-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
as generates code
for any instruction or feature that is supported by some version of the
960 (even if this means mixing architectures!). In principle,
as attempts to deduce the minimal sufficient processor type if
none is specified; depending on the object code format, the processor type may
be recorded in the object file. If it is critical that the as
output match a specific architecture, specify that architecture explicitly.
-b
call increment routine
.word 0 # pre-counter
Label: BR
call increment routine
.word 0 # post-counter
The counter following a branch records the number of times that branch
was not taken; the differenc between the two counters is the
number of times the branch was taken.
A table of every such Label is also generated, so that the
external postprocessor gbr960 (supplied by Intel) can locate all
the counters. This table is always labelled `__BRANCH_TABLE__';
this is a local symbol to permit collecting statistics for many separate
object files. The table is word aligned, and begins with a two-word
header. The first word, initialized to 0, is used in maintaining linked
lists of branch tables. The second word is a count of the number of
entries in the table, which follow immediately: each is a word, pointing
to one of the labels illustrated above.
The first word of the header is used to locate multiple branch tables,
since each object file may contain one. Normally the links are
maintained with a call to an initialization routine, placed at the
beginning of each function in the file. The GNU C compiler
generates these calls automatically when you give it a `-b' option.
For further details, see the documentation of `gbr960'.
-no-relax
as should generate errors instead, if the target displacement
is larger than 13 bits.
This option does not affect the Compare-and-Jump instructions; the code
emitted for them is always adjusted when necessary (depending on
displacement size), regardless of whether you use `-no-relax'.
as generates IEEE floating-point numbers for the directives
`.float', `.double', `.extended', and `.single'.
.bss symbol, length, align
.lcomm symbol , length.
.extended flonums
.extended expects zero or more flonums, separated by commas; for
each flonum, `.extended' emits an IEEE extended-format (80-bit)
floating-point number.
.leafproc call-lab, bal-lab
callj instruction to enable faster calls of leaf
procedures. If a procedure is known to call no other procedures, you
may define an entry point that skips procedure prolog code (and that does
not depend on system-supplied saved context), and declare it as the
bal-lab using `.leafproc'. If the procedure also has an
entry point that goes through the normal prolog, you can specify that
entry point as call-lab.
A `.leafproc' declaration is meant for use in conjunction with the
optimized call instruction `callj'; the directive records the data
needed later to choose between converting the `callj' into a
bal or a call.
call-lab is optional; if only one argument is present, or if the
two arguments are identical, the single argument is assumed to be the
bal entry point.
.sysproc name, index
All Intel 960 machine instructions are supported; see section i960 Command-line Options for a discussion of selecting the instruction subset for a particular 960 architecture.
Some opcodes are processed beyond simply emitting a single corresponding instruction: `callj', and Compare-and-Branch or Compare-and-Jump instructions with target displacements larger than 13 bits.
callj
You can write callj to have the assembler or the linker determine
the most appropriate form of subroutine call: `call',
`bal', or `calls'. If the assembly source contains
enough information--a `.leafproc' or `.sysproc' directive
defining the operand--then as translates the
callj; if not, it simply emits the callj, leaving it
for the linker to resolve.
The 960 architectures provide combined Compare-and-Branch instructions that permit you to store the branch target in the lower 13 bits of the instruction word itself. However, if you specify a branch target far enough away that its address won't fit in 13 bits, the assembler can either issue an error, or convert your Compare-and-Branch instruction into separate instructions to do the compare and the branch.
Whether as gives an error or expands the instruction depends
on two choices you can make: whether you use the `-no-relax' option,
and whether you use a "Compare and Branch" instruction or a "Compare
and Jump" instruction. The "Jump" instructions are always
expanded if necessary; the "Branch" instructions are expanded when
necessary unless you specify -no-relax---in which case
as gives an error instead.
These are the Compare-and-Branch instructions, their "Jump" variants, and the instruction pairs they may expand into:
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