s390 Operand Modifier - Using as
Description: Using as

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##### 9.32.3.6 Instruction Operand Modifier

If a symbol modifier is attached to a symbol in an expression for an instruction operand field, the symbol term is replaced with a reference to an object in the global offset table (GOT) or the procedure linkage table (PLT). The following expressions are allowed: ‘`symbol@modifier + constant`’, ‘`symbol@modifier + label + constant`’, and ‘`symbol@modifier - label + constant`’. The term ‘`symbol`’ is the symbol that will be entered into the GOT or PLT, ‘`label`’ is a local label, and ‘`constant`’ is an arbitrary expression that the assembler can evaluate to a constant value.

The term ‘`(symbol + constant1)@modifier +/- label + constant2`’ is also accepted but a warning message is printed and the term is converted to ‘`symbol@modifier +/- label + constant1 + constant2`’.

`@got`
`@got12`
  The @got modifier can be used for displacement fields, 16-bit immediate fields and 32-bit pc-relative immediate fields. The @got12 modifier is synonym to @got. The symbol is added to the GOT. For displacement fields and 16-bit immediate fields the symbol term is replaced with the offset from the start of the GOT to the GOT slot for the symbol. For a 32-bit pc-relative field the pc-relative offset to the GOT slot from the current instruction address is used.
`@gotent`
  The @gotent modifier can be used for 32-bit pc-relative immediate fields. The symbol is added to the GOT and the symbol term is replaced with the pc-relative offset from the current instruction to the GOT slot for the symbol.
`@gotoff`
  The @gotoff modifier can be used for 16-bit immediate fields. The symbol term is replaced with the offset from the start of the GOT to the address of the symbol.
`@gotplt`
  The @gotplt modifier can be used for displacement fields, 16-bit immediate fields, and 32-bit pc-relative immediate fields. A procedure linkage table entry is generated for the symbol and a jump slot for the symbol is added to the GOT. For displacement fields and 16-bit immediate fields the symbol term is replaced with the offset from the start of the GOT to the jump slot for the symbol. For a 32-bit pc-relative field the pc-relative offset to the jump slot from the current instruction address is used.
`@plt`
  The @plt modifier can be used for 16-bit and 32-bit pc-relative immediate fields. A procedure linkage table entry is generated for the symbol. The symbol term is replaced with the relative offset from the current instruction to the PLT entry for the symbol.
`@pltoff`
  The @pltoff modifier can be used for 16-bit immediate fields. The symbol term is replaced with the offset from the start of the PLT to the address of the symbol.
`@gotntpoff`
  The @gotntpoff modifier can be used for displacement fields. The symbol is added to the static TLS block and the negated offset to the symbol in the static TLS block is added to the GOT. The symbol term is replaced with the offset to the GOT slot from the start of the GOT.
`@indntpoff`
  The @indntpoff modifier can be used for 32-bit pc-relative immediate fields. The symbol is added to the static TLS block and the negated offset to the symbol in the static TLS block is added to the GOT. The symbol term is replaced with the pc-relative offset to the GOT slot from the current instruction address.

For more information about the thread local storage modifiers ‘`gotntpoff`’ and ‘`indntpoff`’ see the ELF extension documentation ‘`ELF Handling For Thread-Local Storage`’.