Next: M68K-Chars, Up: M68K-opcodes
Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instruction that reach the target. Generally these mnemonics are made by substituting `j' for `b' at the start of a Motorola mnemonic.
The following table summarizes the pseudo-operations. A * flags
cases that are more fully described after the table:
Displacement
+------------------------------------------------------------
| 68020 68000/10, not PC-relative OK
Pseudo-Op |BYTE WORD LONG ABSOLUTE LONG JUMP **
+------------------------------------------------------------
jbsr |bsrs bsrw bsrl jsr
jra |bras braw bral jmp
* jXX |bXXs bXXw bXXl bNXs;jmp
* dbXX | N/A dbXXw dbXX;bras;bral dbXX;bras;jmp
fjXX | N/A fbXXw fbXXl N/A
XX: condition
NX: negative of condition XX
*—see full description below**—this expansion mode is disallowed by `--pcrel'jbsrjraIn addition to standard branch operands, 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.
jXX jhi jls jcc jcs jne jeq jvc
jvs jpl jmi jge jlt jgt jle
Usually, each of these pseudo-operations expands to a single branch
instruction. However, if a word branch is not sufficient, no long branches
are available, and the `--pcrel' option is not given, as
issues a longer code fragment in terms of NX, the opposite condition
to XX. For example, under these conditions:
jXX foo
gives
bNXs oof
jmp foo
oof:
dbXX dbhi dbls dbcc dbcs dbne dbeq dbvc
dbvs dbpl dbmi dbge dblt dbgt dble
dbf dbra dbt
Motorola `dbXX' 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
`dbXX foo', as emits
dbXX oo1
bras oo2
oo1:bral foo
oo2:
If, however, long branches are not available and the `--pcrel' option is
not given, as emits
dbXX oo1
bras oo2
oo1:jmp foo
oo2:
fjXX fjne fjeq fjge fjlt fjgt fjle fjf
fjt fjgl fjgle fjnge fjngl fjngle fjngt
fjnle fjnlt fjoge fjogl fjogt fjole fjolt
fjor fjseq fjsf fjsne fjst fjueq fjuge
fjugt fjule fjult fjun
Each of these pseudo-operations always expands to a single Motorola coprocessor branch instruction, word or long. All Motorola coprocessor branch instructions allow both word and long displacements.