1 files changed, 70 insertions, 0 deletions
diff --git a/src/arch/riscv/prefix/sbiprefix.S b/src/arch/riscv/prefix/sbiprefix.S
new file mode 100644
index 000000000..da3202aa2
--- /dev/null
+++ b/src/arch/riscv/prefix/sbiprefix.S
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2024 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.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+	FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL )
+
+/** @file
+ *
+ * SBI position-independent executable prefix
+ *
+ */
+
+	.section ".note.GNU-stack", "", @progbits
+	.text
+
+/* Page size */
+#define PAGE_SIZE 4096
+
+	/*
+	 * SBI entry point
+	 */
+	.section ".prefix", "ax", @progbits
+	.org 0
+	.globl	_sbi_start
+_sbi_start:
+	/* Identify temporary page table and stack space
+	 *
+	 * Assume that there is sufficient writable memory (~8kB)
+	 * directly below the device tree.
+	 */
+	li	t0, ~( PAGE_SIZE - 1 )
+	and	sp, a1, t0
+	li	t0, PAGE_SIZE
+	sub	sp, sp, t0
+	mv	a2, sp
+
+	/* Install iPXE */
+	call	install
+
+	/* Call main program */
+	call	main
+
+	/* We have no return path, since the M-mode SBI implementation
+	 * will have jumped to us by setting our start address in MEPC
+	 * and issuing an MRET instruction.
+	 *
+	 * Attempt a system reset, since there is nothing else we can
+	 * viably do at this point.
+	 */
+	j	reset_system
+	.size	_sbi_start, . - _sbi_start