Xtensa Options (Using the GNU Compiler Collection (GCC))

#### 3.20.59 Xtensa Options ¶

These options are supported for Xtensa targets:

`-mconst16` ¶
`-mno-const16`

  Enable or disable use of `CONST16` instructions for loading constant values. When enabled, `CONST16` instructions are always used in place of the standard `L32R` instructions. The use of `CONST16` is enabled by default only if the `L32R` instruction is not available.

`-mserialize-volatile` ¶
`-mno-serialize-volatile`

  When this option is enabled, GCC inserts `MEMW` instructions before `volatile` memory references to guarantee sequential consistency. The default is `-mserialize-volatile`. Use `-mno-serialize-volatile` to omit the `MEMW` instructions.

`-mforce-no-pic` ¶
`-mno-force-no-pic`

  For targets like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC), this option disables PIC for compiling kernel code.

`-mtext-section-literals` ¶
`-mno-text-section-literals`

  These options control the treatment of literal pools. The default is `-mno-text-section-literals`, which places literals in a separate section in the output file. This allows the literal pool to be placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With `-mtext-section-literals`, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files. Literals for each function are placed right before that function.

`-mauto-litpools` ¶
`-mno-auto-litpools`

  These options control the treatment of literal pools. The default is `-mno-auto-litpools`, which places literals in a separate section in the output file unless `-mtext-section-literals` is used. With `-mauto-litpools` the literals are interspersed in the text section by the assembler. Compiler does not produce explicit `.literal` directives and loads literals into registers with `MOVI` instructions instead of `L32R` to let the assembler do relaxation and place literals as necessary. This option allows assembler to create several literal pools per function and assemble very big functions, which may not be possible with `-mtext-section-literals`.

`-mtarget-align` ¶
`-mno-target-align`

  When this option is enabled, GCC instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening is performed. The default is `-mtarget-align`. These options do not affect the treatment of auto-aligned instructions like `LOOP`, which the assembler always aligns, either by widening density instructions or by inserting NOP instructions.

`-mlongcalls` ¶
`-mno-longcalls`

  When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct `CALL` instruction into an `L32R` followed by a `CALLX` instruction. The default is `-mno-longcalls`. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the assembler, not the compiler, so the assembly code generated by GCC still shows direct call instructions—look at the disassembled object code to see the actual instructions. Note that the assembler uses an indirect call for every cross-file call, not just those that really are out of range.

`-mabi=name` ¶

  Generate code for the specified ABI. Permissible values are: ‘`call0`’, ‘`windowed`’. Default ABI is chosen by the Xtensa core configuration.

`-mabi=call0` ¶

  When this option is enabled function parameters are passed in registers `a2` through `a7`, registers `a12` through `a15` are caller-saved, and register `a15` may be used as a frame pointer. When this version of the ABI is enabled the C preprocessor symbol `__XTENSA_CALL0_ABI__` is defined.

`-mabi=windowed` ¶

  When this option is enabled function parameters are passed in registers `a10` through `a15`, and called function rotates register window by 8 registers on entry so that its arguments are found in registers `a2` through `a7`. Register `a7` may be used as a frame pointer. Register window is rotated 8 registers back upon return. When this version of the ABI is enabled the C preprocessor symbol `__XTENSA_WINDOWED_ABI__` is defined.

`-mextra-l32r-costs=n` ¶

  Specify an extra cost of instruction RAM/ROM access for `L32R` instructions, in clock cycles. This affects, when optimizing for speed, whether loading a constant from literal pool using `L32R` or synthesizing the constant from a small one with a couple of arithmetic instructions. The default value is 0.

`-mstrict-align` ¶
`-mno-strict-align`

  Avoid or allow generating memory accesses that may not be aligned on a natural object boundary as described in the architecture specification. The default is `-mno-strict-align` for cores that support both unaligned loads and stores in hardware and `-mstrict-align` for all other cores.