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(@cindex @samp{--pcrel}): Rewrite option description.

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Nick Clifton 2000-08-01 16:57:01 +00:00
parent 666e11c5d4
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@ -1,3 +1,13 @@
2000-08-01 Nick Clifton <nickc@redhat.com>
* doc/c-m68k.texi (section M680x0 Options): Turn into a table
index by command line option.
2000-08-01 Michael Sokolov <msokolov@ivan.Harhan.ORG>
* doc/c-m68k.texi (@cindex @samp{--pcrel}): Rewrite option description.
(@node M68K-Branch): Rewrite to match the reality.
2000-07-31 Jason Eckhardt <jle@cygnus.com> 2000-07-31 Jason Eckhardt <jle@cygnus.com>
* doc/c-i860.texi: New file. * doc/c-i860.texi: New file.

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gas/doc/c-m68k.texi
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@ -27,9 +27,12 @@
@cindex options, M680x0 @cindex options, M680x0
@cindex M680x0 options @cindex M680x0 options
The Motorola 680x0 version of @code{@value{AS}} has a few machine The Motorola 680x0 version of @code{@value{AS}} has a few machine
dependent options. dependent options:
@table @samp
@cindex @samp{-l} option, M680x0 @cindex @samp{-l} option, M680x0
@item -l
You can use the @samp{-l} option to shorten the size of references to undefined You can use the @samp{-l} option to shorten the size of references to undefined
symbols. If you do not use the @samp{-l} option, references to undefined symbols. If you do not use the @samp{-l} option, references to undefined
symbols are wide enough for a full @code{long} (32 bits). (Since symbols are wide enough for a full @code{long} (32 bits). (Since
@ -41,6 +44,7 @@ This may be useful if you want the object file to be as small as possible, and
you know that the relevant symbols are always less than 17 bits away. you know that the relevant symbols are always less than 17 bits away.
@cindex @samp{--register-prefix-optional} option, M680x0 @cindex @samp{--register-prefix-optional} option, M680x0
@item --register-prefix-optional
For some configurations, especially those where the compiler normally For some configurations, especially those where the compiler normally
does not prepend an underscore to the names of user variables, the does not prepend an underscore to the names of user variables, the
assembler requires a @samp{%} before any use of a register name. This assembler requires a @samp{%} before any use of a register name. This
@ -54,6 +58,7 @@ refer to C variables and functions with the same names as register
names. names.
@cindex @samp{--bitwise-or} option, M680x0 @cindex @samp{--bitwise-or} option, M680x0
@item --bitwise-or
Normally the character @samp{|} is treated as a comment character, which Normally the character @samp{|} is treated as a comment character, which
means that it can not be used in expressions. The @samp{--bitwise-or} means that it can not be used in expressions. The @samp{--bitwise-or}
option turns @samp{|} into a normal character. In this mode, you must option turns @samp{|} into a normal character. In this mode, you must
@ -62,6 +67,7 @@ at the beginning of a line.
@cindex @samp{--base-size-default-16} @cindex @samp{--base-size-default-16}
@cindex @samp{--base-size-default-32} @cindex @samp{--base-size-default-32}
@item --base-size-default-16 --base-size-default-32
If you use an addressing mode with a base register without specifying If you use an addressing mode with a base register without specifying
the size, @code{@value{AS}} will normally use the full 32 bit value. the size, @code{@value{AS}} will normally use the full 32 bit value.
For example, the addressing mode @samp{%a0@@(%d0)} is equivalent to For example, the addressing mode @samp{%a0@@(%d0)} is equivalent to
@ -73,6 +79,7 @@ default behaviour.
@cindex @samp{--disp-size-default-16} @cindex @samp{--disp-size-default-16}
@cindex @samp{--disp-size-default-32} @cindex @samp{--disp-size-default-32}
@item --disp-size-default-16 --disp-size-default-32
If you use an addressing mode with a displacement, and the value of the If you use an addressing mode with a displacement, and the value of the
displacement is not known, @code{@value{AS}} will normally assume that displacement is not known, @code{@value{AS}} will normally assume that
the value is 32 bits. For example, if the symbol @samp{disp} has not the value is 32 bits. For example, if the symbol @samp{disp} has not
@ -85,15 +92,21 @@ to instead assume that the displacement is 16 bits. In this case,
@samp{--disp-size-default-32} option to restore the default behaviour. @samp{--disp-size-default-32} option to restore the default behaviour.
@cindex @samp{--pcrel} @cindex @samp{--pcrel}
Always generate PC relative branches. Actually what this option really @item --pcrel
does is to prevent PC relative branches from being turned into absolute Always keep branches PC-relative. In the M680x0 architecture all branches
jumps. If this cannot be done (because the specific architecture does are defined as PC-relative. However, on some processors they are limited
not have a suitable PC relative branch instruction), the assembler will to word displacements maximum. When @code{@value{AS}} needs a long branch
generate an error message. that is not available, it normally emits an absolute jump instead. This
option disables this substitution. When this option is given and no long
branches are available, only word branches will be emitted. An error
message will be generated if a word branch cannot reach its target. This
option has no effect on 68020 and other processors that have long branches.
@pxref{M68K-Branch,,Branch Improvement}.
@cindex @samp{-m68000} and related options @cindex @samp{-m68000} and related options
@cindex architecture options, M680x0 @cindex architecture options, M680x0
@cindex M680x0 architecture options @cindex M680x0 architecture options
@item -m68000
@code{@value{AS}} can assemble code for several different members of the @code{@value{AS}} can assemble code for several different members of the
Motorola 680x0 family. The default depends upon how @code{@value{AS}} Motorola 680x0 family. The default depends upon how @code{@value{AS}}
was configured when it was built; normally, the default is to assemble was configured when it was built; normally, the default is to assemble
@ -175,6 +188,7 @@ Do not assemble 68851 MMU instructions. This is the default for the
68000, 68010, and the CPU32. The 68040 accepts a somewhat different set 68000, 68010, and the CPU32. The 68040 accepts a somewhat different set
of MMU instructions. of MMU instructions.
@end table @end table
@end table
@node M68K-Syntax @node M68K-Syntax
@section Syntax @section Syntax
@ -410,28 +424,39 @@ cases that are more fully described after the table:
@smallexample @smallexample
Displacement Displacement
+------------------------------------------------- +------------------------------------------------------------
| 68020 68000/10 | 68020 68000/10, not PC-relative OK
Pseudo-Op |BYTE WORD LONG LONG non-PC relative Pseudo-Op |BYTE WORD LONG ABSOLUTE LONG JUMP **
+------------------------------------------------- +------------------------------------------------------------
jbsr |bsrs bsr bsrl jsr jsr jbsr |bsrs bsrw bsrl jsr
jra |bras bra bral jmp jmp jra |bras braw bral jmp
* jXX |bXXs bXX bXXl bNXs;jmpl bNXs;jmp * jXX |bXXs bXXw bXXl bNXs;jmp
* dbXX |dbXX dbXX dbXX; bra; jmpl * dbXX | N/A dbXXw dbXX;bras;bral dbXX;bras;jmp
* fjXX |fbXXw fbXXw fbXXl fbNXw;jmp fjXX | N/A fbXXw fbXXl N/A
XX: condition XX: condition
NX: negative of condition XX NX: negative of condition XX
@end smallexample @end smallexample
@center @code{*}---see full description below @center @code{*}---see full description below
@center @code{**}---this expansion mode is disallowed by @samp{--pcrel}
@table @code @table @code
@item jbsr @item jbsr
@itemx jra @itemx jra
These are the simplest jump pseudo-operations; they always map to one These are the simplest jump pseudo-operations; they always map to one
particular machine instruction, depending on the displacement to the particular machine instruction, depending on the displacement to the
branch target. branch target. This instruction will be a byte or word branch is that
is sufficient. Otherwise, a long branch will be emitted if available.
If no long branches are available and the @samp{--pcrel} option is not
given, an absolute long jump will be emitted instead. If no long
branches are available, the @samp{--pcrel} option is given, and a word
branch cannot reach the target, an error message is generated.
In addition to standard branch operands, @code{@value{AS}} allows these
pseudo-operations to have all operands that are allowed for jsr and jmp,
substituting these instructions if the operand given is not valid for a
branch instruction.
@item j@var{XX} @item j@var{XX}
Here, @samp{j@var{XX}} stands for an entire family of pseudo-operations, Here, @samp{j@var{XX}} stands for an entire family of pseudo-operations,
@ -442,10 +467,11 @@ list of pseudo-ops in this family is:
jvs jpl jmi jge jlt jgt jle jvs jpl jmi jge jlt jgt jle
@end smallexample @end smallexample
For the cases of non-PC relative displacements and long displacements on Usually, each of these pseudo-operations expands to a single branch
the 68000 or 68010, @code{@value{AS}} issues a longer code fragment in terms of instruction. However, if a word branch is not sufficient, no long branches
@var{NX}, the opposite condition to @var{XX}. For example, for the are available, and the @samp{--pcrel} option is not given, @code{@value{AS}}
non-PC relative case: issues a longer code fragment in terms of @var{NX}, the opposite condition
to @var{XX}. For example, under these conditions:
@smallexample @smallexample
j@var{XX} foo j@var{XX} foo
@end smallexample @end smallexample
@ -464,12 +490,24 @@ The full family of pseudo-operations covered here is
dbf dbra dbt dbf dbra dbt
@end smallexample @end smallexample
Other than for word and byte displacements, when the source reads Motorola @samp{db@var{XX}} instructions allow word displacements only. When
a word displacement is sufficient, each of these pseudo-operations expands
to the corresponding Motorola instruction. When a word displacement is not
sufficient and long branches are available, when the source reads
@samp{db@var{XX} foo}, @code{@value{AS}} emits @samp{db@var{XX} foo}, @code{@value{AS}} emits
@smallexample @smallexample
db@var{XX} oo1 db@var{XX} oo1
bra oo2 bras oo2
oo1:jmpl foo oo1:bral foo
oo2:
@end smallexample
If, however, long branches are not available and the @samp{--pcrel} option is
not given, @code{@value{AS}} emits
@smallexample
db@var{XX} oo1
bras oo2
oo1:jmp foo
oo2: oo2:
@end smallexample @end smallexample
@ -483,13 +521,9 @@ This family includes
fjugt fjule fjult fjun fjugt fjule fjult fjun
@end smallexample @end smallexample
For branch targets that are not PC relative, @code{@value{AS}} emits Each of these pseudo-operations always expands to a single Motorola
@smallexample coprocessor branch instruction, word or long. All Motorola coprocessor
fb@var{NX} oof branch instructions allow both word and long displacements.
jmp foo
oof:
@end smallexample
when it encounters @samp{fj@var{XX} foo}.
@end table @end table