Moved archived notes from html to md. 5 Articles

5 files changed, 600 insertions, 0 deletions

diff --git a/md/writeup/asciitex_ascii_text_formating_utility.md b/md/writeup/asciitex_ascii_text_formating_utility.md
new file mode 100644
index 0000000..5b89eac
--- /dev/null
+++ b/md/writeup/asciitex_ascii_text_formating_utility.md
@@ -0,0 +1,25 @@
+title:ASCIITex ascii text formatting utility
+keywords:ascii,utilities
+
+# ASCIITex ascii text formatting utility
+
+ASCIITex is attempt to write tool that formats text to ascii style.
+Format width to 80 char width add some title generation and support of RFC
+is planned in future. With this tool should be possible to generate
+e-zines ;].
+
+Use:
+Minimal features and its usable for real world ascii text.
+
+```bash
+./asciitex file.at file.txt
+```
+
+
+## Links
+https://github.com/FreeArtMan/asciitex
+
+## Downloads
+http://archive.main.lv/files/writeup/asciitex_ascii_text_formating_utility/asciitex-0.0.2.tar.gz
+
+
diff --git a/md/writeup/create_elf_file_from_scratch.md b/md/writeup/create_elf_file_from_scratch.md
new file mode 100644
index 0000000..2bed7bc
--- /dev/null
+++ b/md/writeup/create_elf_file_from_scratch.md
@@ -0,0 +1,187 @@
+title:Create ELF file from scratch
+keywords:elf,linux
+
+# Create ELF file from scratch
+## Creating smallest possible elf file.
+
+### Structure of ELF file:
+Elf header  
+Program header  
+Code Part  
+Data Part  
+
+C structure of ELF header /usr/include/elf.h:
+
+```c
+typedef struct
+{
+  unsigned char e_ident[EI_NIDENT]; /* Magic number and other info */
+  Elf64_Half    e_type;             /* Object file type */
+  Elf64_Half    e_machine;          /* Architecture */
+  Elf64_Word    e_version;          /* Object file version */
+  Elf64_Addr    e_entry;            /* Entry point virtual address */
+  Elf64_Off     e_phoff;            /* Program header table file offset */
+  Elf64_Off     e_shoff;            /* Section header table file offset */
+  Elf64_Word    e_flags;            /* Processor-specific flags */
+  Elf64_Half    e_ehsize;           /* ELF header size in bytes */
+  Elf64_Half    e_phentsize;        /* Program header table entry size */
+  Elf64_Half    e_phnum;            /* Program header table entry count */
+  Elf64_Half    e_shentsize;        /* Section header table entry size */
+  Elf64_Half    e_shnum;            /* Section header table entry count */
+  Elf64_Half    e_shstrndx;         /* Section header string table index */
+} Elf64_Ehdr;
+```
+
+Structure of Program header file /usr/include/elf.h:
+
+```c
+typedef struct
+{
+  Elf64_Word    p_type;         /* Segment type */
+  Elf64_Word    p_flags;        /* Segment flags */
+  Elf64_Off     p_offset;       /* Segment file offset */
+  Elf64_Addr    p_vaddr;        /* Segment virtual address */
+  Elf64_Addr    p_paddr;        /* Segment physical address */
+  Elf64_Xword   p_filesz;       /* Segment size in file */
+  Elf64_Xword   p_memsz;        /* Segment size in memory */
+  Elf64_Xword   p_align;        /* Segment alignment */
+} Elf64_Phdr;
+```
+
+This structures is all what we need to make our ELF file.
+Now we will look inside kernel source and see that
+we need only one program header for our program. All big programs
+using usually two program headers one for code and one for data.
+
+/linux-3.3.1/fs/binfmt_elf.c:605
+
+```c
+if (loc->elf_ex.e_phnum < 1 ||
+    loc->elf_ex.e_phnum > 65536U / sizeof(struct elf_phdr))
+    goto out;
+```
+
+Step by step there should be filled all
+fields of the ELF header structure.
+
+```c
+typedef struct
+{
+  unsigned char e_ident[EI_NIDENT]; /* default values of ELFMAG,ELFCLASS64,ELFDATA2LSB */
+  Elf64_Half    e_type;             /* we making executable then it would be ET_EXEC  */
+  Elf64_Half    e_machine;          /* Architecture is 0x3e(EM_X86_64) 
+                                     (not from elf header 
+                                     from /binutils/include/elf/common.h) */
+  Elf64_Word    e_version;          /* Object file version EV_CURRENT */
+  Elf64_Addr    e_entry;            /* Entry point virtual address points to
+                                     main function it is with label entrypoint */
+  Elf64_Off     e_phoff;            /* Program header table file offset */
+                                      offset of program header sizeof(Elf64_Ehdr)
+  Elf64_Off     e_shoff;            /* Section header table file offset 
+                                        there is no section header */
+  Elf64_Word    e_flags;            /* No processor-specific flags 
+                                        */
+  Elf64_Half    e_ehsize;           /* ELF header size in bytes 
+                                        0x40 sizeof(Elf64_Ehdr)
+  Elf64_Half    e_phentsize;        /* Program header table entry size 
+                                        0x38 sizeof(Elf64_Phdr) */
+  Elf64_Half    e_phnum;            /* Program header table entry count 
+                                        0x01 */
+  Elf64_Half    e_shentsize;        /* Section header table entry size 
+                                        I put 0x40 */
+  Elf64_Half    e_shnum;            /* Section header table entry count 
+                                        0x00 */
+  Elf64_Half    e_shstrndx;         /* There is no section header and 
+                                     string table index is 0x0 then */
+} Elf64_Ehdr;
+```
+
+With program header we will tell kernel how to load our file in memory
+and with part of file will be mmaped to needed address. As our data
+and code is placed in one address space and kernel ELF source says
+that there is enough with 1 program header then we will use only 1.
+
+```c
+typedef struct
+{
+  Elf64_Word    p_type;         /* Segment type PT_LOAD */
+  Elf64_Word    p_flags;        /* Segment flags PF_X,PF_R,PF_W
+                                as our memory should be readable, writable and
+                                executable as it contains code and data */
+  Elf64_Off     p_offset;       /* Segment file offset 
+                                    point to offset of entry point label offset
+                                    in file */
+  Elf64_Addr    p_vaddr;        /* Segment virtual address 
+                                    64bits programs is usually at 0x400000+code_file_offset*/
+  Elf64_Addr    p_paddr;        /* Segment physical address 
+                                    same as above*/
+  Elf64_Xword   p_filesz;       /* Segment size in file 
+                                    size of code and data if file */
+  Elf64_Xword   p_memsz;        /* Segment size in memory 
+                                    same as above */
+  Elf64_Xword   p_align;        /* Segment alignment 
+                                    same as all programs have on my CPU*/
+} Elf64_Phdr;
+```
+
+Now everything is ready. Only thing that is left is code some small code
+that uses data. And it would be hello world
+
+```asm
+mov eax, 1
+mov edx, 12
+mov rsi, qword 0x040009c ;address of string 
+mov edi, 1
+syscall
+ 
+xor edi, edi
+mov eax, 60
+syscall
+ 
+msg db 'Hello World',0xA
+```
+
+To calculate offsets of code and data labels is used macro:
+
+```asm
+macro doffset
+{   
+    bits = 16
+    display ' 0x'
+    repeat bits/4
+        d = '0' + $ shr (bits-%*4) and 0Fh
+        if d > '9'
+            d = d + 'A'-'9'-1
+        end if
+        display d
+    end repeat
+    display 13,10
+}
+```
+
+
+Total size of executable on 64bit system:
+ELF header size 0x40  
+Program header 0x38  
+Code size 0x24  
+Data size 0xc  
+Total: 168 bytes  
+
+If 32 bit system is used then need to find definitions of data structures
+and retype some bytes. Also architecture variable need to be changed.
+
+## Future plans:
+Add some shared libs and compile smallest possible program using
+SDL graphics lib.
+
+## Code
+Code is written and tested on x86_64.
+
+
+
+## Links
+http://refspecs.freestandards.org/elf/elf.pdf  
+
+## Source
+
+http://archive.main.lv/files/writeup/create_elf_file_from_scratch/small_elf_file.zip  
\ No newline at end of file
diff --git a/md/writeup/gdb_helper_functions.md b/md/writeup/gdb_helper_functions.md
index e69de29..5fc45af 100644
--- a/md/writeup/gdb_helper_functions.md
+++ b/md/writeup/gdb_helper_functions.md
@@ -0,0 +1,224 @@
+title:Notes on videos
+keywords:math,statistics
+
+# GDB helper functions
+
+```text
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                              GDB helper functions                            +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                    INDEX                                     +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+1. Intro
+2. Source
+3. First run
+4. Breakpoints
+5. Registers
+6. Helper commands
+7. ToDo
+8. Links
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                     1.Intro                                  +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+GDB is GNU debugger. It comes as standard tool in gcc toolchain and all distros 
+have it as package. It work on all arch'es that gcc supports and it also can be 
+used as remote debugger. To debug it uses Linux kernel debugging functionality 
+of ptrace. For first moment its quite confusing tool too many command to type 
+and it doesn't have GUI or TUI. 
+
+What here will be added is command to show XMM registers, general purpose 
+registers and eflags with one command. This command make gdb more fun tool
+to use. 
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                    2.Source                                 +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+You can find GDB source here http://ftp.gnu.org/gnu/gdb/
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                   3.First run                                +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+For first run we have example of program that just prints some string and
+that's all. If you just run program with debugger and you haven't given commands
+to debugger it will run program as expected if everything is OK with program. 
+
+SOURCE: main1.c
+
+#include 
+
+{	
+	printf("Works fine\n");
+}
+ 
+
+Firs run is 
+	
+	gdb ./main1
+
+then in gdb command line type
+
+	(gdb) run
+
+And it will show 
+
+	Starting program: main1
+	Works fine
+	[Inferior 1 (process XXX) exit normally]
+
+String "Works fine" comes from printf's. And as everything was alright with
+program its terminated "normally". Lets start to go deeper in debugging things.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                  4.Breakpoints                               +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+Now lets use break points first breakpoint when to see whats happens in 
+program is set at main/_start function of C program as its start point
+of program. If program is written in assembler then there could be no
+main function like in C but still there entry point to program. And 
+possible why how to get address of entry point(main/_start) to program is
+with readelf utility
+
+	>readelf -h ./main1 | grep Entry
+
+    Entry point address:               0x400410
+
+Setting breakpoint to main function first way is just
+
+	>gdb ./main1
+	(gdb)break main
+	Breakpoint 1 at 0x40050a
+	(gdb)run
+	Start program: ./main1
+	Breakpoint 1, 0x040050a in main()
+
+Now we called C main function and stopped at needed location.
+Entry point is different in C it could be settuped directly with address or
+	
+	(gdb) break _start
+
+breakpoint on address
+
+	(gdb) break *0x400410
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                   5.Registers                                +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+Moment when you need debugger is when something "broken" here is example
+situation of broken code.
+
+SOURCE: main2.c
+
+int main()
+{ 
+	int i;
+
+	i = i/0;
+}
+
+Run until it break and see what happened
+	
+	gdb ./main2
+	(gdb) run
+	Program received signal SIGFPE
+	(gdb) display/i $pc
+	=> 0x4004c3 :  idiv   %ecx
+
+
+when number is divided on zero CPU usually generates exception and stops
+program showing that something bad is happened. 
+
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                6.Helper commands                             +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+To improve your experience there could be written macroses that can improve
+your experience with gdb. There is example of gdb macroses that could be useful
+and if you want to use them you can put gdbalias file at same directory as 
+debugged file and load from gdb with
+	
+	(gdb)source gdbalias
+
+shr32        - show 32 bit general purpose registers
+shr32a       - show 32 bit registers with 16, 8 bit registers and system registers
+shr64        - show 64 bit general purpose registers
+shr64a       - show 64 bit registers and 32/16/8 bit equivalents
+shsse_float  - show xmm registers and its 4  32 bit float values
+shsse_double - show xmm registers and its 2  64 bit double values
+shsse_i8     - show xmm registers and its 16  8 bit integer values
+shsse_i16    - show xmm registers and its 8  16 bit integer values
+shsse_i32    - show xmm registers and its 4  32 bit integer values
+shsse_i64    - show xmm registers and its 2  64 bit integer values
+s            - one step in debugger
+flags        - show eflags
+showrchanges - on every step show changes from previous step
+sc           - one step and show changed registers
+
+All register could be printed with gdb command 
+
+	printf
+
+registers name that are used is $rax, $eax, $ax, $ah, $al and all others
+
+shsee commands are showing xmm0 registers and what is inside depends
+on you interpretation that why there is 8 registers
+
+	$xmm0,$xmm1,$xmm2,$xmm3,$xmm4,$xmm5,$xmm6,$xmm7
+
+and values depended on interpretation can be accessed as 
+
+X - register index, Y - array index
+
+	$xmmX.v4_float[0]
+	$xmmX.v2_double[0]
+	$xmmX.v16_int8[0]
+	$xmmX.v8_int16[0]
+	$xmmX.v4_int32[0]
+	$xmmX.v2_int64[0]h
+
+Changes on each step are made just by saving registers:
+
+	set $oldrax = $rax
+
+and when changes happens if/else:
+
+	if ($rax != $oldrax)
+		printf "RAX:0x016lX ", $rax
+	end
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                     7.ToDo                                   +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+Add more descriptions and more basic topics how to use gdb
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                     8.Links                                  +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+[1] http://ftp.gnu.org/gnu/gdb/  
+[2] https://en.wikipedia.org/wiki/GNU_Debugger  
+[3] https://github.com/gdbinit/Gdbinit/blob/master/gdbinit  
+[4] https://sourceware.org/gdb/onlinedocs/gdb/Define.html  
+[5] https://github.com/FreeArtMan/gdbalias  
+[6] http://www.delorie.com/gnu/docs/gdb/gdb_28.html  
+[7] http://www.delorie.com/gnu/docs/gdb/gdb_29.html  
+```
+## Downloads
+
+http://archive.main.lv/files/writeup/gdb_helper_functions/gdbalias
+
diff --git a/md/writeup/microbbs_minimalistic_bbs_system.md b/md/writeup/microbbs_minimalistic_bbs_system.md
new file mode 100644
index 0000000..4f7b8a1
--- /dev/null
+++ b/md/writeup/microbbs_minimalistic_bbs_system.md
@@ -0,0 +1,76 @@
+title:Notes on videos
+keywords:math,statistics
+
+# MicroBBS minimalistic BBS system
+
+
+```text
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                    MicroBBS                                  +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                    INDEX                                     +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ 1. Intro
+ 2. Goal
+ 3. Usage
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                     1.Intro                                  +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+MicroBBS is attempt to write basic plain BBS that could be run on Linux/BSD 
+systems on any kind of hardware. Also minimal dependencies should be used. No 
+scripting, no databases, no external libraries as dependencies. Everything 
+should be self-sufficient and easily compiled and lunched.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                     2.Goal                                   +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+basic chat
+article publishing
+file sharing
+message board
+maybe door-games
+
+No extra stuff and extra super mega features. Also i have downloaded
+old BBS sources and try to write everything in old school style =). Now
+its is only 14kb and 50 more kb to go. And yes i will try not to go over
+64kb size of executable.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                     3.Usage                                  +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+Not alot works now just some picture shows and one article could be readed.
+Its still in alfa stage.
+
+Type in shell:
+
+microbbs
+
+And bbs should run in your terminal. You can put it as default shell for ssh
+
+
+
+
+
+
+Links
+https://github.com/FreeArtMan/microbbs
+
+```
+
+## Downloads
+
+
+
+microbbs-0.1.7.tar.gz - 
+6KiB -  
+http://archive.main.lv/files/writeup/microbbs_minimalistic_bbs_system/microbbs-0.1.7.tar.gz  
+microbbs-0.2.2.tar.gz -
+49KiB - 
+http://archive.main.lv/files/writeup/microbbs_minimalistic_bbs_system/microbbs-0.2.2.tar.gz
diff --git a/md/writeup/serial_gps_data_reading_utility.md b/md/writeup/serial_gps_data_reading_utility.md
new file mode 100644
index 0000000..b3d233f
--- /dev/null
+++ b/md/writeup/serial_gps_data_reading_utility.md
@@ -0,0 +1,88 @@
+title:Serial GPS data reading utility
+keywords:gps,serial,uart,tty
+
+# Serial GPS data reading utility
+Serial usb gps deviceses can be used trought serial consoles
+or some other libraries. From shell need some basic configuaration
+at begining to use serial device from shell. This command
+provide simple way how to do it.
+This code opens /dev/tty* device, setup baud rate to 4800
+and outputs line by line recieved data.
+When device connected ther could be that is not in NMEA mode
+it could be switched with:
+
+```
+gpsctl -n /dev/ttyUSB0
+```
+
+Then you can connect with it with some serial terminal(dont forget baudrate
+could be 4800 or 9600):
+
+```
+minicom -D /dev/ttyUSB0
+```
+
+Now we can use our gpsr utility
+
+```
+./gpsr -d /dev/ttyUSB0 -c 0
+./gpsr -d /dev/ttyACM0 -c 1
+```
+
+NMEA format is csv like and it easyly can be used from shell. Here is
+exmple how it looks:
+
+```
+$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A
+```
+
+Where:
+RMC Recommended Minimum sentence C
+123519 Fix taken at 12:35:19 UTC
+A Status A=active or V=Void.
+4807.038,N Latitude 48 deg 07.038' N
+01131.000,E Longitude 11 deg 31.000' E
+022.4 Speed over the ground in knots
+084.4 Track angle in degrees True
+230394 Date - 23rd of March 1994
+003.1,W Magnetic Variation
+*6A The checksum data, always begins with *
+
+Get time from GPS
+
+```
+./gpsr -d /dev/ttyUSB0 -c 100 | stdbuf -o0 grep -w "GPRMC" | cut -d',' -f2
+```
+
+## REQUIREMENTS
+GCC C, minicom, shell, GPS device
+
+## TESTED
+I have tested everything with GPS devices BU-353 and with
+some device that havenot any visual marks but have chip
+from u-blox manufacturer.
+
+## COMPILE:
+
+```
+gcc buf.c -c
+gcc serial_tty.c -c
+gcc serial_tty.o buf.o gpsr.c -o gpsr
+```
+
+## TODO:
+there could be added baudrate set as params
+loging in csv,xml,json files
+make longterm test for stability
+
+
+## Links
+http://en.wikipedia.org/wiki/NMEA_0183  
+http://www.gpsinformation.org/dale/nmea.htm  
+http://home.mira.net/~gnb/gps/nmea.html  
+http://linux.die.net/man/1/minicom  
+
+## Downloads
+gpsr.tar.gz - 3KiB -
+http://archive.main.lv/files/writeup/serial_gps_data_reading_utility/gpsr.tar.gz
+