我的站点

一个系统软件工程师的随手涂鸦

Date: 十一月 30, 2015

SystemTap 笔记 (14)—— Tracing user-space程序需要安装debug-info包

SystemTap追踪user-space程序时需要安装user-space程序的debug-info包。举个例子:

 # stap -d /bin/ls --ldd -e 'probe process("ls").function("xmalloc") {print_usyms(ubacktrace())}' -c "ls /"
semantic error: while resolving probe point: identifier 'process' at <input>:1:7
        source: probe process("ls").function("xmalloc") {print_usyms(ubacktrace())}
                      ^

semantic error: no match (similar functions: malloc, calloc, realloc, close, mbrtowc)
Pass 2: analysis failed.  [man error::pass2]

安装coreutils-debuginfo包:

# zypper in coreutils-debuginfo
Loading repository data...
Reading installed packages...
Resolving package dependencies...

The following NEW package is going to be installed:
  coreutils-debuginfo

The following package is not supported by its vendor:
  coreutils-debuginfo

1 new package to install.
Overall download size: 2.1 MiB. Already cached: 0 B. After the operation, additional 18.6 MiB will be used.
Continue? [y/n/? shows all options] (y): y
Retrieving package coreutils-debuginfo-8.22-9.1.x86_64                                                (1/1),   2.1 MiB ( 18.6 MiB unpacked)
Retrieving: coreutils-debuginfo-8.22-9.1.x86_64.rpm ...................................................................[done (105.3 KiB/s)]
Checking for file conflicts: ........................................................................................................[done]
(1/1) Installing: coreutils-debuginfo-8.22-9.1 ......................................................................................[done]

再次执行上述命令:

# stap -d /bin/ls --ldd -e 'probe process("ls").function("xmalloc") {print_usyms(ubacktrace())}' -c "ls /"
bin  boot  dev  etc  home  lib  lib64  lost+found  mnt  opt  proc  root  run  sbin  selinux  srv  sys  tmp  usr  var
 0x4114a0 : xmalloc+0x0/0x20 [/usr/bin/ls]
 0x411674 : xmemdup+0x14/0x30 [/usr/bin/ls]
 0x40ee4a : clone_quoting_options+0x2a/0x40 [/usr/bin/ls]
 0x403828 : main+0xa58/0x2140 [/usr/bin/ls]
 0x7fad37eefb05 : __libc_start_main+0xf5/0x1c0 [/lib64/libc-2.19.so]
 0x404f39 : _start+0x29/0x30 [/usr/bin/ls]
 0x4114a0 : xmalloc+0x0/0x20 [/usr/bin/ls]
 0x411674 : xmemdup+0x14/0x30 [/usr/bin/ls]
 0x40ee4a : clone_quoting_options+0x2a/0x40 [/usr/bin/ls]
 0x403887 : main+0xab7/0x2140 [/usr/bin/ls]
 0x7fad37eefb05 : __libc_start_main+0xf5/0x1c0 [/lib64/libc-2.19.so]
 0x404f39 : _start+0x29/0x30 [/usr/bin/ls]
 0x4114a0 : xmalloc+0x0/0x20 [/usr/bin/ls]
 0x4039e4 : main+0xc14/0x2140 [/usr/bin/ls]
 0x7fad37eefb05 : __libc_start_main+0xf5/0x1c0 [/lib64/libc-2.19.so]
.....

 

Linux kernel 笔记 (58)——ioctl

ioctl系统调用的函数原型:

int ioctl(int fd, unsigned long cmd, ...);

In a real system, however, a system call can’t actually have a variable number of arguments. System calls must have a well-defined prototype, because user programs can access them only through hardware “gates.” Therefore, the dots in the prototype represent not a variable number of arguments but a single optional argument, traditionally identified as char *argp . The dots are simply there to prevent type checking during compilation. The actual nature of the third argument depends on the specific control command being issued (the second argument).

...并不是代表可变参数,而只是一个可选参数,...在这里防止编译时进行类型检查。

目前在struct file_operations结构体中已不再有ioctl成员:

int (*ioctl) (struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg);

取而代之是unlocked_ioctlcompat_ioctl

long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);

unlocked_ioctl代替ioctl,而compat_ioctl用在32位程序运行在64位操作系统上调用ioctl系统调用。

ioctl的命令是32-bit长,包含以下4个字段:

---------------------------------------------------------------
| dirction(2/3-bit)|size(14/13-bit)| type(8-bit)|number(8-bit)|

各个字段定义:

type
The magic number. Just choose one number (after consulting ioctl-number.txt) and use it throughout the driver. This field is eight bits wide ( IOCTYPEBITS ).

number
The ordinal (sequential) number. It’s eight bits ( IOCNRBITS ) wide.

direction
The direction of data transfer, if the particular command involves a data transfer. The possible values are IOCNONE (no data transfer), IOCREAD , IOCWRITE , and IOCREAD|IOCWRITE (data is transferred both ways). Data transfer is seen from the application’s point of view; IOCREAD means reading from the device, so the driver must write to user space. Note that the field is a bit mask, so IOC READ and IOCWRITE can be extracted using a logical AND operation.

size
The size of user data involved. The width of this field is architecture dependent, but is usually 13 or 14 bits. You can find its value for your specific architecture in the macro IOCSIZEBITS . It’s not mandatory that you use the size field—the kernel does not check it—but it is a good idea. Proper use of this field can help detect user-space programming errors and enable you to implement backward compatibility if you ever need to change the size of the relevant data item. If you need larger data structures, however, you can just ignore the size field. We’ll see how this field is used soon.

相关的macro定义:

extern unsigned int __invalid_size_argument_for_IOC;
#define _IOC_TYPECHECK(t) \
    ((sizeof(t) == sizeof(t[1]) && \
      sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
      sizeof(t) : __invalid_size_argument_for_IOC)

#define _IOC(dir,type,nr,size) \
    (((dir)  << _IOC_DIRSHIFT) | \
     ((type) << _IOC_TYPESHIFT) | \
     ((nr)   << _IOC_NRSHIFT) | \
     ((size) << _IOC_SIZESHIFT))

/* used to create numbers */
#define _IO(type,nr)        _IOC(_IOC_NONE,(type),(nr),0)
#define _IOR(type,nr,size)  _IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOW(type,nr,size)  _IOC(_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOWR(type,nr,size) _IOC(_IOC_READ|_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOR_BAD(type,nr,size)  _IOC(_IOC_READ,(type),(nr),sizeof(size))
#define _IOW_BAD(type,nr,size)  _IOC(_IOC_WRITE,(type),(nr),sizeof(size))
#define _IOWR_BAD(type,nr,size) _IOC(_IOC_READ|_IOC_WRITE,(type),(nr),sizeof(size))

/* used to decode ioctl numbers.. */
#define _IOC_DIR(nr)        (((nr) >> _IOC_DIRSHIFT) & _IOC_DIRMASK)
#define _IOC_TYPE(nr)       (((nr) >> _IOC_TYPESHIFT) & _IOC_TYPEMASK)
#define _IOC_NR(nr)     (((nr) >> _IOC_NRSHIFT) & _IOC_NRMASK)
#define _IOC_SIZE(nr)       (((nr) >> _IOC_SIZESHIFT) & _IOC_SIZEMASK)

参考资料:
The new way of ioctl()
Linux Kernel ioctl(), unlockedioctl(), and compatioctl()
Advanced Char Driver Operations

 

Haskell笔记 (3)—— list和tuple

(1)

Because strings are lists, we can use list functions on them.

举例如下:

> "Hello " ++ "world"
"Hello world"

(2)
:用来连接一个元素和list++连接两个list

>let list = [1, 2, 3, 4]
> print list
[1,2,3,4]
> [5] : list

<interactive>:23:1:
    Non type-variable argument in the constraint: Num [t]
    (Use FlexibleContexts to permit this)
    When checking that ‘it’ has the inferred type
      it :: forall t. (Num t, Num [t]) => [[t]]
> 5 : list
[5,1,2,3,4]

(3)

Ranges are a way of making lists that are arithmetic sequences of elements that can be enumerated. Numbers can be enumerated. One, two, three, four, etc. Characters can also be enumerated. The alphabet is an enumeration of characters from A to Z. Names can’t be enumerated. What comes after “John”?

举例如下:

> [1 .. 20]
[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

也可以指定元素之间的“步长”(24之间差2):

> [2, 4 .. 20]
[2,4,6,8,10,12,14,16,18,20]

另外,cycle循环一个list

cycle takes a list and cycles it into an infinite list. If you just try to display the result, it will go on forever so you have to slice it off somewhere.

> take 10 (cycle [1,2,3])  
[1,2,3,1,2,3,1,2,3,1]  
> take 12 (cycle "LOL ")  
"LOL LOL LOL "   

repeat循环一个元素

repeat takes an element and produces an infinite list of just that element. It’s like cycling a list with only one element.

> take 10 (repeat 5)  
[5,5,5,5,5,5,5,5,5,5]  

也可以使用replicate函数:

replicate function if you want some number of the same element in a list.

> replicate 10 5
[5,5,5,5,5,5,5,5,5,5]

(4)

list最后一个元素后面不能再跟,

>  [1,2]
[1,2]
> [1,2,]

<interactive>:12:6: parse error on input ‘]’

(5)

There’s a special type, () , that acts as a tuple of zero elements. This type has only one value, which is also written () . Both the type and the value are usually pronounced “unit.” If you are familiar with C, () is somewhat similar to void.

(6)fstsnd这两个函数只能操作包含两个元素的tuple

> :type fst
fst :: (a, b) -> a
> :type snd
snd :: (a, b) -> b

(7)

The list [1,2,3] in Haskell is actually shorthand for the list 1:(2:(3:[])), where [] is the empty list and : is the infix operator that adds its first argument to the front of its second argument (a list). (: and [] are like Lisp’s cons and nil, respectively.) Since : is right associative, we can also write this list as 1:2:3:[].

Linux kernel 笔记 (57)——hardware interrtupt不能访问userspace

以下摘自plka

Capture

系统调用(system call)可以访问userspace,而硬件中断(hardware interrupt)则不能。

Linux kernel 笔记 (56)——init进程

以下摘自plka

Linux employs a hierarchical scheme in which each process depends on a parent process. The kernel starts the init program as the first process that is responsible for further system initialization actions and display of the login prompt or (in more widespread use today) display of a graphical login interface. init is therefore the root from which all processes originate, more or less directly.

init进程是Linux运行的第一个进程,是其它所有进程的“祖先”

Powered by WordPress & Theme by Anders Norén