另一种学习 Linux kernel 的方式 —— UML

make defconfig ARCH=um SUBARCH=x86_64make linux ARCH=um SUBARCH=x86_64 -j `nproc`

❯ ./linux --helpUser Mode Linux v6.1.65    available at http://user-mode-linux.sourceforge.net/
--showconfig    Prints the config file that this UML binary was generated from.
......
hostfs=<root dir>,<flags>,...    This is used to set hostfs parameters.  The root directory argument    is used to confine all hostfs mounts to within the specified directory    tree on the host.  If this isn't specified, then a user inside UML can    mount anything on the host that's accessible to the user that's running    it.    The only flag currently supported is 'append', which specifies that all    files opened by hostfs will be opened in append mode.

mkdir -p rootfscurl https://dl-cdn.alpinelinux.org/alpine/v3.18/main/x86_64/apk-tools-static-2.14.0-r2.apk | fakeroot tar -xz -C rootfs

fakeroot rootfs/sbin/apk.static \    --repository https://dl-cdn.alpinelinux.org/alpine/v3.18/main --update-cache \    --allow-untrusted \    --root $PWD/rootfs --initdb add alpine-baseecho https://dl-cdn.alpinelinux.org/alpine/v3.18/main > rootfs/etc/apk/repositoriesecho "LABEL=ALPINE_ROOT / auto defaults 1 1" >> rootfs/etc/fstab

#!/bin/sh./linux ubd0=/dev/null umid=uml0 \        root=/dev/root rootfstype=hostfs hostfs=./rootfs \        rw mem=64M init=/bin/sh quietstty sane ; echo

~ # /bin/busybox --install~ # mount -t proc none /proc

~ # cat /proc/cpuinfo processor  : 0vendor_id  : User Mode Linuxmodel name  : UMLmode    : skashost    : Linux yuan-T14p 6.2.0-37-generic #38~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov  2 18:01:13 UTC 2 x86_64fpu    : yesflags    : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 pn clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall mp nx pdpe1gb rdtscp lm 3dnow constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cid sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb pti ssbd ibrs ibpb stibp ibrs_enhanced tpr_shadow vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid rdseed adx smap clflushopt clwb intel_pt sha_ni xsaveopt xsavec xgetbv1 xsaves avx_vnni brs dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp hwp_pkg_req hfi umip pku ospke waitpkg gfni vaes vpclmulqdq tme rdpid movdiri movdir64b fsrm md_clear serialize pconfig arch_lbr ibt flush_l1d arch_capabilities smecache_alignment  : 64bogomips  : 10738.07

wget -O rootfs/sbin/tini https://github.com/krallin/tini/releases/download/v0.19.0/tini-staticchmod +x rootfs/sbin/tini

#!/bin/sh
mount -t proc proc /procmount -t sysfs sys /sys
ip link set eth0 upip address add 192.168.100.101/24 dev eth0
export PS1='\[\033[01;32mUML:\w\033[00m \$ 'exec /sbin/tini /bin/sh +m

#!/bin/sh./linux ubd0=/dev/null umid=uml0 hostname=uml1 eth0=tuntap,tap0 \        root=/dev/root rootfstype=hostfs hostfs=./rootfs \        rw mem=64M init=/init.sh quietstty sane ; echo

/* linux/fs.h */- LX_VALUE(SB_RDONLY)- LX_VALUE(SB_SYNCHRONOUS)- LX_VALUE(SB_MANDLOCK)- LX_VALUE(SB_DIRSYNC)- LX_VALUE(SB_NOATIME)- LX_VALUE(SB_NODIRATIME)+ LX_GDBPARSED(SB_RDONLY)+ LX_GDBPARSED(SB_SYNCHRONOUS)+ LX_GDBPARSED(SB_MANDLOCK)+ LX_GDBPARSED(SB_DIRSYNC)+ LX_GDBPARSED(SB_NOATIME)+ LX_GDBPARSED(SB_NODIRATIME)

echo "CONFIG_GDB_SCRIPTS=y" > .config-fragmentARCH=um scripts/kconfig/merge_config.sh .config .config-fragmentmake ARCH=um scripts_gdb

❯ gdb -ex "add-auto-load-safe-path scripts/gdb/vmlinux-gdb.py" \      -ex "file vmlinux" \      -ex "lx-version" -qReading symbols from vmlinux...Linux version 6.1.65 (yuan@yuan-T14p) (gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, GNU ld (GNU Binutils for Ubuntu) 2.38) #1 Wed Dec  6 21:00:15 CST 2023(gdb) 

python gdb.COMPLETE_EXPRESSION = gdb.COMPLETE_SYMBOLadd-auto-load-safe-path scripts/gdb/vmlinux-gdb.pyfile vmlinuxlx-versionset args ubd0=/dev/null umid=uml0 hostname=uml1 eth0=tuntap,tap0 root=/dev/root rootfstype=hostfs rootflags=${FULLPATH}/rootfs rw mem=64M init=/init.sh quiethandle SIGSEGV nostop noprinthandle SIGUSR1 nopass stop print

gdb -q -x gdbinit(gdb) run

UML:~ #         Thread 1 "vmlinux" received signal SIGUSR1, User defined signal 1.                                                                          0x00007ffff7c427dc in __GI___sigsuspend (set=set@entry=0x604c7db0) at ../sysdeps/unix/sysv/linux/sigsuspend.c:2626  ../sysdeps/unix/sysv/linux/sigsuspend.c: No such file or directory.(gdb) b cmdline_proc_showBreakpoint 1 at 0x6014c793: file fs/proc/cmdline.c, line 8.(gdb) cContinuing.
UML:~ # cat /proc/cmdline
Thread 1 "vmlinux" hit Breakpoint 1, cmdline_proc_show (m=0x60a6a690, v=0x1) at fs/proc/cmdline.c:88  {(gdb) bt#0  cmdline_proc_show (m=0x60a6a690, v=0x1) at fs/proc/cmdline.c:8#1  0x000000006010f41e in seq_read_iter (iocb=0x6489fc40, iter=0x6489fc18) at fs/seq_file.c:230#2  0x0000000060144a37 in proc_reg_read_iter (iocb=<optimized out>, iter=<optimized out>) at fs/proc/inode.c:305#3  0x00000000601163af in call_read_iter (file=0x60808100, file=0x60808100, iter=0x6489fc18, kio=0x6489fc40)    at ./include/linux/fs.h:2242#4  generic_file_splice_read (in=0x60808100, ppos=0x6489fd28, pipe=0x60a5a240, len=<optimized out>, flags=<optimized out>)    at fs/splice.c:309#5  0x000000006011623d in do_splice_to (in=in@entry=0x60808100, ppos=ppos@entry=0x6489fd28, pipe=pipe@entry=0x60a5a240, len=65536,     len@entry=16777216, flags=flags@entry=0) at fs/splice.c:793#6  0x0000000060116d5b in splice_direct_to_actor (in=in@entry=0x60808100, sd=sd@entry=0x6489fd78,     actor=actor@entry=0x60115ece <direct_splice_actor>) at fs/splice.c:865#7  0x0000000060116eb8 in do_splice_direct (in=in@entry=0x60808100, ppos=ppos@entry=0x6489fdf8, out=out@entry=0x60808b00,     opos=opos@entry=0x6489fe00, len=len@entry=16777216, flags=flags@entry=0) at fs/splice.c:974#8  0x00000000600e9a4e in do_sendfile (out_fd=<optimized out>, in_fd=<optimized out>, ppos=ppos@entry=0x0, count=16777216,     max=2147483647, max@entry=0) at fs/read_write.c:1255#9  0x00000000600ea90f in __do_sys_sendfile64 (count=<optimized out>, offset=<optimized out>, in_fd=<optimized out>,     out_fd=<optimized out>) at fs/read_write.c:1323#10 __se_sys_sendfile64 (out_fd=<optimized out>, in_fd=<optimized out>, offset=<optimized out>, count=<optimized out>)    at fs/read_write.c:1309#11 0x00000000600231ee in handle_syscall (r=r@entry=0x60a5ebc0) at arch/um/kernel/skas/syscall.c:45#12 0x0000000060035cc3 in handle_trap (local_using_sysemu=2, regs=0x60a5ebc0, pid=75674) at arch/um/os-Linux/skas/process.c:224#13 userspace (regs=0x60a5ebc0, aux_fp_regs=0x6489c020) at arch/um/os-Linux/skas/process.c:480#14 0x000000006001ff37 in fork_handler () at arch/um/kernel/process.c:154#15 0x0000000000000000 in ?? ()Backtrace stopped: Cannot access memory at address 0x648a0000(gdb)