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Docs: add speed and size build flags to package.mk readme #3839

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Docs: add speed and size build flags to package.mk readme #3839

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24 changes: 13 additions & 11 deletions packages/readme.md
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Expand Up @@ -114,15 +114,17 @@ Build flags implement often used build options. Normally these are activated be

Set the variable `PKG_BUILD_FLAGS` in the `package.mk` to enable/disable the single flags. It is a space separated list. The flags can enabled with a `+` prefix, and disabled with a `-`.

| flag | default | affected stage | description |
|----------|----------|----------------|-------------|
| pic | disabled | target/init | [Position Independent Code](https://en.wikipedia.org/wiki/Position-independent_code) |
| pic:host | disabled | host/bootstrap | see above |
| lto | disabled | target/init | enable LTO (Link Time optimization) in the compiler and linker unless disabled via `LTO_SUPPORT`. Compiles non-fat LTO objects (only bytecode) and performs single-threaded optimization at link stage |
| lto-parallel | disabled | target/init | same as `lto` but enable parallel optimization at link stage. Only enable this if the package build doesn't run multiple linkers in parallel otherwise this can result in lots of parallel processes! |
| lto-fat | disabled | target/init | same as `lto` but compile fat LTO objects (bytecode plus optimized assembly). This increases compile time but can be useful to create static libraries suitable both for LTO and non-LTO linking |
| lto-off | disabled | target/init | explicitly disable LTO in the compiler and linker |
| gold | depend on `GOLD_SUPPORT` | target/init | can only disabled, use of the GOLD-Linker |
| flag | default | affected stage(s) | description |
|----------|----------|-------------------|-------------|
| pic | disabled | target, init | [Position Independent Code](https://en.wikipedia.org/wiki/Position-independent_code) |
| pic:host | disabled | host, bootstrap | see above |
| speed | disabled | target, init | replaces default `-O2` compiler optimization with `-O3` (can only enable; overrules size) |
| size | disabled | target, init | replaces default `-O2` compiler optimization with `-Os` (can only enable) |
| lto | disabled | target, init | enable LTO (Link Time optimization) in the compiler and linker unless disabled via `LTO_SUPPORT`. Compiles non-fat LTO objects (only bytecode) and performs single-threaded optimization at link stage |
| lto-parallel | disabled | target, init | same as `lto` but enables parallel optimization at link stage. Only enable this if the package build doesn't run multiple linkers in parallel otherwise this can result in lots of parallel processes! |
| lto-fat | disabled | target, init | same as `lto` but compile fat LTO objects (bytecode plus optimized assembly). This increases compile time but can be useful to create static libraries suitable both for LTO and non-LTO linking |
| lto-off | disabled | target, init | explicitly disable LTO in the compiler and linker |
| gold | enabled by `GOLD_SUPPORT` | target, init | do not use GOLD-Llinker (can only disable) |
| parallel | enabled | all | `make` or `ninja` builds with multiple threads/processes (or not) |
| strip | enabled | target | strips executables (or not) |

Expand All @@ -133,8 +135,8 @@ PKG_BUILD_FLAGS="-parallel"
```

## Functions
All build steps in the LibreELEC build system, a done by shell function.
These functions can overwritten in the `package.mk`. But this raises problems, when the build system is updated. To reduce the problem, most function was extended by `pre_` and `post_` scripts, to use instead.
All build steps in the LibreELEC build system are done by shell function.
These functions can be overwritten in the `package.mk`. However, this raises problems when the build system is updated. To reduce the impact, most functions are extended by `pre_` and `post_` scripts to use instead.

When it is nesseary to replace configure, make and makeinstall, please use `PKG_TOOLCHAIN="manual"`.

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