技术 – Page 16

gdb调试有管道的命令行

July 21, 2021June 30, 2021 by euhat

以pcre2调试为例

#!/bin/sh
 
cd `pwd`/installed/bin
 
mkfifo /tmp/pcre
echo "<h1>hello</h1>" > /tmp/pcre &
 
gdb ./pcre2grep -ex 'b main' -ex 'r -o "<.*>" < /tmp/pcre'
rm /tmp/pcre

refer to:
http://www.voidcn.com/article/p-migwptlv-bsq.html

apt testing source

July 1, 2021June 25, 2021 by euhat

/etc/apt/sources.list

deb http://http.us.debian.org/debian/ testing non-free contrib main
#deb http://http.us.debian.org/debian/ stable non-free contrib main
#deb http://http.us.debian.org/debian/ unstable non-free contrib main
#deb http://http.us.debian.org/debian/ wheezy non-free contrib main

1 2	#apt edit-sources apt update

NO_PUBKEY 04EE7237B7D453EC NO_PUBKEY 648ACFD622F3D138

1 2	apt-key adv --keyserver keyserver.ubuntu.com --recv 04EE7237B7D453EC apt-key adv --keyserver keyserver.ubuntu.com --recv 648ACFD622F3D138

ubuntu repo names

1
2
3

wheezy: debian 7.0
xenial: Ubuntu 16.04
focal: Ubuntu 20.04

refer to:
https://serverfault.com/questions/550855/how-to-add-debian-testing-repository-to-apt-get
https://yunwei365.blog.csdn.net/article/details/114930145

in gdb tui mode scroll the command window

February 2, 2022June 24, 2021 by euhat

Use cgdb instead.

Let GDBW denote the command window,
let SRCW denote the source window
let TTYW denote the input window.

Cgdb basic usage

ESC key in GDBW: switch to SRCW
i key in SRCW: switch to GDBW
T key in SRCW: switch on/off TTYW
PgUp/PgDn key in GDBW: scroll GDBW
PgUp/PgDn key in SRCW: scroll SRCW
-/= in SRCW: decrease/increase SRCW size

Patch: GDBW output is truncated.
cgdb/scroller.cpp:146
https://github.com/cgdb/cgdb/pull/269

refer to:
https://github.com/cgdb/cgdb/blob/master/doc/cgdb.texi

webrtc备忘录

March 11, 2022June 17, 2021 by euhat

名词

I帧: Intra-coded picture
P帧: Predictive-coded Picture
B帧: Bidirectionally predicted picture
GOP: Group of Pictures
IDR: Instantaneous Decoding Refresh
DTS: Decoding Time Stamp
PTS: Presentation Time Stamp

WebRTC 之视频捕获
https://hyjk2000.github.io/2015/04/21/webrtc-video-capture/
https://github.com/uxctx/DesktopLiveStreaming

so动态库只导出指定函数

June 10, 2021 by euhat

retain_sym.txt

1 2	func1 func2

ver_script.txt

LIBA_1.1 {
	global:
		foo1;
		foo2;
	local:
		*;
};

1	ld -shared --retain-symbols-file=retain_sym.txt --version-script=ver_script.txt tst.o -o tst.so

refer to:
https://blog.csdn.net/chdhust/article/details/79356717
http://blog.sina.com.cn/s/blog_493667730100csde.html
http://www.gnu.org/software/gnulib/manual/html_node/LD-Version-Scripts.html

linux命令备忘录

February 27, 2023June 4, 2021 by euhat

名词

pie: position-independent executable
pic: position-independent code
aslr: address space layout randomization
got: global offset table
vdso: virtual dynamic shared object

Basic command

grep [OPTION]... PATTERNS [FILE]...
find [-H] [-L] [-P] [-Olevel] [-D debugopts] [path...] [expression]
find . -size +2G -exec du -sh {} \;
ps axl | grep VirtualBoxVM | grep -v grep | awk '{print $3};'
cat /etc/passwd | sort -k5,5 -t: | column -t -s:
while true; do echo sleep 1 sec; sleep 1; cat /home/work/aa.txt 2>/dev/null && echo ok && break; done
echo first | xargs -i echo {} second
 
cat /etc/shadow
sudo !!
 
cd other_dir
cd - # return back

swap文件

dd if=/dev/zero of=./swap_file bs=1G count=8
mkswap ./swap_file
swapon ./swap_file
swapoff ./swap_file

objcopy

1
2
3

objcopy -I binary -O elf32-i386 -B i386 test.jpg test.o
objdump -s -b binary test.o
readelf -s test.o

静态链编stdc++

1	-Bstatic -lstdc++ -Bdynamic

工具

systemtap
inotify-tools
windres
reptyr
nmcli
nmtui

自启动

#/lib/systemd/system/mytask.service
#ln -s /lib/systemd/system/mytask.service /etc/systemd/system/multi-user.target.wants/mytask.service
[Unit]
Description=mytask
After=network.target
 
[Service]
Type=simple
ExecStart=mytask.sh
 
[Install]
WantedBy=multi-user.target

ubuntu

#网络配置文件路径，默认DHCP的连接不会生成文件
/etc/NetworkManager/system-connections/
#run arm64 binary on x86
dpkg --add-architecture armhf && apt-get update && apt-get install libc6:armhf
cat /proc/sys/fs/binfmt_misc/
qemu-user -L /home/bamanzi/i386-libs ./prog
#disable background process
systemctl disable unattended-upgrades
ss -tap
pv -d <pid>

centos

#网络配置文件路径
/etc/sysconfig/network-scripts/ifcfg-
#compiz
https://spins.fedoraproject.org/mate-compiz/download/index.html

refer to:
http://blog.chinaunix.net/uid-28461677-id-5766451.html
https://blog.csdn.net/weixin_33842304/article/details/91443399
https://unix.stackexchange.com/questions/4034/how-can-i-disown-a-running-process-and-associate-it-to-a-new-screen-shell
https://blog.csdn.net/wuzhong8809/article/details/117450302
https://stackoverflow.com/questions/18312935/find-file-in-linux-then-report-the-size-of-file-searched
https://www.toutiao.com/a7073448755428688399/
https://www.likecs.com/show-695436.html

Optimizing the kernel for VMware

March 23, 2022June 1, 2021 by euhat

[*] 64-bit kernel (leave blank for x86)
 
General Setup --->
  [*] Optimize very unlikely/likely branches
 
Power management and ACPI options --->
  [*] ACPI (Advanced Configuration and Power Interface) Support --->
 
Processor type and features --->
  Processor Family (usually Core2/Newer Xeon)
 
Bus Options --->
  < > PCCard (PCMCIA/Cardbus) support
 
Networking support --->
  [ ] Amateur Radio support
  [ ] Wireless (only if you plan on using nat EXCLUSIVELY)
 
Device Drivers --->
  Generic Driver Options
    [*] Maintain a devtmpfs filesystem to mount at /dev
 
  Misc Devices --->
    [*] VMware Balloon Driver (manages memory between VM and host)
    [*] VMware VMCI Driver (Virtual Machine Communication Interface - low-latency access to host memory bus)
 
  SCSI device support --->
    [*] SCSI low-level drivers --->
      <*> VMware PVSCSI driver support (high throughput storage adapter)
 
  [*] Fusion MPT device support --->
    <*> Fusion MPT ScsiHost drivers for SPI
 
  [*] Network device support --->
    [*] Ethernet driver support --->
      (disable every driver but this)
      [*] AMD Devices
        <*> AMD PCNet32 PCI support
    [ ] Wireless LAN (ONLY if you disabled Wireless networking support above)
    < > VMware VMXNET3 ethernet driver (PCNet32 is more than enough for most use cases - enable this only if you have spare cpu cycles to burn)
 
  Graphics support --->
    <*> Direct Rendering Manager
    < > Intel 8xx/9xx/G3x/G4x/HD Graphics
    <*> DRM driver for VMware Virtual GPU
      [*] Enable framebuffer console support under vmwgfx by default
    <*> Support for frame buffer devices
 
    Console display driver support --->
      <*> Framebuffer Console support
 
  Sound card support --->
    <*> Advanced Linux Sound Architecture --->
      [*] PCI sound devices
        <*> (Creative) Ensoniq AudioPCI 1371/1373
        < > Intel HD Audio
 
  File systems --->
    (enable only those you anticipate using)
    <*> Second extended fs support
    <*> The Extended 4 (ext4) filesystem
    <*> XFS filesystem support
    <*> Btrfs filesystem Unstable disk format
 
    Pseudo filesystems --->
      [*] Tmpfs virtual memory file system support (former shm fs)
        [*] Tmpfs POSIX Access Control Lists

[*] 64-bit kernel (leave blank for x86) General Setup ---> [*] Optimize very unlikely/likely branches Power management and ACPI options ---> [*] ACPI (Advanced Configuration and Power Interface) Support ---> Processor type and features ---> Processor Family (usually Core2/Newer Xeon) Bus Options ---> < > PCCard (PCMCIA/Cardbus) support Networking support ---> [ ] Amateur Radio support [ ] Wireless (only if you plan on using nat EXCLUSIVELY) Device Drivers ---> Generic Driver Options [*] Maintain a devtmpfs filesystem to mount at /dev Misc Devices ---> [*] VMware Balloon Driver (manages memory between VM and host) [*] VMware VMCI Driver (Virtual Machine Communication Interface - low-latency access to host memory bus) SCSI device support ---> [*] SCSI low-level drivers ---> <*> VMware PVSCSI driver support (high throughput storage adapter) [*] Fusion MPT device support ---> <*> Fusion MPT ScsiHost drivers for SPI [*] Network device support ---> [*] Ethernet driver support ---> (disable every driver but this) [*] AMD Devices <*> AMD PCNet32 PCI support [ ] Wireless LAN (ONLY if you disabled Wireless networking support above) < > VMware VMXNET3 ethernet driver (PCNet32 is more than enough for most use cases - enable this only if you have spare cpu cycles to burn) Graphics support ---> <*> Direct Rendering Manager < > Intel 8xx/9xx/G3x/G4x/HD Graphics <*> DRM driver for VMware Virtual GPU [*] Enable framebuffer console support under vmwgfx by default <*> Support for frame buffer devices Console display driver support ---> <*> Framebuffer Console support Sound card support ---> <*> Advanced Linux Sound Architecture ---> [*] PCI sound devices <*> (Creative) Ensoniq AudioPCI 1371/1373 < > Intel HD Audio File systems ---> (enable only those you anticipate using) <*> Second extended fs support <*> The Extended 4 (ext4) filesystem <*> XFS filesystem support <*> Btrfs filesystem Unstable disk format Pseudo filesystems ---> [*] Tmpfs virtual memory file system support (former shm fs) [*] Tmpfs POSIX Access Control Lists

efi boot (uncertain, maybe need to ask pc maker for signing the kernel.)

Processor type and features --->
  [*] EFI runtime service support 
  [*]   EFI stub support
Firmware Drivers  --->
   EFI (Extensible Firmware Interface) Support  --->
       <*> EFI Variable Support via sysfs

device mapper

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2
3

Device Drivers
	Multiple devices driver support (RAID and LVM)
		<M>   Device mapper support

refer to:
https://forums.gentoo.org/viewtopic-p-7332884.html
https://stackoverflow.com/questions/40344484/cant-load-self-compiled-linux-kernel

kprobe and uprobe

June 1, 2021 by euhat

kprobe

cd /sys/kernel/debug/tracing
echo 'p:myprobe do_sys_open' > kprobe_events
echo 'r:myretprobe do_sys_open $retval' > kprobe_events
echo 'r:myprobe getname +0($retval):string' > kprobe_events
echo 1 > tracing_on
echo 1 > events/kprobes/myprobe/enable
echo '-:myprobe' > kprobe_events
cat trace

uprobe

cd /sys/kernel/debug/tracing
echo 'p:do_sth /home/kernel_test/loop_print:0x52d %ip %ax' > uprobe_events
echo 'r:do_sth_exit /home/kernel_test/loop_print:0x52d %ip %ax' >> uprobe_events
echo 1 > events/uprobes/enable
cat trace

refer to:
https://blog.csdn.net/melody157398/article/details/113764679
https://blog.csdn.net/daiq531/article/details/52749673

asn.1中的方括号

October 10, 2021May 20, 2021 by euhat

asn.1编码以tag + length + value为基本单元，IMPLICIT模式是用context-specific tag替换后面通常是universal的tag；EXPLICIT模式是用context-specific tag的tlv包裏里层的universal tag的tlv。

ber编码时，会默认为EXPLICIT模式。

在bnf范式语法中

圆括号(): 相当于C语言算术表达式中圆括号()的作用。
尖括号<>: 内包含的为必选项。 
方括号[]: 内包含的为可选项。 
花括号{}: 内包含的为可重复0至无数次的项。 
|: 或or的意思；若要表示并and的意思，直接两个符号之间空白间隔。

而在asn.1语法中，方括号[Index]指示的是context-specific tag值，即0xA0 + Index；花括号{}用于SEQUENCE，SET或CHOICE的定义。如

1 2	Number2 ::= [7] IMPLICIT [1] INTEGER AccountedClosed ::= [2] EXPLICIT BOOLEAN

这里Number2的tag值为0xA7；而对于AccountedClosed，当其值为true时其ber编码为

1	0xA2 0x3 0x1 0x1 0xFF

refer to:
https://blog.csdn.net/sever2012/article/details/7767867
https://www.cnblogs.com/qook/p/5957436.html

数字证书备忘录

October 21, 2021May 20, 2021 by euhat

ca: certification authority
pem: privacy enhanced mail, "begin"+base64+"end"
der: distinguished encoding rules, binary
crt: certificate
cer: certificate
csr: certificate signing request
pkcs: public key cryptography standard
ietf: internet engineering task force
pkcs#12/pfx/p12: file format encoding private keys, certificates and etc, rfc7292
pkcs#7: cryptographic message syntex standard
pkcs#10/p10: certification request syntax specification, rfc2986
x.509: public key certificates format standard
ber: basic encoding rules
per: packed encoding rules
crl: certificate revocation list
dsa: digital signature algorithm

refer to:
http://www.360doc.com/content/15/0520/10/21412_471902987.shtml
https://baike.baidu.com/item/BER/19940289?fr=aladdin
https://blog.csdn.net/mao834099514/article/details/109074661
https://datatracker.ietf.org/doc/html/rfc7292