C-Systems on The VikiD Truth

objdump

Sun, 04 Jun 2023 00:49:00 +0400

objdump

The truth behind every program you run: it is just bytes, and those bytes are instructions you can read. objdump is the tool that turns the bytes back into something a human can follow.

What it is, in plain words

objdump is part of GNU binutils (along with as, ld, nm, readelf, strings). Point it at an object file, executable or shared library and it will show you:

the headers – what kind of file, which CPU, where it starts;
the sections – .text (code), .data, .rodata, .bss and friends;
the symbols – names of functions and variables;
the disassembly – machine code translated back into assembly mnemonics.

LLVM ships a near drop-in twin, llvm-objdump, with the same main flags.

Rust

Fri, 19 May 2023 23:18:13 +0400

Rust

Here is the truth Rust is built on: most bugs that crash systems and open security holes are memory bugs, and a compiler can stop nearly all of them – if you’re willing to talk to it about ownership. Rust is that conversation.

Odin

Mon, 05 Sep 2022 06:40:28 +0400

Odin

Here is the truth Odin is built on: most programs are about transforming data, so the language should make data obvious and get out of the way. No classes, no hidden allocations, no garbage collector – just a clean, modern take on what C was trying to be.

Zig Language

Tue, 30 Aug 2022 05:35:16 +0400

Zig Language

Here is the truth Zig is aimed at: C is still the lingua franca of systems, but its undefined behaviour, header files and build story are a tax everyone pays. Zig keeps C’s honesty about memory and lays that tax down.

The V Programming Language

Thu, 25 Aug 2022 02:35:41 +0400

The V Programming Language

Here is the truth about V: it wants to be the language you can learn in a weekend and ship with on Monday – Go’s simplicity, C’s speed, Rust’s safety goals, without the steepest parts of any of them. Whether it fully delivers depends on what you need, but the ambition is clear and the tooling is pleasant.

Using the C Debugger

Fri, 27 Aug 2021 01:41:01 +0400

Using the C Debugger

The GBD Tutorial, Online Docs

Compile your program with ‘-g’
```
gcc -g main.c
```
run gbd
```
gdb a.out
```
exit gbd
```
(gdb) quit
```

Common Commands

C Syntax

Fri, 27 Aug 2021 00:51:47 +0400

C Syntax

if (TEST) {
 CODE;
} else if(TEST) {
 CODE;
} else {
 CODE;
}

SWITCH

switch(OP) {
 case CONST:
 CODE;
 break;
 default:
 CODE;
}

cppreference:switch
WHILE
```
while(TEST) {
 CODE;
}
```

while(TEST){
 if(TEST2){
 continue;
 }
 CODE;
}

while(TEST){
 if(TEST2){
 break;
 }
 CODE;
}

DO
```
do {
 CODE;
} while(TEST)
```
FOR
```
for (INIT; TEST; POST) {
 CODE;
}
```
ENUM
```
 enum{CONST1, CONST2} NAME;
```
GOTO

if(TEST){
 goto somewhere
}
somewhere:
 CODE;

FUNCTION

TYPE NAME(ARG1, ARG2, ..) {
 CODE;
 return VALUE;
}

TYPEDEF
```
typedef DEF ID;
```
STRUCT
```
struct NAME {
 ELEMS;
} [VAR_NAME];
```

typedef struct [STRUC_NAME] {
 ELEMS;
} ID

UNION
```
union NAME {
 ELEMS;
}[VAR_NAME]
```

Operators

Fri, 27 Aug 2021 00:40:19 +0400

Operators

Operator tables for quick reference – arithmetic, assignment, bitwise, logical and relational. Pictures beat paragraphs when you just need to remember precedence. For deeper C notes see C Programming and Literals.

C Standard Library

Thu, 29 Jun 2017 02:39:49 +0400

C Standard Library

Here is the truth about the C standard library: it is a small, sharp toolkit – I/O, memory, strings, maths, time – that every hosted C program leans on, and its sharpest edges are still the string and unchecked I/O functions. Knowing what is in ISO C versus what your OS adds is half of reading real code.

Assembly Languagess

Wed, 30 Nov 2016 01:43:52 +0400

Assembly Languagess

Links, Sources and Reading List

Some Notes:

ebp is known as the base pointer or the frame pointer.

 1. On entry to your function, you push it (to save the value for the calling function).

 2. Then, you copy esp, the stack pointer, into ebp, so that ebp now points to your function's stack frame.

 3. At the end of your function, you then pop ebp so that the calling function's value is restored.

For some clarification on exactly what is going on -
the push instruction:

 1. puts the value from the specified register (ebp in this case), onto the stack, and
 2. decrements the stack pointer by the appropriate amount.

The pop operation is the opposite -

 1. it increments the stack pointer and takes a value from the stack and
 2. puts it in the specified register.

Characters in C Programming

Tue, 22 Nov 2016 22:10:31 +0400

Characters in C Programming

Here is the truth about characters in C: there are no characters – only small integers that we agree to draw as letters. 'A' is just the number 65 wearing a costume. Everything about text in C, from strings to Unicode, follows from that.

What it is, in plain words

The char type is C’s smallest addressable unit: exactly one byte (sizeof(char) is always 1, and on every mainstream system a byte is 8 bits). A character constant in single quotes, like 'A', is a number – the character’s code in the execution character set, which today is essentially always ASCII for the first 128 values.

Floating-point numbers in C Programming

Tue, 22 Nov 2016 22:09:53 +0400

Floating-point numbers in C Programming

Here is the truth that trips up every programmer once: 0.1 + 0.2 is not 0.3 on your computer – not in C, not in Python, not in JavaScript. Floating-point numbers are not real numbers; they are a clever, finite approximation of them, and knowing where the approximation leaks is the whole skill.

What it is, in plain words

C has three floating-point types:

Type	Usual format	Significant decimal digits	Range (approx.)
`float`	IEEE 754 binary32	~7	$10^{\pm 38}$
`double`	IEEE 754 binary64	~15–16	$10^{\pm 308}$
`long double`	80-bit x87 on x86 Linux, 128-bit on some ARM, same as `double` on Windows/MSVC	18–33	varies

A floating-point number is stored like scientific notation in base 2: a sign, an exponent, and a significand (mantissa).

Integers in C Programming

Tue, 22 Nov 2016 22:07:11 +0400

Integers in C Programming

Here is the truth about integers in C: an int is not a number in the mathematical sense – it’s a fixed number of bits, and the bits run out. Almost every integer bug in C comes from forgetting that.

What it is, in plain words

C has a family of integer types that differ in size (how many bits) and signedness (whether they can be negative):

Strings in C Programming

Tue, 22 Nov 2016 21:52:26 +0400

Strings in C Programming

Here is the truth about strings in C: there is no string type – only arrays of char that we agree end with a zero byte. Every convenience and every CVE in C text handling follows from that convention.

What it is, in plain words

A C string is a contiguous sequence of bytes ending in '\0'. The type used to point at one is char * (or const char * when you promise not to modify). The standard library in <string.h> and <stdio.h> provides the classic tools: strlen, strcpy, strncpy, strcmp, strcat, strchr, strstr, sprintf, snprintf.

Literals

Mon, 21 Nov 2016 22:08:27 +0400

Literals

Here is the truth about literals: they are how values show up in source code before they have a name. Every language has them; C’s are small, strict and easy to get subtly wrong – especially once suffixes and escape sequences enter.

What it is, in plain words

A literal is a notation that writes a value directly: 42, 3.14, 'a', "hello", true. In C (and C-like languages) the form of the literal decides its type and how it’s stored. Related pages cover each family in depth: integers, floats, characters, strings.

Objects in C

Mon, 21 Nov 2016 09:49:09 +0400

Objects in C

Here is the truth about “objects”: the word means different things in different traditions, and fights about OOP usually start from mixed definitions. In Smalltalk an object is a living entity that answers messages; in C++ it is a region of memory with a type; in JavaScript it is a mutable property bag with a prototype link.

What it is, in plain words

An object packages state (data) with behaviour (code that uses that data). Languages implement that idea differently:

Identifiers in C

Mon, 21 Nov 2016 05:40:07 +0400

Identifiers in C

Back to Tokens | Back to C Programming | The Compiler

There are 4 types of Identifiers and each type gets its own namespace.

Label Names, are names that end in a colon, :
Tags for structure, union, and enumeration types
Names of Structure or Union members
Ordinary Identifiers (all others)

struct tag { char tag; ...}

Here you can see we have created a structure with the tag tag, which also has a member tag of the type char.

The Compiler

Mon, 21 Nov 2016 04:06:50 +0400

Back to C programming

The Compiler

The C compiler translates C-source-code into machine code.

The Compiler translates each source file into an object file also known as a module.

If there are more that 1 object files, these are then linked by the linker which outputs a executable.

The executable is what we normally run as a program in the system.

The Translation Phases

The compilation takes place in 8 steps.

C Programming

Mon, 21 Nov 2016 03:47:35 +0400

C Programming

The C programming language is at the heart of GNU/Linux - it is the programming language most of the Linux Kernel and GNU tools is written in.

There are many outstanding books and online resources where you can learn C and as such this site will not try and duplicate these efforts.