[linux] Use host glibc system call wrappers

When building as a Linux userspace application, iPXE currently
implements its own system calls to the host kernel rather than relying
on the host's C library.  The output binary is statically linked and
has no external dependencies.

This matches the general philosophy of other platforms on which iPXE
runs, since there are no external libraries available on either BIOS
or UEFI bare metal.  However, it would be useful for the Linux
userspace application to be able to link against host libraries such
as libslirp.

Modify the build process to perform a two-stage link: first picking
out the requested objects in the usual way from blib.a but with
relocations left present, then linking again with a helper object to
create a standard hosted application.  The helper object provides the
standard main() entry point and wrappers for the Linux system calls
required by the iPXE Linux drivers and interface code.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/src/interface/linux/linuxprefix.c b/src/interface/linux/linuxprefix.c
new file mode 100644
index 000000000..f38236202
--- /dev/null
+++ b/src/interface/linux/linuxprefix.c
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2021 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#include <stdlib.h>
+#include <ipxe/linux_api.h>
+
+/**
+ * Linux entry point
+ *
+ * @v argc		Argument count
+ * @v argv		Argument list
+ * @ret rc		Return status code
+ */
+int __asmcall _linux_start ( int argc, char **argv ) {
+
+	/* Store command-line arguments */
+	linux_argc = argc;
+	linux_argv = argv;
+
+	/* Run iPXE */
+	return main();
+}