocator
  kvmalloc();      // kernel page table
  mpinit();        // detect other processors
  lapicinit();     // interrupt controller
  seginit();       // segment descriptors
  cprintf("\ncpu%d: starting xv6\n\n", cpunum());
  picinit();       // another interrupt controller
  ioapicinit();    // another interrupt controller
  consoleinit();   // console hardware
  uartinit();      // serial port
  pinit();         // process table
  tvinit();        // trap vectors
  binit();         // buffer cache
  fileinit();      // file table
  ideinit();       // disk
  if(!ismp)
    timerinit();   // uniprocessor timer
  startothers();   // start other processors
  kinit2(P2V(4*1024*1024), P2V(PHYSTOP)); // must come after startothers()
  userinit();      // first user process
  mpmain();        // finish this processor's setup
}

// Other CPUs jump here from entryother.S.
static void
mpenter(void)
{
  switchkvm();
  seginit();
  lapicinit();
  mpmain();
}

// Common CPU setup code.
static void
mpmain(void)
{
  cprintf("cpu%d: starting\n", cpunum());
  idtinit();       // load idt register
  xchg(&cpu->started, 1); // tell startothers() we're up
  scheduler();     // start running processes
}

pde_t entrypgdir[];  // For entry.S

// Start the non-boot (AP) processors.
static void
startothers(void)
{
  extern uchar _binary_entryother_start[], _binary_entryother_size[];
  uchar *code;
  struct cpu *c;
  char *stack;

  // Write entry code to unused memory at 0x7000.
  // The linker has placed the image of entryother.S in
  // _binary_entryother_start.
  code = P2V(0x7000);
  memmove(code, _binary_entryother_start, (uint)_binary_entryother_size);

  for(c = cpus; c < cpus+ncpu; c++){
    if(c == cpus+cpunum())  // We've started already.
      continue;

    // Tell entryother.S what stack to use, where to enter, and what
    // pgdir to use. We cannot use kpgdir yet, because the AP processor
    // is running in low  memory, so we use entrypgdir for the APs too.
    stack = kalloc();
    *(void**)(code-4) = stack + KSTACKSIZE;
    *(void**)(code-8) = mpenter;
    *(int**)(code-12) = (void *) V2P(entrypgdir);

    lapicstartap(c->apicid, V2P(code));

    // wait for cpu to finish mpmain()
    while(c->started == 0)
      ;
  }
}

// The boot page table used in entry.S and entryother.S.
// Page directories (and page tables) must start on page boundaries,
// hence the __aligned__ attribute.
// PTE_PS in a page directory entry enables 4Mbyte pages.

__attribute__((__aligned__(PGSIZE)))
pde_t entrypgdir[NPDENTRIES] = {
  // Map VA's [0, 4MB) to PA's [0, 4MB)
  [0] = (0) | PTE_P | PTE_W | PTE_PS,
  // Map VA's [KERNBASE, KERNBASE+4MB) to PA's [0, 4MB)
  [KERNBASE>>PDXSHIFT] = (0) | PTE_P | PTE_W | PTE_PS,
};

(5) 这是我的 Makefile:

OBJS = \
    bio.o\
    console.o\
    exec.o\
    file.o\
    fs.o\
    ide.o\
    ioapic.o\
    kalloc.o\
    kbd.o\
    lapic.o\
    log.o\
    main.o\
    mp.o\
    picirq.o\
    pipe.o\
    proc.o\
    spinlock.o\
    string.o\
    swtch.o\
    syscall.o\
    sysfile.o\
    sysproc.o\
    timer.o\
    trapasm.o\
    trap.o\
    uart.o\
    vectors.o\
    vm.o\
        runproctest.o\

# Cross-compiling (e.g., on Mac OS X)
# TOOLPREFIX = i386-jos-elf

# Using native tools (e.g., on X86 Linux)
#TOOLPREFIX = 

# Try to infer the correct TOOLPREFIX if not set
ifndef TOOLPREFIX
TOOLPREFIX := $(shell if i386-jos-elf-objdump -i 2>&1 | grep '^elf32-i386$$' >/dev/null 2>&1; \
    then echo 'i386-jos-elf-'; \
    elif objdump -i 2>&1 | grep 'elf32-i386' >/dev/null 2>&1; \
    then echo ''; \
    else echo "***" 1>&2; \
    echo "*** Error: Couldn't find an i386-*-elf version of GCC/binutils." 1>&2; \
    echo "*** Is the directory with i386-jos-elf-gcc in your PATH?" 1>&2; \
    echo "*** If your i386-*-elf toolchain is installed with a command" 1>&2; \
    echo "*** prefix other than 'i386-jos-elf-', set your TOOLPREFIX" 1>&2; \
    echo "*** environment variable to that prefix and run 'make' again." 1>&2; \
    echo "*** To turn off this error, run 'gmake TOOLPREFIX= ...'." 1>&2; \
    echo "***" 1>&2; exit 1; fi)
endif

# If the makefile can't find QEMU, specify its path here
 QEMU = /home/yuanzheng/Qemu_installed/bin/qemu-system-i386

# Try to infer the correct QEMU
ifndef QEMU
QEMU = $(shell if which qemu > /dev/null; \
    then echo qemu; exit; \
    elif which qemu-system-i386 > /dev/null; \
    then echo qemu-system-i386; exit; \
    else \
    qemu=/Applications/Q.app/Contents/MacOS/i386-softmmu.app/Contents/MacOS/i386-softmmu; \
    if test -x $$qemu; then echo $$qemu; exit; fi; fi; \
    echo "***" 1>&2; \
    echo "*** Error: Couldn't find a working QEMU executable." 1>&2; \
    echo "*** Is the directory containing the qemu binary in your PATH" 1>&2; \
    echo "*** or have you tried setting the QEMU variable in Makefile?" 1>&2; \
    echo "***" 1>&2; exit 1)
endif

CC = $(TOOLPREFIX)gcc
AS = $(TOOLPREFIX)gas
LD = $(TOOLPREFIX)ld
OBJCOPY = $(TOOLPREFIX)objcopy
OBJDUMP = $(TOOLPREFIX)objdump
CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
#CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -fvar-tracking -fvar-tracking-assignments -O0 -g -Wall -MD -gdwarf-2 -m32 -Werror -fno-omit-frame-pointer
CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
ASFLAGS = -m32 -gdwarf-2 -Wa,-divide
# FreeBSD ld wants ``elf_i386_fbsd''
LDFLAGS += -m $(shell $(LD) -V | grep elf_i386 2>/dev/null)

xv6.img: bootblock kernel fs.img
    dd if=/dev/zero of=xv6.img count=10000
    dd if=bootblock of=xv6.img conv=notrunc
    dd if=kernel of=xv6.img seek=1 conv=notrunc

xv6memfs.img: bootblock kernelmemfs
    dd if=/dev/zero of=xv6memfs.img count=10000
    dd if=bootblock of=xv6memfs.img conv=notrunc
    dd if=kernelmemfs of=xv6memfs.img seek=1 conv=notrunc

bootblock: bootasm.S bootmain.c
    $(CC) $(CFLAGS) -fno-pic -O -nostdinc -I. -c bootmain.c
    $(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c bootasm.S
    $(LD) $(LDFLAGS) -N -e start -Ttext 0x7C00 -o bootblock.o bootasm.o bootmain.o
    $(OBJDUMP) -S bootblock.o > bootblock.asm
    $(OBJCOPY) -S -O binary -j .text bootblock.o bootblock
    ./sign.pl bootblock

entryother: entryother.S
    $(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c entryother.S
    $(LD) $(LDFLAGS) -N -e start -Ttext 0x7000 -o bootblockother.o entryother.o
    $(OBJCOPY) -S -O binary -j .text bootblockother.o entryother
    $(OBJDUMP) -S bootblockother.o > entryother.asm

initcode: initcode.S
    $(CC) $(CFLAGS) -nostdinc -I. -c initcode.S
    $(LD) $(LDFLAGS) -N -e start -Ttext 0 -o initcode.out initcode.o
    $(OBJCOPY) -S -O binary initcode.out initcode
    $(OBJDUMP) -S initcode.o > initcode.asm

kernel: $(OBJS) entry.o entryother initcode kernel.ld
    $(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o $(OBJS) -b binary initcode entryother
    $(OBJDUMP) -S kernel > kernel.asm
    $(OBJDUMP) -t kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernel.sym

# kernelmemfs is a copy of kernel that maintains the
# disk image in memory instead of writing to a disk.
# This is not so useful for testing persistent storage or
# exploring disk buffering implementations, but it is
# great for testing the kernel on real hardware without
# needing a scratch disk.
MEMFSOBJS = $(filter-out ide.o,$(OBJS)) memide.o
kernelmemfs: $(MEMFSOBJS) entry.o entryother initcode kernel.ld fs.img
    $(LD) $(LDFLAGS) -T kernel.ld -o kernelmemfs entry.o  $(MEMFSOBJS) -b binary initcode entryother fs.img
    $(OBJDUMP) -S kernelmemfs > kernelmemfs.asm
    $(OBJDUMP) -t kernelmemfs | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernelmemfs.sym

tags: $(OBJS) entryother.S _init
    etags *.S *.c

vectors.S: vectors.pl
    perl vectors.pl > vectors.S

ULIB = ulib.o usys.o printf.o umalloc.o

_%: %.o $(ULIB)
    $(LD) $(LDFLAGS) -N -e main -Ttext 0 -o $@ $^
    $(OBJDUMP) -S $@ > $*.asm
    $(OBJDUMP) -t $@ | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > $*.sym

_forktest: forktest.o $(ULIB)
    # forktest has less library code linked in - needs to be small
    # in order to be able to max out the proc table.
    $(LD) $(LDFLAGS) -N -e main -Ttext 0 -o _forktest forktest.o ulib.o usys.o
    $(OBJDUMP) -S _forktest > forktest.asm

mkfs: mkfs.c fs.h
    gcc -Werror -Wall -o mkfs mkfs.c

# Prevent deletion of intermediate files, e.g. cat.o, after first build, so
# that disk image changes after first build are persistent until clean.  More
# details:
# http://www.gnu.org/software/make/manual/html_node/Chained-Rules.html
.PRECIOUS: %.o

UPROGS=\
    _cat\
    _echo\
    _forktest\
    _grep\
    _init\
    _kill\
    _ln\
    _ls\
    _mkdir\
    _rm\
    _sh\
    _stressfs\
    _usertests\
    _wc\
    _zombie\
        _runnable\
        _runnabletest\
        _runproctest\

fs.img: mkfs README $(UPROGS)
    ./mkfs fs.img README $(UPROGS)

-include *.d

clean: 
    rm -f *.tex *.dvi *.idx *.aux *.log *.ind *.ilg \
    *.o *.d *.asm *.sym vectors.S bootblock entryother \
    initcode initcode.out kernel xv6.img fs.img kernelmemfs mkfs \
    .gdbinit \
    $(UPROGS)

# make a printout
FILES = $(shell grep -v '^\#' runoff.list)
PRINT = runoff.list runoff.spec README toc.hdr toc.ftr $(FILES)

xv6.pdf: $(PRINT)
    ./runoff
    ls -l xv6.pdf

print: xv6.pdf

# run in emulators

bochs : fs.img xv6.img
    if [ ! -e .bochsrc ]; then ln -s dot-bochsrc .bochsrc; fi
    bochs -q

# try to generate a unique GDB port
GDBPORT = $(shell expr `id -u` % 5000 + 25000)
# QEMU's gdb stub command line changed in 0.11
QEMUGDB = $(shell if $(QEMU) -help | grep -q '^-gdb'; \
    then echo "-gdb tcp::$(GDBPORT)"; \
    else echo "-s -p $(GDBPORT)"; fi)
ifndef CPUS
CPUS := 2
endif
QEMUOPTS = -drive file=fs.img,index=1,media=disk,format=raw -drive file=xv6.img,index=0,media=disk,format=raw -smp $(CPUS) -m 512 $(QEMUEXTRA)

qemu: fs.img xv6.img
    $(QEMU) -serial mon:stdio $(QEMUOPTS)

qemu-memfs: xv6memfs.img
    $(QEMU) -drive file=xv6memfs.img,index=0,media=disk,format=raw -smp $(CPUS) -m 256

qemu-nox: fs.img xv6.img
    $(QEMU) -nographic $(QEMUOPTS)

.gdbinit: .gdbinit.tmpl
    sed "s/localhost:1234/localhost:$(GDBPORT)/" < $^ > $@

qemu-gdb: fs.img xv6.img .gdbinit
    @echo "*** Now run 'gdb'." 1>&2
    $(QEMU) -serial mon:stdio $(QEMUOPTS) -S $(QEMUGDB)

qemu-nox-gdb: fs.img xv6.img .gdbinit
    @echo "*** Now run 'gdb'." 1>&2
    $(QEMU) -nographic $(QEMUOPTS) -S $(QEMUGDB)

# CUT HERE
# prepare dist for students
# after running make dist, probably want to
# rename it to rev0 or rev1 or so on and then
# check in that version.

EXTRA=\
    mkfs.c ulib.c user.h cat.c echo.c forktest.c grep.c kill.c\
    ln.c ls.c mkdir.c rm.c stressfs.c usertests.c wc.c zombie.c\
    printf.c umalloc.c runnable.c printf.h runnabletest.c runproctest.c\
    README dot-bochsrc *.pl toc.* runoff runoff1 runoff.list\
    .gdbinit.tmpl gdbutil\

dist:
    rm -rf dist
    mkdir dist
    for i in $(FILES); \
    do \
        grep -v PAGEBREAK $$i >dist/$$i; \
    done
    sed '/CUT HERE/,$$d' Makefile >dist/Makefile
    echo >dist/runoff.spec
    cp $(EXTRA) dist

dist-test:
    rm -rf dist
    make dist
    rm -rf dist-test
    mkdir dist-test
    cp dist/* dist-test
    cd dist-test; $(MAKE) print
    cd dist-test; $(MAKE) bochs || true
    cd dist-test; $(MAKE) qemu

# update this rule (change rev#) when it is time to
# make a new revision.
tar:
    rm -rf /tmp/xv6
    mkdir -p /tmp/xv6
    cp dist/* dist/.gdbinit.tmpl /tmp/xv6
    (cd /tmp; tar cf - xv6) | gzip >xv6-rev9.tar.gz  # the next one will be 9 (6/27/15)

.PHONY: dist-test dist

当我输入 make qemu 时出现问题:

yuanzheng@ubuntu:~/Operating_System/xv6_sourcecode/xv6-public$ make qemu
ld -m    elf_i386 -N -e main -Ttext 0 -o _runproctest runproctest.o ulib.o usys.o printf.o umalloc.o
ld: warning: cannot find entry symbol main; defaulting to 0000000000000000
runproctest.o: In function `runproctest':
/home/yuanzheng/Operating_System/xv6_sourcecode/xv6-public/runproctest.c:26: undefined reference to `cprintf'
Makefile:141: recipe for target '_runproctest' failed
make: *** [_runproctest] Error 1

我不知道为什么会这样..

Answer 1

在 makefile 中，这一行:

ld -m    elf_i386 -N -e main -Ttext 0 -o _runproctest runproctest.o ulib.o usys.o printf.o umalloc.o

应该是:

ld -m    elf_i386 -N -e main -Ttext 0 -o _runproctest runproctest.o ulib.o usys.o printf.o umalloc.o console.o

make文件中可能还有其他ld命令有类似问题。

此外，根据错误消息，在用于创建 _runproctest 可执行文件的文件中的任何地方都没有 main() 函数。这(通常)强烈表明代码将无法正确执行。

顺便说一句:

以__ 或_ 后跟大写字母开头的名称是为环境保留的。

用前导下划线命名您自己的项目(可能)会起作用，但它会使环境 namespace 困惑。强烈建议不要在您的名字中使用任何前导 _