Prospero system library layout and privilege model

The retail filesystem organisation of system shared libraries (.sprx), the sandbox partition boundaries, and the four-tier privilege model governing access on the Prospero-generation platform (firmware 12.40).

Everything below is measured from retail hardware via obSCEne runtime probes and live filesystem inspection. The complete module list is the companion manifest data/hardware/ps5-sprx-manifest.tsv, a measured snapshot at firmware 12.40 and the source of truth for the per-tier tallies below, which move with firmware.

1. Divergence from the Orbis-generation platform

On the Orbis-generation platform, system shared libraries resided almost exclusively in a single flat directory: /system/common/lib/. Any library not shipped in /system/common/lib/ was bundled with the application inside /app0/sce_module/ (such as libc.prx or libSceFios2.prx).

On the Prospero-generation platform, the vendor compartmentalized the system filesystem into distinct mount points with independent access controls, security tokens, and sandbox rules:

/ (Root)
├── /system/common/lib/            [Tier: app]        Standard Title Sandbox
├── /system_ex/common_ex/lib/      [Tier: system]     System Apps & WebKit
├── /system/priv/lib/              [Tier: root]       Privileged Daemons & Core Codecs
└── /app0/sce_module/              [Tier: app/title]  Application-Bundled Modules (*.prx)

Linking a module statically via DT_NEEDED forces the system loader (rtld) to resolve it at launch. If that library does not exist in /system/common/lib/ or is in a higher privilege tier denied to the title, the process is terminated before executing a single instruction.

2. The four privilege tiers

Access to system libraries is partitioned into four permission tiers (D296):

Tier Category / Target Typical Directory Credentials (paid) Scope & Capabilities
app Game title ("gd") /system/common/lib/ 0x3800000000000000
0x3100000000000002		 Standard sandboxed game titles. Access to the standard application-tier SPRXs and /app0/sce_module/*.prx.
sysmodule Title with sysmodules Dynamic via IPC Same as app Dynamically activated into process address space via sceSysmoduleLoadModule(id) / SceSysCore.
system System App ("system_app") /system_ex/common_ex/lib/ 0x3800000000000001 Extended system applications (WebKit, Shell UI, Settings, Media Player). Access to WebKit, Mono, and POSIX runtimes.
root System Service / Daemon /system/priv/lib/ 0x8000000000000001 Privileged system services and jailbroken payloads. Access to proprietary hardware encoders and kernel services.

3. Directory layout and module breakdown

3.1 /system/common/lib/ (standard application tier)

Mapped into every standard game title sandbox (appCategory: "gd"); the manifest lists these SPRXs as a measured snapshot. These libraries provide the public and semi-public APIs exposed to games:

3.2 /system_ex/common_ex/lib/ (extended system tier)

Mounted only for applications flagged as system applications (system_app / 0x3800000000000001). Sandboxed game titles cannot access this directory. As measured, it holds native C/C++ libraries alongside a larger set of Mono/.NET assemblies (.dll.sprx); the manifest carries the exact split:

3.3 /system/priv/lib/ (root / privileged tier)

Accessible only to processes with root/kernel daemon credentials (0x8000000000000001 or specific daemon entitlements); the manifest lists these privileged SPRXs as measured. Unprivileged titles attempting to load these fail with permission denials:

4. Key differences, Orbis versus Prospero

Library / Functionality Orbis Prospero Impact on Homebrew
libScePosix /system/common/lib/libScePosix.sprx /system_ex/common_ex/lib/libScePosixForWebKit.sprx Titles cannot statically link libScePosix. Must resolve dynamically via obs_module_open.
libSceVencCore Present in /system/common/lib/ Absent (merged into libSceVenc.sprx) Static DT_NEEDED on libSceVencCore aborts launch with val 2 (ENOENT).
3D Rendering libSceGnmDriver.sprx libSceAgc.sprx / libSceAgcDriver.sprx Native titles use AGC; GnmDriver is retained for backwards compatibility.
Audio Encoders Broadly accessible Strictly isolated in /system/priv/lib/ Dolby/DTS encoders require root privilege.
C Runtime Bundled in /app0/sce_module/libc.prx Built into /system/common/lib/libSceLibcInternal.sprx Requiring libc.prx via .libc_param causes SCE_KERNEL_ERROR_ESDKVERSION if versions mismatch.

5. obSCEne probing strategy

obSCEne treats module presence as an empirical question, probed dynamically rather than assumed:

  1. Static dynamic section (DT_NEEDED): obscene.eboot.elf statically links only a bounded set of core libraries guaranteed to exist in /system/common/lib/ on every Prospero firmware, gated by EBOOT_LIBS because a system loader resolves every named library before any of the probe's code runs (D226). The set is the behavioural imports in src/probe/imports.c and the per-target exclusions there; read that file for the current membership.
  2. On-demand loader (obs_module_open): Non-essential libraries (POSIX, video encoders, system tools) are resolved at runtime with obs_module_open(), which searches the tier paths in order of accessibility.
  3. Privilege flag (--privilege): selfish container builds declare target privilege (app, sysmodule, system, root), generating the matching paid auth token and appCategory so probes test higher tiers when executing under kstuff (D296).
  4. Census logging (OBS|modtier|...): The runtime module probe emits the verified permission tier of every reachable module into the report for automated comparison.

6. Application category, display arbitration, and memory budgets

Process authority and runtime hardware resources are governed across two orthogonal axes:

  1. Privilege tier (paid in SELF header): Determines kernel authority, raw device access, sysctls, and directory partition traversal (/system/priv/lib/).
  2. Application category (applicationCategoryType in param.json): Determines display bus ownership (SceSysAvControl), Direct Memory budget (ResourceArbitrator), and UI focus:
    • 0 (SCE_APP_CATEGORY_TYPE_BIG_APP / gd / native_game): Primary foreground application.
    • 65536 (0x00010000, SCE_APP_CATEGORY_TYPE_SYSTEM_APP): Background or system application.
    • 131072 (0x00020000, SCE_APP_CATEGORY_TYPE_MINI_APP): Mini app (quick menu overlay).

6.1 Hardware display and memory arbitration rules

6.2 The Big App PRX loader contract

When launched as category 0 (native_game), the Prospero runtime dynamic linker (rtld) activates the retail game startup contract:

6.3 Homebrew configuration matrix

Target Goal Application Category Privilege (paid) Bundled sce_module/ Suitable Use Cases
GUI / Game / Emulator / Screen Output 0 (Big App) root or app Required: libc.prx (Gen-4 container, 4F 15 3D 1D) Emulators, games, graphical homebrew, full obSCEne visual tests.
Headless Daemon / Background Service 65536 (0x10000) root or system Not required FTP servers, telnet/shsrv daemons, headless klog dumpers.
System Overlay / HUD 131072 (0x20000) system System app standard On-screen displays, quick menus, notification overlays.