huntedbytheirsandSisyphus
060fc03ab7
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <[email protected]>
76 lines
3.4 KiB
Markdown
76 lines
3.4 KiB
Markdown
# Compatibility
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vlibc offers five compatibility profiles, selected at configure time. They are
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mutually exclusive; the default is `vlibc`.
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| Level | Flag | Profile | What it provides |
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|-------|----------------------|-------------|---------------------------------------------------------|
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| 1 | `--enable-onlyposix` | `onlyposix` | Pure POSIX, nothing more — the lightest possible build. |
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| 2 | `--enable-muslmimic` | `muslmimic` | musl-like, still light, with musl-compatible features. |
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| 3 | `--enable-muslext` | `muslext` | An extension of musl, adding more. |
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| 4 | `--enable-spoof` | `spoof` | A glibc replica: emulates glibc for drop-in compatibility, higher than `muslext` or `vlibc` full. |
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| 5 | *(default)* | `vlibc` | glibc-extended: glibc minus its baggage, plus extended standard features. High (but not spoof-level) glibc compatibility. |
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## Profile mechanism
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The profiles map onto a single integer level, `VLIBC_LEVEL`. Levels are
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**cumulative**: a profile at level N exposes everything whose minimum level is
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`<= N`.
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| Level | Classification |
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|-------|-----------------------------------------|
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| 1 | ISO C + POSIX base |
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| 2 | + BSD / XSI extensions |
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| 3 | + GNU extensions |
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Public headers gate declarations with `#if VLIBC_LEVEL >= N`; a function whose
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minimum level is 2 is only declared when the active profile is level 2 or
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higher. The build applies the same rule to sources via
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`AM_CONDITIONAL([PROFILE_GE_2])` and `AM_CONDITIONAL([PROFILE_GE_3])`, so each
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level's implementation files are only compiled when the selected profile
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reaches that level.
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The generated installed header `include/vlibc/features.h` exposes the macros
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the gating is based on:
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- `VLIBC_LEVEL` — the active profile's integer level.
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- `VLIBC_PROFILE` — the selected profile name.
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- `VLIBC_LEVEL_GE(n)` — expands to 1 when `VLIBC_LEVEL >= n`, 0 otherwise.
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### Slice manifest
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The initial implementation covers eight string/memory functions, classified as
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follows:
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| Function | Level | Origin |
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|--------------|-------|---------|
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| `memcpy` | L1 | ISO C |
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| `memmove` | L1 | ISO C |
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| `memset` | L1 | ISO C |
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| `strlen` | L1 | ISO C |
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| `strcmp` | L1 | ISO C |
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| `strlcpy` | L2 | BSD |
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| `strlcat` | L2 | BSD |
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| `strcasestr` | L3 | GNU |
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Profiles 4 and 5 (`spoof`, `vlibc`) build on the same level mechanism but are
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not implemented in this increment beyond their configure declarations.
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## Differences from glibc
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- **No legacy baggage.** vlibc targets modern, standard-conforming behavior and
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drops glibc's deprecated and non-standard behaviors unless a profile
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explicitly restores them.
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- **Extended standard features.** The `vlibc` profile adds extensions on top of
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the C and POSIX standards that glibc does not provide.
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- **Spoofing is opt-in.** The `--enable-spoof` profile re-enables the
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long-standing legacy behaviors that scripts rely on, for drop-in
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compatibility with existing binaries and build systems.
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## Full static linking
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Every profile except `spoof` must be able to link fully statically. The
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`spoof` profile is exempt: its glibc-emulation layer depends on dynamic
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facilities (e.g. `dlopen`-based compatibility shims) that a static build cannot
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provide.
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