[riscv] Add support for the RISC-V CPU architecture

Add support for building iPXE as a 64-bit or 32-bit RISC-V binary, for
either UEFI or Linux userspace platforms.  For example:

  # RISC-V 64-bit UEFI
  make CROSS=riscv64-linux-gnu- bin-riscv64-efi/ipxe.efi

  # RISC-V 32-bit UEFI
  make CROSS=riscv64-linux-gnu- bin-riscv32-efi/ipxe.efi

  # RISC-V 64-bit Linux
  make CROSS=riscv64-linux-gnu- bin-riscv64-linux/tests.linux
  qemu-riscv64 -L /usr/riscv64-linux-gnu/sys-root \
               ./bin-riscv64-linux/tests.linux

  # RISC-V 32-bit Linux
  make CROSS=riscv64-linux-gnu- SYSROOT=/usr/riscv32-linux-gnu/sys-root \
       bin-riscv32-linux/tests.linux
  qemu-riscv32 -L /usr/riscv32-linux-gnu/sys-root \
               ./bin-riscv32-linux/tests.linux

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

src/arch/riscv64/Makefile

@@ -0,0 +1,19 @@
+# RISCV64-specific directories containing source files
+#
+SRCDIRS		+= arch/riscv64/core
+
+# RISCV64-specific flags
+#
+CFLAGS		+= -march=rv64gc -mabi=lp64d
+ASFLAGS		+= -march=rv64gc -mabi=lp64d
+LDFLAGS		+= -m elf64lriscv
+
+# Include common RISCV Makefile
+#
+MAKEDEPS	+= arch/riscv/Makefile
+include arch/riscv/Makefile
+
+# Include platform-specific Makefile
+#
+MAKEDEPS	+= arch/riscv64/Makefile.$(PLATFORM)
+include arch/riscv64/Makefile.$(PLATFORM)

src/arch/riscv64/Makefile.efi

@@ -0,0 +1,14 @@
+# -*- makefile -*- : Force emacs to use Makefile mode
+
+# Specify EFI image builder
+#
+ELF2EFI		= $(ELF2EFI64)
+
+# Specify EFI boot file
+#
+EFI_BOOT_FILE	= bootriscv64.efi
+
+# Include generic EFI Makefile
+#
+MAKEDEPS	+= arch/riscv/Makefile.efi
+include arch/riscv/Makefile.efi

src/arch/riscv64/Makefile.linux

@@ -0,0 +1,10 @@
+# -*- makefile -*- : Force emacs to use Makefile mode
+
+# Starting virtual address
+#
+LDFLAGS += -Ttext=0x10000
+
+# Include generic Linux Makefile
+#
+MAKEDEPS += arch/riscv/Makefile.linux
+include arch/riscv/Makefile.linux

src/arch/riscv64/core/riscv64_byteswap.S

@@ -0,0 +1,64 @@
+/*
+ * 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
+ *
+ * Byte swapping
+ *
+ */
+
+	.section ".note.GNU-stack", "", @progbits
+	.text
+
+	.section ".text.riscv_swap", "ax", @progbits
+riscv_swap:
+	.globl	riscv_swap_word
+	.globl	riscv_swap_half
+	.globl	riscv_swap_byte
+riscv_swap_word:
+	/* Swap low and high words of a0 */
+	slli	t0, a0, 32
+	srli	a0, a0, 32
+	or	a0, a0, t0
+riscv_swap_half:
+	/* Swap half-words within each word of a0 */
+	ld	t1, mask16
+	slli	t2, a0, 16
+	and	a0, a0, t1
+	and	t2, t2, t1
+	srli	a0, a0, 16
+	or	a0, a0, t2
+riscv_swap_byte:
+	/* Swap bytes within each half-word of a0 */
+	ld	t3, mask8
+	slli	t4, a0, 8
+	and	a0, a0, t3
+	and	t4, t4, t3
+	srli	a0, a0, 8
+	or	a0, a0, t4
+	ret
+mask16:	.dword 0xffff0000ffff0000
+mask8:	.dword 0xff00ff00ff00ff00
+	.size	riscv_swap, . - riscv_swap

src/arch/riscv64/include/bits/profile.h

@@ -0,0 +1,28 @@
+#ifndef _BITS_PROFILE_H
+#define _BITS_PROFILE_H
+
+/** @file
+ *
+ * Profiling
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdint.h>
+
+/**
+ * Get profiling timestamp
+ *
+ * @ret timestamp	Timestamp
+ */
+static inline __attribute__ (( always_inline )) uint64_t
+profile_timestamp ( void ) {
+	uint64_t cycles;
+
+	/* Read timestamp counter */
+	__asm__ __volatile__ ( "rdcycle %0" : "=r" ( cycles ) );
+	return cycles;
+}
+
+#endif /* _BITS_PROFILE_H */

src/arch/riscv64/include/ipxe/efi/dhcparch.h

@@ -0,0 +1,20 @@
+#ifndef _IPXE_EFI_DHCPARCH_H
+#define _IPXE_EFI_DHCPARCH_H
+
+/** @file
+ *
+ * DHCP client architecture definitions
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/dhcp.h>
+
+/** DHCP client architecture */
+#define DHCP_ARCH_CLIENT_ARCHITECTURE DHCP_CLIENT_ARCHITECTURE_RISCV64
+
+/** DHCP client network device interface */
+#define DHCP_ARCH_CLIENT_NDI 1 /* UNDI */ , 3, 10 /* v3.10 */
+
+#endif /* _IPXE_EFI_DHCPARCH_H */

src/arch/riscv64/include/limits.h

@@ -0,0 +1,61 @@
+#ifndef LIMITS_H
+#define LIMITS_H	1
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/* Number of bits in a `char' */
+#define CHAR_BIT	8
+
+/* Minimum and maximum values a `signed char' can hold */
+#define SCHAR_MIN	(-128)
+#define SCHAR_MAX	127
+
+/* Maximum value an `unsigned char' can hold. (Minimum is 0.) */
+#define UCHAR_MAX	255
+
+/* Minimum and maximum values a `char' can hold */
+#define CHAR_MIN	SCHAR_MIN
+#define CHAR_MAX	SCHAR_MAX
+
+/* Minimum and maximum values a `signed short int' can hold */
+#define SHRT_MIN	(-32768)
+#define SHRT_MAX	32767
+
+/* Maximum value an `unsigned short' can hold. (Minimum is 0.) */
+#define USHRT_MAX	65535
+
+
+/* Minimum and maximum values a `signed int' can hold */
+#define INT_MIN		(-INT_MAX - 1)
+#define INT_MAX		2147483647
+
+/* Maximum value an `unsigned int' can hold. (Minimum is 0.) */
+#define UINT_MAX	4294967295U
+
+
+/* Minimum and maximum values a `signed int' can hold */
+#define INT_MAX		2147483647
+#define INT_MIN		(-INT_MAX - 1)
+
+
+/* Maximum value an `unsigned int' can hold. (Minimum is 0.) */
+#define UINT_MAX	4294967295U
+
+
+/* Minimum and maximum values a `signed long' can hold */
+#define LONG_MAX	9223372036854775807L
+#define LONG_MIN	(-LONG_MAX - 1L)
+
+/* Maximum value an `unsigned long' can hold. (Minimum is 0.) */
+#define ULONG_MAX	18446744073709551615UL
+
+/* Minimum and maximum values a `signed long long' can hold */
+#define LLONG_MAX	9223372036854775807LL
+#define LLONG_MIN	(-LONG_MAX - 1LL)
+
+
+/* Maximum value an `unsigned long long' can hold. (Minimum is 0.) */
+#define ULLONG_MAX	18446744073709551615ULL
+
+
+#endif /* LIMITS_H */