CodeModel

Generated code will assume the default for a particular target architecture.

Generated code will assume the default for JITed code on a particular target architecture.

The virtual address of code executed is known at link time. Additionally all symbols are known to be located in the virtual addresses in the range from 0 to 2^31 − 2^24 − 1 or from 0x00000000 to 0x7effffff.

This allows the compiler to encode symbolic references with offsets in the range from −(2^31) to 2^24 or from 0x80000000 to 0x01000000 directly in the sign extended immediate operands, with offsets in the range from 0 to 2^31 − 2^24 or from 0x00000000 to 0x7f000000 in the zero extended immediate operands and use instruction pointer relative addressing for the symbols with offsets in the range −(2^24) to 2^24 or 0xff000000 to 0x01000000.

This is the fastest code model and is suitable for the vast majority of programs.

The kernel of an operating system is usually rather small but runs in the negative half of the address space. So all symbols are defined to be in the range from 2^64 − 2^31 to 2^64 − 2^24 or from 0xffffffff80000000 to 0xffffffffff000000.

This code model has advantages similar to those of the small model, but allows encoding of zero extended symbolic references only for offsets from 2^31 to 2^31 + 2^24 or from 0x80000000 to 0x81000000. The range offsets for sign extended reference changes to 0 to 2^31 + 2^24 or 0x00000000 to 0x81000000.

In the medium model, the data section is split into two parts — the data section still limited in the same way as in the small code model and the large data section having no limits except for available addressing space. The program layout must be set in a way so that large data sections (.ldata, .lrodata, .lbss) come after the text and data sections.

This model requires the compiler to use movabs instructions to access large static data and to load addresses into registers, but keeps the advantages of the small code model for manipulation of addresses in the small data and text sections (specially needed for branches).

By default only data larger than 65535 bytes will be placed in the large data section.

The large code model makes no assumptions about addresses and sizes of sections.

The compiler is required to use the movabs instruction, as in the medium code model, even for dealing with addresses inside the text section. Additionally, indirect branches are needed when branching to addresses whose offset from the current instruction pointer is unknown.

It is possible to avoid the limitation on the text section in the small and medium models by breaking up the program into multiple shared libraries, so this model is strictly only required if the text of a single function becomes larger than what the medium model allows.

Returns the underlying LLVMCodeModel associated with this code model.