openbsd.{compat,compatHook}: init

OpenBSD does not provide a compatibility library for running
build tools on other OSes, but we still need one.
`openbsd.compat` inspired by the `freebsd.compat` package and provides
a header-only compatibility layer that can be used across multiple
openbsd build packages. The source is included in the nixpkgs tree
because it functions similarly to per-package patches.

`openbsd.compatHook` provides a build hook that can be added into
`extraNativeBuildInputs` to include `compat` in the library search
path as a system library.

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/err.h

@@ -0,0 +1,30 @@
+#pragma once
+#include_next <err.h>
+
+#include <errno.h>
+#include <stdarg.h>
+static inline void __attribute__((__format__(printf, 3, 4)))
+errc(int eval, int code, const char *fmt, ...) {
+  // verr uses the error code from errno
+  // No need to keep the old value since this is noreturn anyway
+  errno = code;
+
+  va_list args;
+  va_start(args, fmt);
+  verr(eval, fmt, args);
+  va_end(args);
+}
+
+static inline void __attribute__((__format__(printf, 2, 3)))
+warnc(int code, const char *fmt, ...) {
+  // verr uses the error code from errno
+  int old_errno = errno;
+  errno = code;
+
+  va_list args;
+  va_start(args, fmt);
+  vwarn(fmt, args);
+  va_end(args);
+
+  errno = old_errno;
+}

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/fcntl.h

@@ -0,0 +1,6 @@
+#pragma once
+#include_next <fcntl.h>
+
+// Linux doesn't let you lock during open, make these do nothing
+#define O_EXLOCK 0
+#define O_SHLOCK 0

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/sys/cdefs.h

@@ -0,0 +1,4 @@
+#include_next <sys/cdefs.h>
+
+#define __packed __attribute__((__packed__))
+#define __aligned(x) __attribute__((__aligned__(x)))

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/sys/dirent.h

@@ -0,0 +1 @@
+#include <dirent.h>

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/sys/endian.h

@@ -0,0 +1,2 @@
+// Seems to be the only header for htonl
+#include <netinet/in.h>

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/sys/types.h

@@ -0,0 +1,10 @@
+#include_next <sys/types.h>
+
+// for makedev, major, minor
+#include <sys/sysmacros.h>
+
+// For htonl, htons, etc.
+#include <arpa/inet.h>
+
+// for uint32_t etc.
+#include <stdint.h>

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/unistd.h

@@ -0,0 +1,8 @@
+#pragma once
+
+#include_next <unistd.h>
+
+// Reimplementing pledge and unvail with seccomp would be a pain,
+// so do nothing but claim they succeeded
+static int pledge(const char *, const char *) { return 0; }
+static int unveil(const char *, const char *) { return 0; }

pkgs/os-specific/bsd/openbsd/pkgs/compat/include/util.h

@@ -0,0 +1 @@
+#include <sys/types.h>

pkgs/os-specific/bsd/openbsd/pkgs/compat/package.nix

@@ -0,0 +1,16 @@
+{ runCommand, lib }:
+
+runCommand "openbsd-compat"
+  {
+    include = ./include;
+
+    meta = with lib; {
+      description = "A header-only library for running OpenBSD software on Linux";
+      platforms = lib.platforms.linux;
+      maintainers = with lib.maintainers; [ artemist ];
+    };
+  }
+  ''
+    mkdir -p $out
+    cp -R $include $out/include
+  ''

pkgs/os-specific/bsd/openbsd/pkgs/compatHook/package.nix

@@ -0,0 +1,13 @@
+{
+  stdenv,
+  makeSetupHook,
+  compat,
+}:
+
+makeSetupHook {
+  name = "openbsd-compat-hook";
+  substitutions = {
+    inherit compat;
+    inherit (stdenv.cc) suffixSalt;
+  };
+} ./setup-hook.sh

pkgs/os-specific/bsd/openbsd/pkgs/compatHook/setup-hook.sh

@@ -0,0 +1,5 @@
+useOpenBSDCompat () {
+  export NIX_CFLAGS_COMPILE_@suffixSalt@+="-I@compat@/include"
+}
+
+postHooks+=(useOpenBSDCompat)