s390: Improve coding of .insn pseudo-mnemonics without operands
Allows omitting the trailing comma in .insn pseudo-mnemonics when all operands are optional, improving syntax for s390 assembly.
This patch enhances the s390 assembler’s handling of the .insn pseudo-mnemonic by allowing the omission of the trailing comma when all operands are optional and none are provided. Previously, a trailing comma was required even when no operands were specified (e.g., .insn INSN-FMT,OPCODE,). The change simplifies the syntax to .insn INSN-FMT,OPCODE, making it more natural and aligning with future changes to make all operands optional for rre and s mnemonics. It also generalizes the logic for handling .insn mnemonics with no operands.
In Details
This patch modifies gas/config/tc-s390.c to relax the syntax requirement for s390 .insn pseudo-mnemonics. Specifically, it allows omitting the comma that traditionally follows the opcode constant when all operands are optional and absent. This change, located within the s390_insn function, simplifies the syntax for certain s390 instructions, such as rre and s, by removing the need for a trailing comma (e.g., .insn RRE,0x, becomes .insn RRE,0x). This is a prerequisite for fully optional operands in these mnemonics, aligning with the architecture specification.
- .insn
- An assembler pseudo-mnemonic that allows embedding raw machine instructions using their format and opcode.
- pseudo-mnemonic
- An assembler directive that represents a machine instruction or a sequence of instructions using a symbolic name.
- s390
- IBM's mainframe and enterprise server architecture.
- optional operands
- Operands for an instruction or pseudo-mnemonic that are not required and can be omitted, often controlled by the instruction format or specific flags.