9.38.4 Assembler Directives
as for s390 supports all of the standard ELF
assembler directives as outlined in the main part of this document.
Some directives have been extended and there are some additional
directives, which are only available for the s390 as.
.insn- This directive permits the numeric representation of an instructions
and makes the assembler insert the operands according to one of the
instructions formats for ‘.insn’ (s390 Formats).
For example, the instruction ‘l %r1,24(%r15)’ could be written as
‘.insn rx,0x58000000,%r1,24(%r15)’.
.short.long.quad- This directive places one or more 16-bit (.short), 32-bit (.long), or
64-bit (.quad) values into the current section. If an ELF or TLS modifier
is used only the following expressions are allowed:
‘symbol@modifier + constant’,
‘symbol@modifier + label + constant’, and
‘symbol@modifier - label + constant’.
The following modifiers are available:
@got@got12- The @got modifier can be used for .short, .long and .quad. The @got12
modifier is synonym to @got. The symbol is added to the GOT. The symbol
term is replaced with offset from the start of the GOT to the GOT slot for
the symbol.
@gotoff- The @gotoff modifier can be used for .short, .long and .quad. 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 .long and .quad. A procedure linkage
table entry is generated for the symbol and a jump slot for the symbol
is added to the GOT. The symbol term is replaced with the offset from the
start of the GOT to the jump slot for the symbol.
@plt- The @plt modifier can be used for .long and .quad. A procedure linkage
table entry us generated for the symbol. The symbol term is replaced with
the address of the PLT entry for the symbol.
@pltoff- The @pltoff modifier can be used for .short, .long and .quad. The symbol
term is replaced with the offset from the start of the PLT to the address
of the symbol.
@tlsgd@tlsldm- The @tlsgd and @tlsldm modifier can be used for .long and .quad. A
tls_index structure for the symbol is added to the GOT. The symbol term is
replaced with the offset from the start of the GOT to the tls_index structure.
@gotntpoff@indntpoff- The @gotntpoff and @indntpoff modifier can be used for .long and .quad.
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. For @gotntpoff the
symbol term is replaced with the offset from the start of the GOT to the
GOT slot, for @indntpoff the symbol term is replaced with the address
of the GOT slot.
@dtpoff- The @dtpoff modifier can be used for .long and .quad. The symbol term
is replaced with the offset of the symbol relative to the start of the
TLS block it is contained in.
@ntpoff- The @ntpoff modifier can be used for .long and .quad. The symbol term
is replaced with the offset of the symbol relative to the TCB pointer.
For more information about the thread local storage modifiers see the
ELF extension documentation ‘ELF Handling For Thread-Local Storage’.
.ltorg- This directive causes the current contents of the literal pool to be
dumped to the current location (s390 Literal Pool Entries).
.machine STRING[+EXTENSION]...-
This directive allows changing the machine for which code is
generated.
string may be any of the -march=
selection options, or push, or pop. .machine
push saves the currently selected cpu, which may be restored with
.machine pop. Be aware that the cpu string has to be put
into double quotes in case it contains characters not appropriate
for identifiers. So you have to write "z9-109" instead of
just z9-109. Extensions can be specified after the cpu
name, separated by plus charaters. Valid extensions are:
htm,
nohtm,
vx,
novx.
They extend the basic instruction set with features from a higher
cpu level, or remove support for a feature from the given cpu
level.
Example: z13+nohtm allows all instructions of the z13 cpu
except instructions from the HTM facility.
.machinemode string- This directive allows to change the architecture mode for which code
is being generated.
string may be esa, zarch,
zarch_nohighgprs, push, or pop.
.machinemode zarch_nohighgprs can be used to prevent the
highgprs flag from being set in the ELF header of the output
file. This is useful in situations where the code is gated with a
runtime check which makes sure that the code is only executed on
kernels providing the highgprs feature.
.machinemode push saves the currently selected mode, which may
be restored with .machinemode pop.