tls_model

The tracking issue for this feature is: None.

Option -Z tls-model controls TLS model used to generate code for accessing #[thread_local] static items.

Supported values for this option are:

• global-dynamic - General Dynamic TLS Model (alternatively called Global Dynamic) is the most general option usable in all circumstances, even if the TLS data is defined in a shared library loaded at runtime and is accessed from code outside of that library. This is the default for most targets.
• local-dynamic - model usable if the TLS data is only accessed from the shared library or executable it is defined in. The TLS data may be in a library loaded after startup (via dlopen).
• initial-exec - model usable if the TLS data is defined in the executable or in a shared library loaded at program startup. The TLS data must not be in a library loaded after startup (via dlopen).
• local-exec - model usable only if the TLS data is defined directly in the executable, but not in a shared library, and is accessed only from that executable.
• emulated - Uses thread-specific data keys to implement emulated TLS. It is like using a general-dynamic TLS model for all modes.

rustc and LLVM may use a more optimized model than specified if they know that we are producing an executable rather than a library, or that the static item is private enough.