11 Appendix C: Loot System Internals

This appendix documents the internal workings of BL4’s loot system, based on memory analysis and game file extraction.

11.1 Loot Pool Architecture

11.1.1 Core Classes

Class	Description
ItemPoolDef	Defines a loot pool
ItemPoolEntry	Single item in a pool
ItemPoolListDef	List of multiple pools
ItemPoolSelectorDef	Selection logic
ItemPoolInstanceData	Runtime instance data
ItemPoolSelectorStateDef	Selection state

Script path: /Script/GbxGame.ItemPoolDef

11.1.2 Pool Types Enum

enum class ELootPoolTypes {
    All = 0,
    BaseLoot = 1,
    AdditionalLoot = 2,
    DedicatedDrops = 3,
    GearDrivenDrops = 4,
    MAX = 5
};

11.2 Rarity Tiers

11.2.1 Tier Definitions

Tier	Component ID	Material Path
Common	comp_01_common	DA_MD_BOR_Common
Uncommon	comp_02_uncommon	DA_MD_BOR_Uncommon
Rare	comp_03_rare	DA_MD_BOR_Rare
Epic	comp_04_epic	DA_MD_BOR_Epic
Legendary	comp_05_legendary	DA_MD_BOR_Legendary_01

Material path pattern: /Game/Gear/Weapons/_Shared/Materials/BOR/DA_MD_BOR_{Rarity}

11.2.2 Price Modifier Attributes

Tier	Attribute
Common	attr_calc_pricemod_rarity_common
Uncommon	attr_calc_pricemod_rarity_uncommon
Rare	attr_calc_pricemod_rarity_rare
Epic	attr_calc_pricemod_rarity_epic
Legendary	attr_calc_pricemod_rarity_legendary

11.3 Loot Weight System

11.3.1 Weight Properties

Property	Description
GrowthExponent	Level scaling exponent
BaseWeight	Base drop weight
GameStageVariance	Variance by game stage
RelativeGameStage	Relative stage modifier
GameStageTable	Stage lookup table
LootGameStages	Game stages for loot
RankLootRarityTable	Rarity by rank table

11.3.2 Weight Classes

Class	Description
RarityWeightData	Weight configuration
LocalRarityModifierData	Local rarity modifiers

11.4 Luck System

11.4.1 Core Classes

Class	Description
LootGlobalsDef	Global loot settings
LuckCategoryAttribute	Luck category attribute
LuckCategoryAttributesState	Runtime luck state
LuckCategoryDef	Luck category definition
LuckCategoryValueResolver	Resolves luck values
LuckGlobals	Global luck settings

11.4.2 Luck Categories

Category	Description
LuckCategories	Base luck modifiers
EnemyBasedLuckCategories	Per-enemy modifiers
PlayerBasedLuckCategories	Player-specific modifiers

11.5 Drop Probability Tables

11.5.1 Dedicated Drop Probability (Struct_DedicatedDropProbability)

Tier	Probability
Primary	20% (0.2)
Secondary	8% (0.08)
Tertiary	3% (0.03)
Quaternary	0% (0.0)
Shiny	1% (0.01)
TrueBoss	0% (0.0)
TrueBossShiny	0% (0.0)

11.5.2 Enemy Drops (Struct_EnemyDrops)

Fields (DoubleProperty type):

Field	Description
Guns_Probability	Chance to drop guns
Guns_HowMany	Number of guns
Shields_Probability	Shield drop chance
Shields_HowMany	Number of shields
GrenadesOrGadgets_Probability	Grenade/gadget chance
GrenadesGadgets_HowMany	Number to drop
ClassMods_Probability	Class mod chance
ClassMods_HowMany	Number of class mods
RepKits_Probability	Repair kit chance
RepKits_HowMany	Number of repair kits
Enhancements_Probability	Enhancement chance
Enhancements_HowMany	Number of enhancements
CurrencyOrAmmo_Probability	Currency/ammo chance
CurrencyAmmo_HowMany	Amount
EXP_Multiplier	Experience multiplier
Rarity_Modifier	Rarity boost

11.6 Known Item Pools

11.6.1 Boss Pools

Pool	Description
ItemPoolList_Enemy_BaseLoot_Boss	Standard boss drops
ItemPoolList_Enemy_BaseLoot_BossRaid	Raid boss drops
ItemPoolList_ShatterlandsCommanderFortress_TrueBoss	True Boss
ItemPoolList_Timekeeper_TKBoss_TrueBoss	Timekeeper True Boss

11.6.2 Rarity Pools

Pool	Description
itempool_guns_01_common	Common weapons
itempool_guns_02_uncommon	Uncommon weapons
itempool_guns_03_rare	Rare weapons
itempool_guns_04_epic	Epic weapons
itempool_guns_05_legendary	Legendary weapons

11.6.3 Special Pools

Pool	Description
ItemPool_FishCollector_Reward_Legendary	Fish collector reward
ItemPool_BlackMarket_Comp_BOR_HW_DiscJockey	Black Market
ItemPool_BlackMarket_Comp_BOR_HW_Streamer	Black Market

11.7 Lootable Objects

11.7.1 Classes

Class	Description
GbxCondition_CanOpenLootable	Open condition check
GbxCondition_ShouldLootableShowLockedPrompt	Lock prompt
LootableObjectInstanceProxy	Instance proxy
LootableObjectBehaviorMod	Behavior modifier
LootableObjectBodySettings	Body settings
LootableObjectBodyState	Runtime body state

11.8 Inventory System

11.8.1 Core Classes

Class	Description
InventoryParam	Inventory parameter
InventoryParamsDef	Parameter definitions
InventoryRarityDataTableValueResolver	Rarity resolver
InventoryRarityDef	Rarity definition
InventorySerialNumber	Item serial number
InventoryStatsContainer	Stats container
InventoryStatsPropertyResolver	Stats resolver
InventoryStatTags	Stat tags
InventoryStatAttribute	Stat attribute

11.8.2 Key Class: InventoryRarityDataTableValueResolver

This class resolves rarity values from DataTables. Potential patching target for forcing specific rarity tiers.

11.9 RNG Implementation

11.9.1 Import Table Functions

Address	Function	DLL
0x150b74e18	std::_Random_device	MSVCP140.dll
0x150b75050	BCryptGenRandom	bcrypt.dll
0x150b759d0	rand	api-ms-win-crt-utility-l1-1-0.dll
0x150b759d8	srand	api-ms-win-crt-utility-l1-1-0.dll

11.9.2 RDRAND Usage

108 RDRAND instructions found in the binary. These are hardware RNG entry points.

Pattern: 0F C7 F0 (rdrand eax)

11.10 Memory Addresses

11.10.1 FName Locations

Region	Description
0x05b25000-0x05f96000	Class/struct names
0x1cd44000-0x1cd55000	Property/field names

11.10.2 Specific Addresses

Data	Address	Notes
ItemPoolDef class	0x5b25150	Class definition
Pool types enum	0x65610d50	ELootPoolTypes
Rarity tiers	0x79105c0	Tier definitions
Weight properties	0x1cd44680	Weight data
Luck classes	0x5f955e0	Luck system
Legendary items	0x94e7870	Item database

11.11 Loot Chance System

11.11.1 DataTable Structure

Found LootChanceDefinedValueRow for configuring loot chances.

Class	Description
LootChanceDefinedValueRow	DataTable row for chances
GetSummary_Chance	Chance summary function

11.12 Stat Modifiers

11.12.1 From Extracted Data

Stat	Description
Damage_Scale	Base damage multiplier
Damage_Value	Flat damage value
CritDamage_Add	Critical damage bonus
FireRate_Scale	Fire rate multiplier
FireRate_Value	Fire rate value
ReloadTime_Scale	Reload speed modifier
ElementalChance_Scale	Element proc chance
Accuracy_Scale	Accuracy modifier
Spread_Scale	Spread modifier
Recoil_Scale	Recoil modifier

11.13 Injection Approaches

11.13.1 LD_PRELOAD Method (Linux/Proton)

Intercept RNG at syscall level:

# Bias RNG for better drops
LD_PRELOAD=/path/to/libbl4_preload.so BL4_RNG_BIAS=max ./game

This intercepts getrandom() and similar syscalls.

11.13.2 Direct Memory Patching

Target locations for modification:

Template	Target	Address
dropRate	RarityWeightData	0x5f9548e
dropRate	BaseWeight	0x6f3a44c4
dropRate	GrowthExponent	0x6f3a44b4
luck	LuckGlobals	0x5f95658
luck	LuckCategories	0x6f3a4560

11.13.3 Implementation Strategy

Find live InventoryRarityDataTableValueResolver instances
Locate float weight values in DataTable
Patch weights to favor legendary tier
Or patch comparison code for weight threshold

11.14 Extracted Items Database

Located at share/manifest/items_database.json:

Content	Count
Item pools	62
Balance items	26
Stat types	73

11.14.1 Sample Pools

ItemPoolList_Enemy_BaseLoot_Boss
ItemPoolList_Enemy_BaseLoot_BossRaid
itempool_guns_01_common
itempool_guns_04_epic
ItemPool_FishCollector_Reward_Legendary

11.14.2 Generate Database

bl4-research items-db -m share/manifest

11.15 Binary Protection

The executable uses protection (likely Denuvo):

No exports (stripped)
References Borderlands4.pdb but PDB not included
Heavy obfuscation (XOR, NOT, RCL patterns)
Runtime analysis more effective than static

Warning

Static binary analysis is difficult. Runtime analysis via memory attachment is recommended.

Data from live memory analysis using bl4 memory tool.