9.38.2 RISC-V Directives

The following table lists all available RISC-V specific directives.

.align size-log-2

Align to the given boundary, with the size given as log2 the number of bytes to align to.

.half value

.word value

.dword value

Emits a half-word, word, or double-word value at the current position.

.dtprelword value

.dtpreldword value

Emits a DTP-relative word (or double-word) at the current position. This is meant to be used by the compiler in shared libraries for DWARF debug info for thread local variables.

.bss

Sets the current section to the BSS section.

.uleb128 value

.sleb128 value

Emits a signed or unsigned LEB128 value at the current position. This only accepts constant expressions, because symbol addresses can change with relaxation, and we don't support relocations to modify LEB128 values at link time.

.option argument

Modifies RISC-V specific assembler options inline with the assembly code. This is used when particular instruction sequences must be assembled with a specific set of options. For example, since we relax addressing sequences to shorter GP-relative sequences when possible the initial load of GP must not be relaxed and should be emitted as something like

          	.option push
          	.option norelax
          	la gp, __global_pointer$
          	.option pop

in order to produce after linker relaxation the expected

          	auipc gp, %pcrel_hi(__global_pointer$)
          	addi gp, gp, %pcrel_lo(__global_pointer$)

instead of just

          	addi gp, gp, 0

It's not expected that options are changed in this manner during regular use, but there are a handful of esoteric cases like the one above where users need to disable particular features of the assembler for particular code sequences. The complete list of option arguments is shown below:

push

pop

Pushes or pops the current option stack. These should be used whenever changing an option in line with assembly code in order to ensure the user's command-line options are respected for the bulk of the file being assembled.

rvc

norvc

Enables or disables the generation of compressed instructions. Instructions are opportunistically compressed by the RISC-V assembler when possible, but sometimes this behavior is not desirable.

pic

nopic

Enables or disables position-independent code generation. Unless you really know what you're doing, this should only be at the top of a file.

relax

norelax

Enables or disables relaxation. The RISC-V assembler and linker opportunistically relax some code sequences, but sometimes this behavior is not desirable.

.insn value

.insn value

This directive permits the numeric representation of an instructions and makes the assembler insert the operands according to one of the instruction formats for ‘.insn’ (RISC-V-Formats). For example, the instruction ‘add a0, a1, a2’ could be written as ‘.insn r 0x33, 0, 0, a0, a1, a2’.

.attribute tag, value

Set the object attribute tag to value.

The tag is either an attribute number, or one of the following: Tag_RISCV_arch, Tag_RISCV_stack_align, Tag_RISCV_unaligned_access, Tag_RISCV_priv_spec, Tag_RISCV_priv_spec_minor, Tag_RISCV_priv_spec_revision.