昨天完成了lab4，今天开启了lab5。
Lab 5: File system, Spawn, and Shella
按照getting stared的流程走，当执行完git merge lab4后，想执行一下make指令看看是否这段ok，结果报错，如下所示：
lib/spawn.c:110:42: error: taking address of packed member of ‘struct Trapframe’ may result in an unaligned pointer value [-Werror=address-of-packed-member]
110 | if ((r = init_stack(child, argv, &child_tf.tf_esp)) < 0)
| ^~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make: *** [lib/Makefrag:37: obj/lib/spawn.o] Error 1
我们可以注意到这行：
cc1: all warnings being treated as errors
报错原因就如该行英文的字面意思，因此想到去修改GNUmakefile中的Werror
打开lab5/下的GNUmakefile
#
# This makefile system follows the structuring conventions
# recommended by Peter Miller in his excellent paper:
#
# Recursive Make Considered Harmful
# http://aegis.sourceforge.net/auug97.pdf
#
OBJDIR := obj
# Run 'make V=1' to turn on verbose commands, or 'make V=0' to turn them off.
ifeq ($(V),1)
override V =
endif
ifeq ($(V),0)
override V = @
endif
-include conf/lab.mk
-include conf/env.mk
LABSETUP ?= ./
TOP = .
命令模式下输入
/Werror可以在92行这里发现它：
84 # Compiler flags
85 # -fno-builtin is required to avoid refs to undefined functions in the kernel.
86 # Only optimize to -O1 to discourage inlining, which complicates backtraces.
87 CFLAGS := $(CFLAGS) $(DEFS) $(LABDEFS) -O1 -fno-builtin -I$(TOP) -MD
88 CFLAGS += -fno-omit-frame-pointer
89 CFLAGS += -std=gnu99
90 CFLAGS += -static
91 CFLAGS += -fno-pie
92 CFLAGS += -Wall -Wno-format -Wno-unused -Werror -gstabs -m32
93 # -fno-tree-ch prevented gcc from sometimes reordering read_ebp() before
94 # mon_backtrace()'s function prologue on gcc version: (Debian 4.7.2-5) 4.7.2
95 CFLAGS += -fno-tree-ch
96
97 # Add -fno-stack-protector if the option exists.
98 CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-pr otector)
92 CFLAGS += -Wall -Wno-format -Wno-unused -Werror -gstabs -m32将-Werror删除，即变成以下内容：
92 CFLAGS += -Wall -Wno-format -Wno-unused -gstabs -m32
保存后重新make，可见该处变成了warning
+ cc[USER] lib/spawn.c
lib/spawn.c: In function ‘spawn’:
lib/spawn.c:110:42: warning: taking address of packed member of ‘struct Trapframe’ may result in an unal igned pointer value [-Waddress-of-packed-member]
110 | if ((r = init_stack(child, argv, &child_tf.tf_esp)) < 0)
| ^~~~~~~~~~~~~~~~
+ cc[USER] lib/pipe.c
当以为可以正常做实验的时候，发现竟然后续又来了一个报错：
+ cc[USER] fs/ide.c
+ cc[USER] fs/bc.c
+ cc[USER] fs/fs.c
+ cc[USER] fs/serv.c
+ cc[USER] fs/test.c
+ ld obj/fs/fs
ld: obj/fs/bc.o: in function `bc_pgfault':
fs/bc.c:31: multiple definition of `super'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/bc.o: in function `bc_pgfault':
fs/bc.c:31: multiple definition of `bitmap'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/fs.o: in function `walk_path':
fs/fs.c:233: multiple definition of `super'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/fs.o: in function `walk_path':
fs/fs.c:233: multiple definition of `bitmap'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/serv.o: in function `serve_read':
fs/serv.c:218: multiple definition of `bitmap'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/serv.o: in function `serve_read':
fs/serv.c:218: multiple definition of `super'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/test.o: in function `fs_test':
fs/test.c:10: multiple definition of `bitmap'; obj/fs/ide.o:fs/ide.c:19: first defined here
ld: obj/fs/test.o: in function `fs_test':
fs/test.c:10: multiple definition of `super'; obj/fs/ide.o:fs/ide.c:19: first defined here
make: *** [fs/Makefrag:52: obj/fs/fs] Error 1
仔细一看，直接人傻了，fs不是在lab5才刚刚新增的吗？怎么上来就报multiple definition错误？？？？？？？？？
发现CSDN上似乎没有相关内容的解决方式。经过一段时间的研究后，发现应该这样修改：
打开fs/fs.c，如下所示
1 #include <inc/string.h>
2 #include <inc/partition.h>
3
4 #include "fs.h"
5
6 // --------------------------------------------------------------
7 // Super block
8 // --------------------------------------------------------------
9
10 // Validate the file system super-block.
11 void
12 check_super(void)
13 {
14 if (super->s_magic != FS_MAGIC)
15 panic("bad file system magic number");
16
17 if (super->s_nblocks > DISKSIZE/BLKSIZE)
18 panic("file system is too large");
19
20 cprintf("superblock is good\n");
21 }
在其中加上两行（下图的第6行和第7行）：
1 #include <inc/string.h>
2 #include <inc/partition.h>
3
4 #include "fs.h"
5
6 struct Super *super;
7 uint32_t *bitmap;
8
9 // --------------------------------------------------------------
10 // Super block
11 // --------------------------------------------------------------
12
13 // Validate the file system super-block.
再打开fs/fs.h，如下所示
1 #include <inc/fs.h>
2 #include <inc/lib.h>
3
4 #define SECTSIZE 512 // bytes per disk sector
5 #define BLKSECTS (BLKSIZE / SECTSIZE) // sectors per block
6
7 /* Disk block n, when in memory, is mapped into the file system
8 * server's address space at DISKMAP + (n*BLKSIZE). */
9 #define DISKMAP 0x10000000
10
11 /* Maximum disk size we can handle (3GB) */
12 #define DISKSIZE 0xC0000000
13
14 struct Super *super; // superblock
15 uint32_t *bitmap; // bitmap blocks mapped in memory
16
17 /* ide.c */
18 bool ide_probe_disk1(void);
19 void ide_set_disk(int diskno);
20 void ide_set_partition(uint32_t first_sect, uint32_t nsect);
21 int ide_read(uint32_t secno, void *dst, size_t nsecs);
22 int ide_write(uint32_t secno, const void *src, size_t nsecs);
将其中的14，15行前加上extern
11 /* Maximum disk size we can handle (3GB) */
12 #define DISKSIZE 0xC0000000
13
14 extern struct Super *super; // superblock
15 extern uint32_t *bitmap; // bitmap blocks mapped in memory
16
保存后返回，然后运行make，即可成功！
参考文献：Mark global variables as extern · fisop/jos@1cb1e47 · GitHub