sb: notes

Author: amorriscode

data/second-brain/Address Space Layout Randomization.md

@@ -0,0 +1,3 @@
+[[operating system]]
+# Address Space Layout Randomization
+- Randomizing memory addresses so attackers can't reliably predict memory addresses they need to target to exploit it

data/second-brain/CS Primer - Operating systems.md

@@ -28,5 +28,39 @@
 	- System call transfers control into the OS while raising the hardware privilege level
 - User apps run in "user mode"
 	- Hardware restricts what apps can do
-
-## CPU Timing
+### Stack Overflow
+- Stack is a memory region allocated by the OS
+	- Overflowing it, you try to write to memory _outside_ the region where you don't have permission
+- OS raises a segfault due to the illegal memory address
+	- It doesn't know what the cause of the segfault is which is why you don't get an actual stack overflow error
+- Historically the heap was started at low addresses, stack at high addresses
+	- The big gap in the middle maximized the space available before collision
+	- Doesn't matter anymore thanks to enormous virtual address space
+- What contributes to the size of a stack frame?
+	- Data
+	- Return address
+	- Rounding up to alignment boundaries
+		- Usually 16 bytes on modern systems
+		- Helps with performance
+- You can't map all the virtual address space to actual hardware
+- [[Address Space Layout Randomization]]
+- Programs can request an increase to their stack limit with `setrlimit`
+	- You can raise your soft limit up to the hard limit but only root can raise hard limits
+	- `getrlimit` to check limits
+- Threads get their own stack to avoid collissions
+- `vmmap`
+	- Virtual size --> how much address space is reserved for the stack
+	- Resident size --> how much physical RAM is being used
+- Demand paging
+	- Declaring an array doesn't allocate physical RAM, you have to write to the memory
+	- OS maps physical memory when you touch it
+## Byte write
+- File systems don't track individual bytes on disk
+	- Space is allocated in fixed-size chunks (blocks)
+	- Blocks are usually 4096 bytes (4 KiB)
+	- Writing 1 byte still gets a 4 KiB block
+- Larger blocks === less bookkeeping overhead but more wasted space
+- `/dev/urandom` is an interface to the kernel's random number generator
+- File descriptor is a "handle" to an open file
+	- More efficient for accessing a file (open once)
+	- Keeps state (position tracking, etc.)

data/second-brain/Comic Reading List.md

@@ -24,6 +24,7 @@
 - Exquisite Corpses #5
 - Falling in Love on the Path to Hell #10
 - Frieren vol 12
+- Harley and Ivy #1
 - Imperial #1
 - It Killed Everyone But Me #1
 - Kaya #11

data/second-brain/Introduction to Ancient Greek History.md

@@ -110,7 +110,7 @@
 - Hoplite phalanx
 	- "Shield roller" (rough etymology) 
 	- Core infantry in a solid block
-	- Changed society because men started fighting together (no mo heroes) and started demanding equal politic rights
+	- Changed society because men started fighting together (no more heroes) and started demanding equal politic rights
 	- Heavy armour
 	- Only citizens who can afford the equipment can fight
 - Shield design protects the man to the left, strong together
@@ -120,5 +120,4 @@
 	- Fighting for their city
 - The honour code has moved from the individual to the whole (polis)
 - Colonization begins due to a need for new farmland
-- Colonization allowed Greeks to start learning/adopting more from other civilizations
-- 
+- Colonization allowed Greeks to start learning/adopting more from other civilizations

data/second-brain/call stack.md

@@ -1,8 +1,6 @@
+[[Computer Science]]
 # Call Stack
-
 - Used to keep track of function calls during program execution
-  - Stores all the variables required for the function
+	- Stores all the variables required for the function
 - A [[stack]] [[data structure]]
 
-[[Computer Science]]
-

data/second-brain/data structure.md

@@ -0,0 +1,2 @@
+[[computer science]]
+# Data structure

data/second-brain/derek-parfit.md

@@ -1,2 +1,3 @@
+[[philosopher]]
 # Derek Parfit
-
+- Specialized in personal identity, [[rationality]], and [[ethics]]

data/second-brain/e-ubc.md

@@ -0,0 +1,2 @@
+[[philosophy]]
+# Rationality