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| -rw-r--r-- | Documentation/s390/Debugging390.txt | 374 |
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diff --git a/Documentation/s390/Debugging390.txt b/Documentation/s390/Debugging390.txt index 2120eec48a5c..08911b5c6b0e 100644 --- a/Documentation/s390/Debugging390.txt +++ b/Documentation/s390/Debugging390.txt @@ -26,11 +26,6 @@ The Linux for s/390 & z/Architecture Kernel Task Structure Register Usage & Stackframes on Linux for s/390 & z/Architecture A sample program with comments Compiling programs for debugging on Linux for s/390 & z/Architecture -Figuring out gcc compile errors -Debugging Tools -objdump -strace -Performance Debugging Debugging under VM s/390 & z/Architecture IO Overview Debugging IO on s/390 & z/Architecture under VM @@ -740,376 +735,7 @@ Debugging with optimisation has since much improved after fixing some bugs, please make sure you are using gdb-5.0 or later developed after Nov'2000. -Figuring out gcc compile errors -=============================== -If you are getting a lot of syntax errors compiling a program & the problem -isn't blatantly obvious from the source. -It often helps to just preprocess the file, this is done with the -E -option in gcc. -What this does is that it runs through the very first phase of compilation -( compilation in gcc is done in several stages & gcc calls many programs to -achieve its end result ) with the -E option gcc just calls the gcc preprocessor (cpp). -The c preprocessor does the following, it joins all the files #included together -recursively ( #include files can #include other files ) & also the c file you wish to compile. -It puts a fully qualified path of the #included files in a comment & it -does macro expansion. -This is useful for debugging because -1) You can double check whether the files you expect to be included are the ones -that are being included ( e.g. double check that you aren't going to the i386 asm directory ). -2) Check that macro definitions aren't clashing with typedefs, -3) Check that definitions aren't being used before they are being included. -4) Helps put the line emitting the error under the microscope if it contains macros. - -For convenience the Linux kernel's makefile will do preprocessing automatically for you -by suffixing the file you want built with .i ( instead of .o ) - -e.g. -from the linux directory type -make arch/s390/kernel/signal.i -this will build - -s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer --fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce -E arch/s390/kernel/signal.c -> arch/s390/kernel/signal.i - -Now look at signal.i you should see something like. - - -# 1 "/home1/barrow/linux/include/asm/types.h" 1 -typedef unsigned short umode_t; -typedef __signed__ char __s8; -typedef unsigned char __u8; -typedef __signed__ short __s16; -typedef unsigned short __u16; - -If instead you are getting errors further down e.g. -unknown instruction:2515 "move.l" or better still unknown instruction:2515 -"Fixme not implemented yet, call Martin" you are probably are attempting to compile some code -meant for another architecture or code that is simply not implemented, with a fixme statement -stuck into the inline assembly code so that the author of the file now knows he has work to do. -To look at the assembly emitted by gcc just before it is about to call gas ( the gnu assembler ) -use the -S option. -Again for your convenience the Linux kernel's Makefile will hold your hand & -do all this donkey work for you also by building the file with the .s suffix. -e.g. -from the Linux directory type -make arch/s390/kernel/signal.s - -s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer --fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce -S arch/s390/kernel/signal.c --o arch/s390/kernel/signal.s - - -This will output something like, ( please note the constant pool & the useful comments -in the prologue to give you a hand at interpreting it ). - -.LC54: - .string "misaligned (__u16 *) in __xchg\n" -.LC57: - .string "misaligned (__u32 *) in __xchg\n" -.L$PG1: # Pool sys_sigsuspend -.LC192: - .long -262401 -.LC193: - .long -1 -.LC194: - .long schedule-.L$PG1 -.LC195: - .long do_signal-.L$PG1 - .align 4 -.globl sys_sigsuspend - .type sys_sigsuspend,@function -sys_sigsuspend: -# leaf function 0 -# automatics 16 -# outgoing args 0 -# need frame pointer 0 -# call alloca 0 -# has varargs 0 -# incoming args (stack) 0 -# function length 168 - STM 8,15,32(15) - LR 0,15 - AHI 15,-112 - BASR 13,0 -.L$CO1: AHI 13,.L$PG1-.L$CO1 - ST 0,0(15) - LR 8,2 - N 5,.LC192-.L$PG1(13) - -Adding -g to the above output makes the output even more useful -e.g. typing -make CC:="s390-gcc -g" kernel/sched.s - -which compiles. -s390-gcc -g -D__KERNEL__ -I/home/barrow/linux-2.3/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -fno-strict-aliasing -pipe -fno-strength-reduce -S kernel/sched.c -o kernel/sched.s - -also outputs stabs ( debugger ) info, from this info you can find out the -offsets & sizes of various elements in structures. -e.g. the stab for the structure -struct rlimit { - unsigned long rlim_cur; - unsigned long rlim_max; -}; -is -.stabs "rlimit:T(151,2)=s8rlim_cur:(0,5),0,32;rlim_max:(0,5),32,32;;",128,0,0,0 -from this stab you can see that -rlimit_cur starts at bit offset 0 & is 32 bits in size -rlimit_max starts at bit offset 32 & is 32 bits in size. - - -Debugging Tools: -================ - -objdump -======= -This is a tool with many options the most useful being ( if compiled with -g). -objdump --source <victim program or object file> > <victims debug listing > - - -The whole kernel can be compiled like this ( Doing this will make a 17MB kernel -& a 200 MB listing ) however you have to strip it before building the image -using the strip command to make it a more reasonable size to boot it. - -A source/assembly mixed dump of the kernel can be done with the line -objdump --source vmlinux > vmlinux.lst -Also, if the file isn't compiled -g, this will output as much debugging information -as it can (e.g. function names). This is very slow as it spends lots -of time searching for debugging info. The following self explanatory line should be used -instead if the code isn't compiled -g, as it is much faster: -objdump --disassemble-all --syms vmlinux > vmlinux.lst - -As hard drive space is valuable most of us use the following approach. -1) Look at the emitted psw on the console to find the crash address in the kernel. -2) Look at the file System.map ( in the linux directory ) produced when building -the kernel to find the closest address less than the current PSW to find the -offending function. -3) use grep or similar to search the source tree looking for the source file - with this function if you don't know where it is. -4) rebuild this object file with -g on, as an example suppose the file was -( /arch/s390/kernel/signal.o ) -5) Assuming the file with the erroneous function is signal.c Move to the base of the -Linux source tree. -6) rm /arch/s390/kernel/signal.o -7) make /arch/s390/kernel/signal.o -8) watch the gcc command line emitted -9) type it in again or alternatively cut & paste it on the console adding the -g option. -10) objdump --source arch/s390/kernel/signal.o > signal.lst -This will output the source & the assembly intermixed, as the snippet below shows -This will unfortunately output addresses which aren't the same -as the kernel ones you should be able to get around the mental arithmetic -by playing with the --adjust-vma parameter to objdump. - - - - -static inline void spin_lock(spinlock_t *lp) -{ - a0: 18 34 lr %r3,%r4 - a2: a7 3a 03 bc ahi %r3,956 - __asm__ __volatile(" lhi 1,-1\n" - a6: a7 18 ff ff lhi %r1,-1 - aa: 1f 00 slr %r0,%r0 - ac: ba 01 30 00 cs %r0,%r1,0(%r3) - b0: a7 44 ff fd jm aa <sys_sigsuspend+0x2e> - saveset = current->blocked; - b4: d2 07 f0 68 mvc 104(8,%r15),972(%r4) - b8: 43 cc - return (set->sig[0] & mask) != 0; -} - -6) If debugging under VM go down to that section in the document for more info. - - -I now have a tool which takes the pain out of --adjust-vma -& you are able to do something like -make /arch/s390/kernel/traps.lst -& it automatically generates the correctly relocated entries for -the text segment in traps.lst. -This tool is now standard in linux distro's in scripts/makelst - -strace: -------- -Q. What is it ? -A. It is a tool for intercepting calls to the kernel & logging them -to a file & on the screen. - -Q. What use is it ? -A. You can use it to find out what files a particular program opens. - - - -Example 1 ---------- -If you wanted to know does ping work but didn't have the source -strace ping -c 1 127.0.0.1 -& then look at the man pages for each of the syscalls below, -( In fact this is sometimes easier than looking at some spaghetti -source which conditionally compiles for several architectures ). -Not everything that it throws out needs to make sense immediately. - -Just looking quickly you can see that it is making up a RAW socket -for the ICMP protocol. -Doing an alarm(10) for a 10 second timeout -& doing a gettimeofday call before & after each read to see -how long the replies took, & writing some text to stdout so the user -has an idea what is going on. - -socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) = 3 -getuid() = 0 -setuid(0) = 0 -stat("/usr/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory) -stat("/usr/share/locale/libc/C", 0xbffff134) = -1 ENOENT (No such file or directory) -stat("/usr/local/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory) -getpid() = 353 -setsockopt(3, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0 -setsockopt(3, SOL_SOCKET, SO_RCVBUF, [49152], 4) = 0 -fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(3, 1), ...}) = 0 -mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40008000 -ioctl(1, TCGETS, {B9600 opost isig icanon echo ...}) = 0 -write(1, "PING 127.0.0.1 (127.0.0.1): 56 d"..., 42PING 127.0.0.1 (127.0.0.1): 56 data bytes -) = 42 -sigaction(SIGINT, {0x8049ba0, [], SA_RESTART}, {SIG_DFL}) = 0 -sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {SIG_DFL}) = 0 -gettimeofday({948904719, 138951}, NULL) = 0 -sendto(3, "\10\0D\201a\1\0\0\17#\2178\307\36"..., 64, 0, {sin_family=AF_INET, -sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 64 -sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0 -sigaction(SIGALRM, {0x8049ba0, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0 -alarm(10) = 0 -recvfrom(3, "E\0\0T\0005\0\0@\1|r\177\0\0\1\177"..., 192, 0, -{sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84 -gettimeofday({948904719, 160224}, NULL) = 0 -recvfrom(3, "E\0\0T\0006\0\0\377\1\275p\177\0"..., 192, 0, -{sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84 -gettimeofday({948904719, 166952}, NULL) = 0 -write(1, "64 bytes from 127.0.0.1: icmp_se"..., -5764 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=28.0 ms - -Example 2 ---------- -strace passwd 2>&1 | grep open -produces the following output -open("/etc/ld.so.cache", O_RDONLY) = 3 -open("/opt/kde/lib/libc.so.5", O_RDONLY) = -1 ENOENT (No such file or directory) -open("/lib/libc.so.5", O_RDONLY) = 3 -open("/dev", O_RDONLY) = 3 -open("/var/run/utmp", O_RDONLY) = 3 -open("/etc/passwd", O_RDONLY) = 3 -open("/etc/shadow", O_RDONLY) = 3 -open("/etc/login.defs", O_RDONLY) = 4 -open("/dev/tty", O_RDONLY) = 4 - -The 2>&1 is done to redirect stderr to stdout & grep is then filtering this input -through the pipe for each line containing the string open. - - -Example 3 ---------- -Getting sophisticated -telnetd crashes & I don't know why - -Steps ------ -1) Replace the following line in /etc/inetd.conf -telnet stream tcp nowait root /usr/sbin/in.telnetd -h -with -telnet stream tcp nowait root /blah - -2) Create the file /blah with the following contents to start tracing telnetd -#!/bin/bash -/usr/bin/strace -o/t1 -f /usr/sbin/in.telnetd -h -3) chmod 700 /blah to make it executable only to root -4) -killall -HUP inetd -or ps aux | grep inetd -get inetd's process id -& kill -HUP inetd to restart it. - -Important options ------------------ --o is used to tell strace to output to a file in our case t1 in the root directory --f is to follow children i.e. -e.g in our case above telnetd will start the login process & subsequently a shell like bash. -You will be able to tell which is which from the process ID's listed on the left hand side -of the strace output. --p<pid> will tell strace to attach to a running process, yup this can be done provided - it isn't being traced or debugged already & you have enough privileges, -the reason 2 processes cannot trace or debug the same program is that strace -becomes the parent process of the one being debugged & processes ( unlike people ) -can have only one parent. - - -However the file /t1 will get big quite quickly -to test it telnet 127.0.0.1 - -now look at what files in.telnetd execve'd -413 execve("/usr/sbin/in.telnetd", ["/usr/sbin/in.telnetd", "-h"], [/* 17 vars */]) = 0 -414 execve("/bin/login", ["/bin/login", "-h", "localhost", "-p"], [/* 2 vars */]) = 0 -Whey it worked!. - - -Other hints: ------------- -If the program is not very interactive ( i.e. not much keyboard input ) -& is crashing in one architecture but not in another you can do -an strace of both programs under as identical a scenario as you can -on both architectures outputting to a file then. -do a diff of the two traces using the diff program -i.e. -diff output1 output2 -& maybe you'll be able to see where the call paths differed, this -is possibly near the cause of the crash. - -More info ---------- -Look at man pages for strace & the various syscalls -e.g. man strace, man alarm, man socket. - - -Performance Debugging -===================== -gcc is capable of compiling in profiling code just add the -p option -to the CFLAGS, this obviously affects program size & performance. -This can be used by the gprof gnu profiling tool or the -gcov the gnu code coverage tool ( code coverage is a means of testing -code quality by checking if all the code in an executable in exercised by -a tester ). - - -Using top to find out where processes are sleeping in the kernel ----------------------------------------------------------------- -To do this copy the System.map from the root directory where -the linux kernel was built to the /boot directory on your -linux machine. -Start top -Now type fU<return> -You should see a new field called WCHAN which -tells you where each process is sleeping here is a typical output. - - 6:59pm up 41 min, 1 user, load average: 0.00, 0.00, 0.00 -28 processes: 27 sleeping, 1 running, 0 zombie, 0 stopped -CPU states: 0.0% user, 0.1% system, 0.0% nice, 99.8% idle -Mem: 254900K av, 45976K used, 208924K free, 0K shrd, 28636K buff -Swap: 0K av, 0K used, 0K free 8620K cached - - PID USER PRI NI SIZE RSS SHARE WCHAN STAT LIB %CPU %MEM TIME COMMAND - 750 root 12 0 848 848 700 do_select S 0 0.1 0.3 0:00 in.telnetd - 767 root 16 0 1140 1140 964 R 0 0.1 0.4 0:00 top - 1 root 8 0 212 212 180 do_select S 0 0.0 0.0 0:00 init - 2 root 9 0 0 0 0 down_inte SW 0 0.0 0.0 0:00 kmcheck - -The time command ----------------- -Another related command is the time command which gives you an indication -of where a process is spending the majority of its time. -e.g. -time ping -c 5 nc -outputs -real 0m4.054s -user 0m0.010s -sys 0m0.010s Debugging under VM ================== |