platform-support.md: document the various NetBSD targets.

This is slightly patterned after what OpenBSD has done.

This is a step along the path to reduce the number and amount
of diffs that pkgsrc carries around for rust, and this documents
also some parts which have not yet been upstreamed (mipsel-*).

src/doc/rustc/src/platform-support.md

@@ -223,13 +223,14 @@ target | std | host | notes
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
 `aarch64-unknown-hermit` | ✓ |  | ARM64 HermitCore
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
-`aarch64-unknown-netbsd` | ✓ | ✓ |
+[`aarch64-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | ARM64 NetBSD
 [`aarch64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | ARM64 OpenBSD
 `aarch64-unknown-redox` | ? |  | ARM64 Redox OS
 `aarch64-uwp-windows-msvc` | ? |  |
 `aarch64-wrs-vxworks` | ? |  |
 `aarch64_be-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (big-endian, ILP32 ABI)
 `aarch64_be-unknown-linux-gnu` | ✓ | ✓ | ARM64 Linux (big-endian)
+[`aarch64_be-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | ARM64 NetBSD (big-endian)
 [`arm64_32-apple-watchos`](platform-support/apple-watchos.md) | ✓ | | ARM Apple WatchOS 64-bit with 32-bit pointers
 [`armeb-unknown-linux-gnueabi`](platform-support/armeb-unknown-linux-gnueabi.md) | ✓ | ? | ARM BE8 the default ARM big-endian architecture since [ARMv6](https://developer.arm.com/documentation/101754/0616/armlink-Reference/armlink-Command-line-Options/--be8?lang=en).
 `armv4t-none-eabi` | * |  | ARMv4T A32
@@ -237,7 +238,7 @@ target | std | host | notes
 [`armv5te-none-eabi`](platform-support/armv5te-none-eabi.md) | * | | ARMv5TE A32
 `armv5te-unknown-linux-uclibceabi` | ? |  | ARMv5TE Linux with uClibc
 `armv6-unknown-freebsd` | ✓ | ✓ | ARMv6 FreeBSD
-`armv6-unknown-netbsd-eabihf` | ? |  |
+[`armv6-unknown-netbsd-eabihf`](platform-support/netbsd.md) | ✓ | ✓ | ARMv6 NetBSD w/hard-float
 [`armv6k-nintendo-3ds`](platform-support/armv6k-nintendo-3ds.md) | ? |  | ARMv6K Nintendo 3DS, Horizon (Requires devkitARM toolchain)
 `armv7-apple-ios` | ✓ |  | ARMv7 iOS, Cortex-a8
 [`armv7-sony-vita-newlibeabihf`](platform-support/armv7-sony-vita-newlibeabihf.md) | ? |  | ARM Cortex-A9 Sony PlayStation Vita (requires VITASDK toolchain)
@@ -245,7 +246,7 @@ target | std | host | notes
 [`armv7-unknown-linux-uclibceabi`](platform-support/armv7-unknown-linux-uclibceabi.md) | ✓ | ✓ | ARMv7 Linux with uClibc, softfloat
 [`armv7-unknown-linux-uclibceabihf`](platform-support/armv7-unknown-linux-uclibceabihf.md) | ✓ | ? | ARMv7 Linux with uClibc, hardfloat
 `armv7-unknown-freebsd` | ✓ | ✓ | ARMv7 FreeBSD
-`armv7-unknown-netbsd-eabihf` | ✓ | ✓ |
+[`armv7-unknown-netbsd-eabihf`](platform-support/netbsd.md) | ✓ | ✓ | ARMv7 NetBSD w/hard-float
 `armv7-wrs-vxworks-eabihf` | ? |  |
 [`armv7a-kmc-solid_asp3-eabi`](platform-support/kmc-solid.md) | ✓ |  | ARM SOLID with TOPPERS/ASP3
 [`armv7a-kmc-solid_asp3-eabihf`](platform-support/kmc-solid.md) | ✓ |  | ARM SOLID with TOPPERS/ASP3, hardfloat
@@ -258,10 +259,11 @@ target | std | host | notes
 `hexagon-unknown-linux-musl` | ? |  |
 `i386-apple-ios` | ✓ |  | 32-bit x86 iOS
 [`i586-pc-nto-qnx700`](platform-support/nto-qnx.md) | * |  | 32-bit x86 QNX Neutrino 7.0 RTOS |
+[`i586-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/i386 restricted to Pentium insns
 `i686-apple-darwin` | ✓ | ✓ | 32-bit macOS (10.7+, Lion+)
 `i686-pc-windows-msvc` | * |  | 32-bit Windows XP support
 `i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku
-`i686-unknown-netbsd` | ✓ | ✓ | NetBSD/i386 with SSE2
+[`i686-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/i386 with SSE2
 [`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD
 `i686-uwp-windows-gnu` | ? |  |
 `i686-uwp-windows-msvc` | ? |  |
@@ -273,6 +275,7 @@ target | std | host | notes
 `mipsel-sony-psp` | * |  | MIPS (LE) Sony PlayStation Portable (PSP)
 [`mipsel-sony-psx`](platform-support/mipsel-sony-psx.md) | * |  | MIPS (LE) Sony PlayStation 1 (PSX)
 `mipsel-unknown-linux-uclibc` | ✓ |  | MIPS (LE) Linux with uClibc
+[`mipsel-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | MIPS (LE) on NetBSD, requires mips32 CPU
 `mipsel-unknown-none` | * |  | Bare MIPS (LE) softfloat
 `mipsisa32r6-unknown-linux-gnu` | ? |  |
 `mipsisa32r6el-unknown-linux-gnu` | ? |  |
@@ -281,7 +284,7 @@ target | std | host | notes
 `msp430-none-elf` | * |  | 16-bit MSP430 microcontrollers
 `powerpc-unknown-linux-gnuspe` | ✓ |  | PowerPC SPE Linux
 `powerpc-unknown-linux-musl` | ? |  |
-`powerpc-unknown-netbsd` | ✓ | ✓ |
+[`powerpc-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD 32-bit powerpc systems
 `powerpc-unknown-openbsd` | ? |  |
 `powerpc-wrs-vxworks-spe` | ? |  |
 `powerpc-wrs-vxworks` | ? |  |
@@ -304,7 +307,7 @@ target | std | host | notes
 [`riscv64gc-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/riscv64
 `s390x-unknown-linux-musl` |  |  | S390x Linux (kernel 3.2, MUSL)
 `sparc-unknown-linux-gnu` | ✓ |  | 32-bit SPARC Linux
-`sparc64-unknown-netbsd` | ✓ | ✓ | NetBSD/sparc64
+[`sparc64-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/sparc64
 [`sparc64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/sparc64
 `thumbv4t-none-eabi` | * |  | ARMv4T T32
 [`thumbv5te-none-eabi`](platform-support/armv5te-none-eabi.md) | * | | ARMv5TE T32

src/doc/rustc/src/platform-support/netbsd.md

@@ -0,0 +1,108 @@
+# \*-unknown-netbsd
+
+**Tier: 3**
+
+[NetBSD] multi-platform 4.4BSD-based UNIX-like operating system.
+
+[NetBSD]: https://www.NetBSD.org/
+
+The target names follow this format: `$ARCH-unknown-netbsd{-$SUFFIX}`,
+where `$ARCH` specifies the target processor architecture and
+`-$SUFFIX` (optional) might indicate the ABI. The following targets
+are currently defined running NetBSD:
+
+|          Target name           | NetBSD Platform |
+|--------------------------------|-----------------|
+| `amd64-unknown-netbsd`         | [amd64 / x86_64 systems](https://wiki.netbsd.org/ports/amd64/) |
+| `armv7-unknown-netbsd-eabihf`  | [32-bit ARMv7 systems with hard-float](https://wiki.netbsd.org/ports/evbarm/) |
+| `armv6-unknown-netbsd-eabihf`  | [32-bit ARMv6 systems with hard-float](https://wiki.netbsd.org/ports/evbarm/) |
+| `aarch64-unknown-netbsd`       | [64-bit ARM systems, little-endian](https://wiki.netbsd.org/ports/evbarm/) |
+| `aarch64_be-unknown-netbsd`    | [64-bit ARM systems, big-endian](https://wiki.netbsd.org/ports/evbarm/) |
+| `i586-unknown-netbsd`          | [32-bit i386, restricted to Pentium](https://wiki.netbsd.org/ports/i386/) |
+| `i686-unknown-netbsd`          | [32-bit i386 with SSE](https://wiki.netbsd.org/ports/i386/) |
+| `mipsel-unknown-netbsd`        | [32-bit mips, requires mips32 cpu support](https://wiki.netbsd.org/ports/evbmips/) |
+| `powerpc-unknown-netbsd`       | [Various 32-bit PowerPC systems, e.g. MacPPC](https://wiki.netbsd.org/ports/macppc/) |
+| `sparc64-unknown-netbsd`       | [Sun UltraSPARC systems](https://wiki.netbsd.org/ports/sparc64/) |
+
+All use the "native" `stdc++` library which goes along with the natively
+supplied GNU C++ compiler for the given OS version.  Many of the bootstraps
+are built for NetBSD 9.x, although some exceptions exist (some
+are built for NetBSD 8.x but also work on newer OS versions).
+
+
+## Designated Developers
+
+- [@he32](https://github.com/he32), `he@NetBSD.org`
+- [NetBSD/pkgsrc-wip's rust](https://github.com/NetBSD/pkgsrc-wip/blob/master/rust/Makefile) maintainer (see MAINTAINER variable). This package is part of "pkgsrc work-in-progress" and is used for deployment and testing of new versions of rust
+- [NetBSD's pkgsrc lang/rust](https://github.com/NetBSD/pkgsrc/tree/trunk/lang/rust) for the "proper" package in pkgsrc.
+- [NetBSD's pkgsrc lang/rust-bin](https://github.com/NetBSD/pkgsrc/tree/trunk/lang/rust-bin) which re-uses the bootstrap kit as a binary distribution and therefore avoids the rather protracted native build time of rust itself
+
+Fallback to pkgsrc-users@NetBSD.org, or fault reporting via NetBSD's
+bug reporting system.
+
+## Requirements
+
+The `amd64-unknown-netbsd` artifacts is being distributed by the
+rust project.
+
+The other targets are built by the designated developers (see above),
+and the targets are initially cross-compiled, but many if not most
+of them are also built natively as part of testing.
+
+
+## Building
+
+The default build mode for the packages is a native build.
+
+
+## Cross-compilation
+
+These targets can be cross-compiled, and we do that via the pkgsrc
+package(s).
+
+Cross-compilation typically requires the "tools" and "dest" trees
+resulting from a normal cross-build of NetBSD itself, ref. our main
+build script, `build.sh`.
+
+See e.g. [do-cross.mk
+Makefile](https://github.com/NetBSD/pkgsrc/tree/trunk/lang/rust/do-cross.mk)
+for the Makefile used to cross-build all the above NetBSD targets
+(except for the `amd64` target).
+
+The major option for the rust build is whether to build rust with
+the LLVM rust carries in its distribution, or use the LLVM package
+installed from pkgsrc.  The `PKG_OPTIONS.rust` option is
+`rust-internal-llvm`, ref.  [the rust package's options.mk make
+fragment](https://github.com/NetBSD/pkgsrc/blob/trunk/lang/rust/options.mk).
+It defaults to being set for a few of the above platforms, for
+various reasons (see comments), but is otherwise unset and therefore
+indicates use of the pkgsrc LLVM.
+
+
+## Testing
+
+The Rust testsuite could presumably be run natively.
+
+For the systems where the maintainer can build natively, the rust
+compiler itself is re-built natively.  This involves the rust compiler
+being re-built with the newly self-built rust compiler, so excercises
+the result quite extensively.
+
+Additionally, for some systems we build `librsvg`, and for the more
+capable systems we build and test `firefox` (amd64, i386, aarch64).
+
+
+## Building Rust programs
+
+Rust ships pre-compiled artifacts for the `amd64-unknown-netbsd`
+target.
+
+For the other systems mentioned above, using the `pkgsrc` route is
+probably the easiest, possibly via the `rust-bin` package to save
+time, see the `RUST_TYPE` variable from the `rust.mk` Makefile
+fragment.
+
+The pkgsrc rust package has a few files to assist with building
+pkgsrc packages written in rust, ref. the `rust.mk` and `cargo.mk`
+Makefile fragments in the `lang/rust` package.
+