Assembly language programs can be assembled with the as command or the cc command. The ld command or the cc command can be used to link assembled programs. This section discusses the following:
The as command invokes the assembler. The syntax for the as command is:
as [ -a Mode ] [ -o ObjectFile ] [ -n Name ] [ -u ] [ -l [ ListFile ] ] [ -W | -w ] [ -x [ XCrossFile ] ] [ -s [ ListFile ] ] [ -m ModeName ] [ File ]
The as command reads and assembles the file specified by the File parameter. By convention, this file has a suffix of .s. If no file is specified, the as command reads and assembles standard input. By default, the as command stores its output in a file named a.out. The output is stored in the XCOFF file format.
All flags for the as command are optional.
The ld command is used to link object files. See the ld command for more information.
The assembler respects the setting of the OBJECT_MODE environment variable. If neither -a32 or -a64 is used, the environment is examined for this variable. If the value of the variable is anything other than the values listed in the following table, an error message is generated and the assembler exits with a non-zero return code. The implied behavior corresponding to the valid settings are as follows:
|OBJECT_MODE=32||Produce 32-bit object code. The default machine setting is com.|
|OBJECT_MODE=64||Produce 64-bit object code (XCOFF64 files). The default machine setting is ppc64.|
The following flags are recognized by the as command:
|-a Mode||Specifies the mode in which the as command operates. By default, the as command operates in 32-bit mode, but the mode can be explicitly set by using the flag -a32 for 32-bit mode operation or -a64 for 64-bit mode operation.|
|-o ObjectFile||Writes the output of the assembly process to the specified file instead of to the a.out file.|
|-n Name||Specifies the name that appears in the header of the assembler listing. By default, the header contains the name of the assembler source file.|
|-l[ListFile]|| Produces an assembler listing. If you do not specify a file
name, a default name is produced by replacing the suffix
extension of the source file name with a .lst extension.
(By convention, the source file suffix is a .s.) For
If the source code is from standard input and the -l flag is used without specifying an assembler-listing file name, the listing file name is a.lst.
|-s[ListFile]|| Indicates whether or not a mnemonics cross-reference for
POWER and PowerPC is included in the assembler
listing. If this flag is omitted, no mnemonics cross-reference
is produced. If this flag is used, the assembler listing will
have POWER mnemonics if the source contains
PowerPC mnemonics, and will have PowerPC
mnemonics if the source contains POWER mnemonics.
The mnemonics cross-reference is restricted to instructions that have different mnemonics in POWER and PowerPC, but that have the same op code, function, and input operand format.
Because the -s flag is used to change the assembler-listing format, it implies the -l flag. If both option flags are used and different assembler-listing file names (specified by the ListFile variable) are given, the listing file name specified by the ListFile variable used with the -l flag is used. If an assembler-listing file name is not specified with either the -l or -s flag, a default assembler listing file name is produced by replacing the suffix extension of the source file name with a .lst extension.
|-u||Accepts an undefined symbol as an extern so that an error message is not displayed. Otherwise, undefined symbols are flagged with error messages.|
|-W||Turns off all warning message reporting, including the instructional warning messages (the POWER and PowerPC incompatibility warnings).|
|-w||Turns on warning message reporting, including reporting of instructional warning messages (the POWER and PowerPC incompatibility warnings).|
Note: When neither -W nor -w is specified, the instructional warnings are reported, but other warnings are suppressed.
|-x[XCrossFile]|| Produces cross-reference output. If you do not specify a
file name, a default name is produced by replacing the
suffix extension of the source file name with an .xref
extension. By convention, the suffix is a .s. For
Note: The assembler does not generate an object file when the -x flag is used.
|-m ModeName|| Indicates the assembly mode. This flag has lower priority
than the .machine pseudo-op.
If this flag is not used and no .machine pseudo-op is present in the source program, the default assembly mode is used. The default assembly mode has the POWER/PowerPC intersection as the target environment, but treats all POWER/PowerPC incompatibility errors (including instructions outside the POWER/PowerPC intersection and invalid form errors) as instructional warnings.
If an assembly mode that is not valid is specified and no .machine pseudo-op is present in the source program, an error is reported and the default assembly mode is used for instruction validation in pass 1 of the assembler.
If the -m flag is used, the ModeName variable can specify one of the following values:
|File||Specifies the source file. If no file is specified, the source code is taken from standard input.|
The cc command can be used to assemble and link an assembly source program. The following example links object files compiled or assembled with the cc command:
cc pgm.o subs1.o subs2.o
When the cc command is used to link object files, the object files should have the suffix of .o as in the previous example.
When the cc command is used to assemble and link source files, any assembler source files must have the suffix of .s. The cc command invokes the assembler for any files having this suffix. Option flags for the as command can be directed to the assembler through the cc command. The syntax is:
The following example invokes the assembler to assemble the source program using the com assembly mode, and produces an assembler listing and an object file:
cc -c -Wa,-mcom,-l file.s
The cc command invokes the assembler and then continues processing normally. Therefore:
cc -Wa,-l,-oXfile.o file.s
will fail because the object file produced by the assembler is named Xfile.o , but the linkage editor (ld command) invoked by the cc command searches for file.o .
If no option flag is specified on the command line, the cc command uses the compiler, assembler, and link options, as well as the necessary support libraries defined in the xlc.cfg configuration file.
Note: Some option flags defined in the assembler and the linkage editor use the same letters. Therefore, if the xlc.cfg configuration file is used to define the assembler options (asopt) and the link-editor options (ldopt), duplicate letters should not occur in asopt and ldopt because the cc command is unable to distinguish the duplicate letters.
For more information on the option flags passed to the cc command, see the cc command.
Understanding Assembler Passes.
Interpreting an Assembler Listing.
Interpreting a Symbol Cross-Reference.
Subroutine Linkage Convention.
Understanding and Programming the TOC.
Running a Program.
The as command, cc command, ld command.