3.17.36 Xtensa Options
The Xtensa architecture is designed to support many different
configurations. The compiler's default options can be set to match a
particular Xtensa configuration by copying a configuration file into the
GCC sources when building GCC. The options below may be used to
override the default options.
- Specify big-endian or little-endian byte ordering for the target Xtensa
- Enable or disable use of the optional Xtensa code density instructions.
- Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
will generate MAC16 instructions from standard C code, with the
limitation that it will use neither the MR register file nor any
instruction that operates on the MR registers. When this option is
disabled, GCC will translate 16-bit multiply/accumulate operations to a
combination of core instructions and library calls, depending on whether
any other multiplier options are enabled.
- Enable or disable use of the 16-bit integer multiplier option. When
enabled, the compiler will generate 16-bit multiply instructions for
multiplications of 16 bits or smaller in standard C code. When this
option is disabled, the compiler will either use 32-bit multiply or
MAC16 instructions if they are available or generate library calls to
perform the multiply operations using shifts and adds.
- Enable or disable use of the 32-bit integer multiplier option. When
enabled, the compiler will generate 32-bit multiply instructions for
multiplications of 32 bits or smaller in standard C code. When this
option is disabled, the compiler will generate library calls to perform
the multiply operations using either shifts and adds or 16-bit multiply
instructions if they are available.
- Enable or disable use of the optional normalization shift amount
NSA) instructions to implement the built-in
- Enable or disable use of the optional minimum and maximum value
- Enable or disable use of the optional sign extend (
- Enable or disable support for the boolean register file used by Xtensa
coprocessors. This is not typically useful by itself but may be
required for other options that make use of the boolean registers (e.g.,
the floating-point option).
- Enable or disable use of the floating-point option. When enabled, GCC
generates floating-point instructions for 32-bit
operations. When this option is disabled, GCC generates library calls
to emulate 32-bit floating-point operations using integer instructions.
Regardless of this option, 64-bit
double operations are always
emulated with calls to library functions.
- Enable or disable use of fused multiply/add and multiply/subtract
instructions in the floating-point option. This has no effect if the
floating-point option is not also enabled. Disabling fused multiply/add
and multiply/subtract instructions forces the compiler to use separate
instructions for the multiply and add/subtract operations. This may be
desirable in some cases where strict IEEE 754-compliant results are
required: the fused multiply add/subtract instructions do not round the
intermediate result, thereby producing results with more bits of
precision than specified by the IEEE standard. Disabling fused multiply
add/subtract instructions also ensures that the program output is not
sensitive to the compiler's ability to combine multiply and add/subtract
- 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
- 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
- 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 will be performed. The
default is -mtarget-align. These options do not affect the
treatment of auto-aligned instructions like
LOOP, which the
assembler will always align, either by widening density instructions or
by inserting no-op instructions.
- 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
instruction into an
L32R followed by a
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 will still show direct call
instructions—look at the disassembled object code to see the actual
instructions. Note that the assembler will use an indirect call for
every cross-file call, not just those that really will be out of range.