Vram classes

Vram classes aim to help reduce duplicated data across the segments and more clearly organize the memory layout. This is not a common linker script concept. It was designed for the ease of use with complex memory layouts between multiple segments.

A vram class specifies a place in memory, which may be described in a somewhat complex way, so one or more segments can point to this class instead of try to describe the memory layout on the segment itself.

A vram class may describy a memory location by simply specifying a hardcoded vram (virtual RAM) location, the same address of an existing symbol or something more complex like the address of a vram class starts where one or more other vram classes ends (follow_classes).

A vram class is composed by two mandatory fields, the name field and exactly one of the fields that describe address memory locations. Specifying more than one or not specifying any of them is invalid.

Linker symbols for start, end and size are emitted for vram classes, similarly to how segments have linker symbols for their start, end and size. See linker_symbols_style.

The start symbol is defined depending on the given field that describe a memory location.
The end symbol is defined as equal to the end symbol of the largest segment that uses this vram class.
The size symbol is defined by the subtraction of the end and the start symbols.

Vram classes

`name`

This field is required.

The name of the corresponding vram class.

The name of a vram class must be unique between all the vram classes.

Example

vram_classes:
  - { name: battle_partner, fixed_vram: 0x80238000 }

Valid values

Non empty string.

`fixed_vram`

Forces the given vram class to be at a fixed vram address.

The start symbol for this vram classs will be hardcoded to the given value.

Example

vram_classes:
  - { name: segment_05, fixed_vram: 0x05000000 }

segments:
  - name: assets1
    vram_class: segment_05
    files:
      - { path: src/assets/assets1/texture.o }
      - { path: src/assets/assets1/dlist.o }

  - name: assets2
    vram_class: segment_05
    files:
      - { path: src/assets/assets2/texture.o }
      - { path: src/assets/assets2/dlist.o }

  - name: assets3
    vram_class: segment_05
    files:
      - { path: src/assets/assets3/texture.o }
      - { path: src/assets/assets3/dlist.o }

Valid values

Any unsigned integer.

`fixed_symbol`

Forces the given vram class to have the same address as the given symbol.

The start symbol for this vram classs will be hardcoded to the given symbol.

Example

vram_classes:
  - { name: battle_area2, fixed_symbol: Vine1Base }

segments:
  - name: omo2_1
    vram_class: battle_area2
    files:
      - { path: actor/shy_squad.o }

  - name: omo2_2
    vram_class: battle_area2
    files:
      - { path: actor/stilt_guy.o }

  - name: omo2_3
    vram_class: battle_area2
    files:
      - { path: actor/shy_stack.o }

Valid values

Non empty string.

`follow_classes`

A list of names of other vram classes.

Specifies that this vram class must follow the end of the largest vram class of the given list.

The start symbol for this vram classs will be equal to the largest end of the given vram classes.

Example

vram_classes:
  - { name: battle_partner, fixed_vram: 0x80238000 }
  - { name: battle_code, follows_classes: [battle_partner] }

  - { name: heaps2, fixed_vram: 0x80267FF0 }
  - { name: world_script_api, follows_classes: [heaps2] }

  - { name: texture_memory, follows_classes: [battle_partner, world_script_api] }

segments:
  - name: battle_partner_goompa
    vram_class: battle_partner
    files:
      - { path: src/battle_partner/goompa.o }
  - name: battle_partner_goombario
    vram_class: battle_partner
    files:
      - { path: src/battle_partner/goombario.o }

  - name: battle_code
    vram_class: battle_code
    files:
      - { path: src/battle_code/btl_states_actions.o }
      - { path: src/battle_code/camera.o }

  - name: heaps2
    vram_class: heaps2
    files:
      - { path: src/heaps2/heaps2.o }

  - name: world_script_api
    vram_class: world_script_api
    files:
      - { path: src/world/script_api/shops.o }
      - { path: src/world/script_api/rooms.o }

  - name: texture_memory
    vram_class: texture_memory
    files:
      - { path: src/texture_memory/texture_memory.o }

This example describes the following interactions between segments and vram classes:

The battle_partner_goompa and battle_partner_goombario segments will have the same vram address as the battle_partner vram class, which has a fixed vram address of 0x80238000.
battle_partner's end symbol will be set to the end symbol of either battle_partner_goompa or battle_partner_goombario. If the battle_partner_goompa segment is bigger then its end symbol will be used, otherwise the end symbol of battle_partner_goombario will be used.
The battle_code segment will have the same vram address as the battle_code vram class.
The vram address of the battle_code vram class will be the same as the end address of the battle_partner vram class (which is defined depending on the corresponding segments that use that vram class).
The heaps2 segment will have the same vram address as the heaps2 vram class which has a hardcoded address of 0x80267FF0.
The world_script_api segment will have the vram address of the world_script_api vram class, which its vram address is the same as the end address of the heaps2 vram class.
The texture_memory segment has the same vram as the texture_memory vram class. The vram address of the texture_memory vram class will be the same as the end symbol of the largest vram class between battle_partner and world_script_api.

TODO: Add images to explain this memory layout visually.

Valid values

A list of strings. The strings must be names of existing vram classes.

`keep_sections`

Wraps the file entries from the segments that reference this vram class with KEEP attributes.

KEEP is only relevant when link time garbage collection is enabled (the --gc-sections flag of GNU LD), since wrapping a section with a KEEP attribute tells the linker that this section should not be garbage collected, even if none of the symbols on that section is referenced by anything else that is actually used.

If link time garbage collection is enabled then it is recommended to set the entrypoint of this program by setting the slinky top-level attribute entry.

The keep_sections attribute allow specify if all the input sections (say .text, .data, etc) of a given file entry should be wrapped by KEEP or not. Alternatively a list of strings may be provided instead to specify which specific sections should be wrapped with KEEP, allowing for a more fine grained customization of this behavior.

Every segment referencing a vram class will inherit its keep_sections attribute, propagating this setting to all those segments and allowing the user to avoid unnecessary duplication. This setting may be overriden for specific segments that still want to reference the given vram class. See specifying a keep_sections attribute on the segments document for more information.

GNU LD documentation for KEEP.

Example

vram_classes:
  - { name: battle_partner, fixed_vram: 0x80238000, keep_sections: [.text] }
  - { name: segment_05, fixed_vram: 0x05000000, keep_sections: True }

segments:
  - name: battle_partner_goompa
    vram_class: battle_partner
    files:
      - { path: src/battle_partner/goompa.o }
  - name: battle_partner_goombario
    vram_class: battle_partner
    keep_sections: False
    files:
      - { path: src/battle_partner/goombario.o }

  - name: assets1
    vram_class: segment_05
    files:
      - { path: src/assets/texture.o }
      - { path: src/assets/dlist.o }

The above example defines two vram classes, battle_partner which defines keep_sections to keep only the .text section of the files of the segments that will reference thise vram class, and segment_05 which will keep every section of every segment referencing it.

The battle_partner_goompa segment references the battle_partner vram class and neither the segment itself or the files within the segment specify their own keep_sections, meaning all the .text sections of all the files of this segment will be wrapped with KEEPs.

On the other hand, the battle_partner_goombario segment (which references the battle_partner vram class too) sets its keep_sections attribute to False, meaning that no file of this segment should be wrapped with KEEPs, overriding the configuration of the battle_partner vram class for this specific segment.

Finally the assets1 segment will emit KEEPs for all the sections of every file on the segment since the segment_05 vram class did set True to the keep_sections attribute.

Valid values

Either a boolean or a list of sections (list of strings).

Default

False

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Vram classes

Table of contents

`name`

Example

Valid values

`fixed_vram`

Example

Valid values

`fixed_symbol`

Example

Valid values

`follow_classes`

Example

Valid values

`keep_sections`

Example

Valid values

Default

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Vram classes

Table of contents

name

Example

Valid values

fixed_vram

Example

Valid values

fixed_symbol

Example

Valid values

follow_classes

Example

Valid values

keep_sections

Example

Valid values

Default

`name`

`fixed_vram`

`fixed_symbol`

`follow_classes`

`keep_sections`