cc370

A host-native cross-toolchain for MVS 3.8j (TK4-, TK5, MVS/CE): compile, assemble, link and package MVS programs entirely on the host (macOS / Linux), so the only thing that touches the mainframe is the finished load module.

cc370 hello.c -o hello                       # -> hello : an MVS load module (LMOD)
cc370 hello.c -o hello -flinker-output=xmit  # -> hello + hello.xmit : compile+assemble+link+package

-o always writes the load-module member; -flinker-output=xmit additionally emits hello.xmit (and =iebcopy an hello.iebcopy unloaded-PDS image). That hello.xmit ships to MVS and is installed into a load library with one RECV370 step — no IFOX00, no IEWL, no IEBCOPY, no JCL round-trip.

The tools

Tool	Role	Built from
cc370	the driver + C → i370 HLASM compiler (cc370/gcc/)	a GCC 3.4.6 fork for the i370-ibm-mvspdp target (TARGET_PDPMAC)
as370	.s/.asm → OS/360 object deck — byte-identical to IBM's IFOX00	as370/src/as370.c
ld370	object decks → MVS load module (replaces IEWL) + automatic library call + -iebcopy/-xmit host→MVS transport	ld370/src/ld370.c
ar370	object decks → .a archive with an ESD symbol index	ar370/src/ar370.c
file370	read-only inspector — identify + analyze any of the formats above (file/objdump for the toolchain)	file370/src/file370.c

cc370 is the single front-end; as370/ld370/ar370 are ordinary binaries it drives (and which you can also run standalone); file370 is a standalone inspector that reads the formats the others write. The C library it links against is libc370, installed into the cc370 sysroot — see Sysroot below.

Build & install

GCC 3.4.6 is old K&R-ish C; a modern clang/gcc host must be told not to error on it. The top-level Makefile wraps the whole thing:

make            # build the whole toolchain: cc370 + as370/ld370/ar370 + man pages
make tools      # only the three tools (fast; skips the slow compiler build)
make compiler   # just the driver (cc370) + the compiler proper (cc1), out-of-tree in build/
make install    # build (if needed) + install everything under $(PREFIX) (default ~/.local)

Knobs: PREFIX (default ~/.local), TRIPLE (default cc370), VERSION (default 1.0.0). After make install you get:

<prefix>/bin/cc370                          the driver
<prefix>/bin/{as370,ld370,ar370}            symlinks -> ../cc370/bin/* (PATH access)
<prefix>/libexec/cc370/1.0.0/cc1            the compiler proper (driver-private)
<prefix>/libexec/cc370/1.0.0/{as,ld,ar}     symlinks beside cc1; the driver's tooldir
<prefix>/cc370/bin/{as370,ld370,ar370}      the real tool binaries
<prefix>/cc370/{include,lib,macros}         the libc370 sysroot (headers, libc.a, crt*.o, macros)
<prefix>/lib/cc370/1.0.0/                    empty: GCC's libsubdir, but required (see below)

The target name is cc370 (a config.sub alias for the real i370-ibm-mvspdp backend); nothing user-facing carries the old triple. Everything for the target lives in one cc370/ tree; only the user-facing binaries sit on PATH. The empty lib/cc370/1.0.0/ is GCC's libsubdir: it holds no libgcc (we ship none), but the driver locates the whole cc370/ sysroot — both <stdio.h> and -lc — via a path relative to it, so it must exist. Builds on x86-64 and ARM64.

Sysroot — where cc370 finds the libc

cc370 searches <prefix>/cc370/{include,lib} by default (the cc370 component is the target name, from -dumpmachine). libc370 drops its headers, libc.a, the crt0/1/m.o startfiles and the assembler macros all under <prefix>/cc370/ (include, lib, macros); as370, whose real binary lives in <prefix>/cc370/bin, finds the macros via its <exedir>/../macros default. After that the toolchain is self-contained:

make -C ../libc370 install                   # populate the sysroot once
cc370 hello.c -o hello -flinker-output=xmit  # no -I, no -L, no -lc needed

Optimization: -O1 only

-O2/-Os/-O3 are unsafe on this backend. At -O2+ the -funit-at-a-time DCE drops static tables whose address is held by a global pointer → dangling address constants → assembler RC=8; -Os additionally miscompiles the rexx parser (loops → S322). -O1 is validated correct (rexx370 TSTALLB 84/84, 0 ABEND). This — not any memory limit — is the reason for "-O1 only".

Layout

cc370/             the GCC 3.4.6 fork — the compiler (driver + cc1)
  gcc/config/i370/   the i370/mvspdp target backend — check here first for codegen bugs
  gcc/ libiberty/ intl/ include/ config/   GCC core + build deps, largely upstream
as370/   src/ include/ tests/   as370 — host-native MVS assembler  (as370/README.md)
ld370/   src/ tests/            ld370 — host-native linker (replaces IEWL)
ar370/   src/                   ar370 — .a archiver (ld370 autocalls against it)
file370/ src/                   file370 — format inspector (file/objdump for the formats above)
docs/                           object / load-module / unload / xmit formats + roadmap
Makefile                        make (whole toolchain) / make tools / make compiler

Deep dives: CLAUDE.md (architecture + gotchas), as370/README.md, and docs/ (the on-the-wire formats).

Provenance

The compiler is a fork of GCC 3.4.6 — the last GCC to carry the i370 machine definition — for the i370-ibm-mvspdp target (TARGET_PDPMAC: HLASM/EBCDIC, COPY PDPTOP / PDPPRLG / PDPEPIL, libc370-compatible calling conventions), slimmed to that one target.

It descends from the gccmvs / i370-gcc line (Paul Edwards, Dave Pitts, and others). Specifically, this tree is a snapshot of mvslovers/i370-gcc @ feature/ebcdic-char-constants (commit 0710af0c), brought in as v2.0 because the upstream PRs to linas went unanswered — so the compiler is developed against the ecosystem's own requirements from here on. The earlier GCC 3.2.3-based generation is the frozen mvslovers/c2asm370 repo (v1.x), kept as a fallback for projects still on the old name.

What this snapshot carries over stock GCC 3.4.6:

• EBCDIC charset (CP037 + ecosystem NEL): char constants and string literals map to CP037; \n maps to EBCDIC NEL 0x15 (byte-identical to the ecosystem httpd cp037_atoe/cp037_etoa, so it matches mvsMF upload and HTTP output); \x../\NNN escapes stay binary-literal.
• Codegen for IFOX00: fixed-column assembler text, valid MVS symbol names for private statics, signed 32-bit literals; the asm()-extern address-of fix.
• Host portability: builds on macOS and Linux, x86-64 and ARM64, modern clang/gcc-14 hosts.
• Slimmed to i370: the tree was cut from ~20 640 to ~1 100 tracked files (other GCC targets, other-language front ends, the test suite, other-language runtimes), then the leftover build cruft (changelogs, contrib, stale objects).

Building the compiler by hand

make compiler wraps this; the equivalent direct invocation (the GCC 3.4.6 fork needs the old-C -w/-Wno-* flags on a modern host):

CF="-g -O0 -fcommon -std=gnu89 -Wno-implicit-int -Wno-implicit-function-declaration \
    -Wno-int-conversion -Wno-error -Wno-return-type -Wno-deprecated-non-prototype"
mkdir build && cd build
CFLAGS="$CF" CFLAGS_FOR_BUILD="$CF" ../cc370/configure \
  --target=i370-ibm-mvspdp --enable-languages=c \
  --disable-threads --disable-nls --disable-shared --without-headers
make all-gcc CFLAGS="$CF" CFLAGS_FOR_BUILD="$CF"   # -> build/gcc/{cc1,xgcc}

Maintained by the mvslovers community.