bsd-user: Define RISC-V system call structures and constants

Introduced definitions for the RISC-V system call interface, including
the 'target_pt_regs' structure that outlines the register storage
layout during a system call.
Added constants for hardware machine identifiers.

Signed-off-by: Mark Corbin <mark@dibsco.co.uk>
Signed-off-by: Ajeet Singh <itachis@FreeBSD.org>
Co-authored-by: Jessica Clarke <jrtc27@jrtc27.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20240916155119.14610-12-itachis@FreeBSD.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
diff --git a/bsd-user/riscv/target_syscall.h b/bsd-user/riscv/target_syscall.h
new file mode 100644
index 0000000..e7e5231
--- /dev/null
+++ b/bsd-user/riscv/target_syscall.h
@@ -0,0 +1,38 @@
+/*
+ *  RISC-V system call definitions
+ *
+ *  Copyright (c) Mark Corbin
+ *
+ *  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
+ *  (at your option) 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef BSD_USER_RISCV_TARGET_SYSCALL_H
+#define BSD_USER_RISCV_TARGET_SYSCALL_H
+
+/*
+ * struct target_pt_regs defines the way the registers are stored on the stack
+ * during a system call.
+ */
+
+struct target_pt_regs {
+    abi_ulong regs[32];
+    abi_ulong sepc;
+};
+
+#define UNAME_MACHINE "riscv64"
+
+#define TARGET_HW_MACHINE       "riscv"
+#define TARGET_HW_MACHINE_ARCH  UNAME_MACHINE
+
+#endif /* BSD_USER_RISCV_TARGET_SYSCALL_H */