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# LD Linker scripts
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The linker scripts in `esp-open-sdk/sdk/ld/` dictate how the GCC linker organizes code sections (`.text`, `.data`, `.bss`, `.irom0.text`) and maps them to physical flash offsets and memory addresses.
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### Understanding the Naming Conventions

  * **`v6`**: Refers to the version of Espressif's SDK linker layout definitions.
  * **`new` vs. `old`**: Refers to the Espressif bootloader structure version:
    * **`old` (v1.1 bootloader era):** Used legacy flash mapping rules (limited `irom0` size).
    * **`new` (v1.2+ bootloader era):** Expanded the mapped `irom0` size per application slot to support larger code bases.
  * **`512` / `1024` / `2048`**: Refers to the target flash size in **Kilobytes** (512 KB, 1 MB, 2 MB).
  * **`app1` vs. `app2`**: Used in **OTA (Over-The-Air)** two-slot layouts (`user1.bin` and `user2.bin`). `app1` links code to execute from the first flash partition, while `app2` links code to execute from the second partition.

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### Breakdown of the Linker Scripts

#### 1. Non-OTA Script

  * **`eagle.app.v6.ld`**: Purpose:** Non-OTA (No-Bootloader) applications. Maps `eagle.flash.bin` directly to offset `0x00000` and `eagle.irom0text.bin` to offset `0x10000` or `0x20000`. It assumes the internal hardware ROM boots the application directly without checking an OTA header or selecting between slots.

#### 2. OTA Scripts (Bootloader-Based)
  * **`eagle.app.v6.new.512.app1.ld` / `app2.ld`** : Purpose: 512 KB Flash using the "new" bootloader format. Split into two equal OTA partition slots (~236 KB max code size per app).
  * **`eagle.app.v6.new.1024.app1.ld` / `app2.ld`** : Purpose: 1 MB (and larger) Flash using the "new" bootloader format. Split into two ~492 KB OTA slots (`user1.bin` / `user2.bin`).
  * **`eagle.app.v6.new.2048.ld`**: Purpose: Single large application layout for 2 MB+ flash modules designed to work alongside special bootloaders or expanded static allocations.
  * **`eagle.app.v6.old.*.ld`**: Purpose: Legacy backward-compatibility layouts for projects targeted at very early Espressif bootloader releases.

#### 3. Core ROM Address Symbols
  * **`eagle.rom.addr.v6.ld`**: Purpose: Hardware ROM symbol map. Behavior: Does not define flash partitions. Instead, it provides the physical memory addresses of functions pre-baked into the ESP8266 internal hardware ROM (such as `axtls` crypto functions, low-level SPI functions, `printf`, and `malloc`). This file is included by other linker scripts.