Symbols in position-independent code

When generating position-independent code (SVR4 PIC) for use in cris-axis-linux-gnu or crisv32-axis-linux-gnu shared libraries, symbol suffixes are used to specify what kind of run-time symbol lookup will be used, expressed in the object as different relocation types . Usually, all absolute symbol values must be located in a table, the global offset table , leaving the code position-independent; independent of values of global symbols and independent of the address of the code. The suffix modifies the value of the symbol, into for example an index into the global offset table where the real symbol value is entered, or a PC-relative value, or a value relative to the start of the global offset table. All symbol suffixes start with the character ‘ : ’ (omitted in the list below). Every symbol use in code or a read-only section must therefore have a PIC suffix to enable a useful shared library to be created. Usually, these constructs must not be used with an additive constant offset as is usually allowed, i.e. no 4 as in symbol + 4 is allowed. This restriction is checked at link-time, not at assembly-time.

Attaching this suffix to a symbol in an instruction causes the symbol to be entered into the global offset table. The value is a 32-bit index for that symbol into the global offset table. The name of the corresponding relocation is ‘ R_CRIS_32_GOT ’. Example: move.d [$r0+extsym:GOT],$r9
Same as for ‘ GOT ’, but the value is a 16-bit index into the global offset table. The corresponding relocation is ‘ R_CRIS_16_GOT ’. Example: move.d [$r0+asymbol:GOT16],$r10
This suffix is used for function symbols. It causes a procedure linkage table , an array of code stubs, to be created at the time the shared object is created or linked against, together with a global offset table entry. The value is a pc-relative offset to the corresponding stub code in the procedure linkage table. This arrangement causes the run-time symbol resolver to be called to look up and set the value of the symbol the first time the function is called (at latest; depending environment variables). It is only safe to leave the symbol unresolved this way if all references are function calls. The name of the relocation is ‘ R_CRIS_32_PLT_PCREL ’. Example: add.d fnname:PLT,$pc
Like PLT, but the value is relative to the beginning of the global offset table. The relocation is ‘ R_CRIS_32_PLT_GOTREL ’. Example: move.d fnname:PLTG,$r3
Similar to ‘ PLT ’, but the value of the symbol is a 32-bit index into the global offset table. This is somewhat of a mix between the effect of the ‘ GOT ’ and the ‘ PLT ’ suffix; the difference to ‘ GOT ’ is that there will be a procedure linkage table entry created, and that the symbol is assumed to be a function entry and will be resolved by the run-time resolver as with ‘ PLT ’. The relocation is ‘ R_CRIS_32_GOTPLT ’. Example: jsr [$r0+fnname:GOTPLT]
A variant of ‘ GOTPLT ’ giving a 16-bit value. Its relocation name is ‘ R_CRIS_16_GOTPLT ’. Example: jsr [$r0+fnname:GOTPLT16]
This suffix must only be attached to a local symbol, but may be used in an expression adding an offset. The value is the address of the symbol relative to the start of the global offset table. The relocation name is ‘ R_CRIS_32_GOTREL ’. Example: move.d [$r0+localsym:GOTOFF],r3