mbt-example-lib

An example library for MBT (mbt): one archive, mvsinfo.a, built from C, assembler and COBOL, each language doing what it does best. Its companion mbt-example-app links it into programs written in all three.

Language	Source	External name	What it does
C	src/mi_sysid.c	MISYSID	the SMF system id (CVT → SMCA)
C	src/mi_ipldt.c	MIIPLDT	the date in the CVT, 0CYYDDDF
C	src/mi_hexln.c, src/mi_hexdm.c	MIHEXLIN, MIHEXDMP	a hex and EBCDIC dump
C	src/mi_fmtdt.c, src/mi_fmtnm.c	MIFMTDAT, MIFMTNUM	C faces of the COBOL formatters
Assembler	asm/mijobn.asm	MIJOBN	the job name (PSATOLD → TCBTIO → TIOT)
Assembler	asm/mitime.asm	MITIME	TIME DEC
COBOL	cobol/mifmtd.cbl	MIFMTD	0CYYDDDF → YYYY.DDD
COBOL	cobol/mifmtn.cbl	MIFMTN	a number → ZZZ,ZZZ,ZZ9-, an edited picture

C callers include mvsinfo.h; COBOL callers COPY MIPARMS. Both ship in the archive's include/.

Who calls whom

C and the rest of MVS pass arguments differently:

• C (cc370): register 1 addresses the argument values; the last one is not marked.
• COBOL and the OS convention: register 1 addresses the argument addresses; the last one has its high-order bit set.

The library bridges them in two ways:

• The assembler routines take pointers only and drop the high-order bit. A pointer passed by C and an address passed by COBOL are then the same thing, so C, COBOL and assembler call MIJOBN and MITIME alike.
• The COBOL formatters keep the OS convention, and C reaches them through small wrappers (mi_fmtdate(), mi_fmtnum()) that pass addresses and set the bit on the last one.

C → COBOL, C → assembler, COBOL → assembler, assembler → COBOL and COBOL → COBOL work as they are. COBOL → C does not: C expects its own stack in the caller's save area, which a COBOL save area does not have. A glue routine for that is being designed in LIBC/370 (libc370#502).

Building

You need MBT 3, the CC/370 toolchain (cc370, with LIBC/370 and maclib370), and cobc370 on PATH (or named in MBT_COBC370):

mbt build        # the archive build/mvsinfo.a
mbt test         # the host test of the hex dump
mbt package      # dist/mbt-example-lib-<version>-lib.tar.gz

The project file is mbt.toml. A COBOL source in sources is translated by cobc370 into build/cobol/<stem>.asm and assembled like any other assembler source; [build] cobflags tells cobc370 where COPY finds its copybooks.