[build] Allow for per-architecture cross-compilation prefixes

We currently require the variable CROSS (or CROSS_COMPILE) to be set
to specify the global cross-compilation prefix.  This becomes
cumbersome when developing across multiple CPU architectures,
requiring frequent editing of build command lines and preventing
incompatible architectures from being built with a single command.

Allow a default cross-compilation prefix for each architecture to be
specified via the CROSS_COMPILE_<arch> variables.  These may then be
provided as environment variables, e.g. using

  export CROSS_COMPILE_arm32=arm-linux-gnu-
  export CROSS_COMPILE_arm64=aarch64-linux-gnu-
  export CROSS_COMPILE_loong64=loongarch64-linux-gnu-
  export CROSS_COMPILE_riscv32=riscv64-linux-gnu-
  export CROSS_COMPILE_riscv64=riscv64-linux-gnu-

This change requires some portions of the Makefile to be rearranged,
to allow for the fact that $(CROSS_COMPILE) may not have been set
until the build directory has been parsed to determine the CPU
architecture.

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

src/Makefile

@@ -26,16 +26,16 @@ PRINTF		:= printf
 PERL		:= perl
 PYTHON		:= python
 TRUE		:= true
-CC		:= $(CROSS_COMPILE)gcc
-CPP		:= $(CC) -E
-AS		:= $(CROSS_COMPILE)as
-LD		:= $(CROSS_COMPILE)ld
-SIZE		:= $(CROSS_COMPILE)size
-AR		:= $(CROSS_COMPILE)ar
-RANLIB		:= $(CROSS_COMPILE)ranlib
-OBJCOPY		:= $(CROSS_COMPILE)objcopy
-NM		:= $(CROSS_COMPILE)nm
-OBJDUMP		:= $(CROSS_COMPILE)objdump
+CC		= $(CROSS_COMPILE)gcc
+CPP		= $(CC) -E
+AS		= $(CROSS_COMPILE)as
+LD		= $(CROSS_COMPILE)ld
+SIZE		= $(CROSS_COMPILE)size
+AR		= $(CROSS_COMPILE)ar
+RANLIB		= $(CROSS_COMPILE)ranlib
+OBJCOPY		= $(CROSS_COMPILE)objcopy
+NM		= $(CROSS_COMPILE)nm
+OBJDUMP		= $(CROSS_COMPILE)objdump
 OPENSSL		:= openssl
 CSPLIT		:= csplit
 PARSEROM	:= ./util/parserom.pl

src/Makefile.housekeeping

@@ -3,6 +3,20 @@
 # This file contains various boring housekeeping functions that would
 # otherwise seriously clutter up the main Makefile.
 
+###############################################################################
+#
+# Make syntax does not allow use of comma or space in certain places.
+# This ugly workaround is suggested in the manual.
+#
+COMMA	:= ,
+EMPTY	:=
+SPACE	:= $(EMPTY) $(EMPTY)
+HASH	:= \#
+define NEWLINE
+
+
+endef
+
 ###############################################################################
 #
 # Find a usable "echo -e" substitute.
@@ -68,56 +82,6 @@ HOST_OS		:= $(shell uname -s)
 hostos :
 	@$(ECHO) $(HOST_OS)
 
-###############################################################################
-#
-# Determine compiler
-
-CCDEFS		:= $(shell $(CC) -E -x c -c /dev/null -dM | cut -d" " -f2)
-ccdefs:
-	@$(ECHO) $(CCDEFS)
-
-ifeq ($(filter __GNUC__,$(CCDEFS)),__GNUC__)
-CCTYPE		:= gcc
-endif
-cctype:
-	@$(ECHO) $(CCTYPE)
-
-###############################################################################
-#
-# Check for tools that can cause failed builds
-#
-
-ifeq ($(CCTYPE),gcc)
-GCC_2_96_BANNER := $(shell $(CC) -v 2>&1 | grep -is 'gcc version 2\.96')
-ifneq ($(GCC_2_96_BANNER),)
-$(warning gcc 2.96 is unsuitable for compiling iPXE)
-$(warning Use gcc 2.95 or a newer version instead)
-$(error Unsuitable build environment found)
-endif
-endif
-
-PERL_UNICODE_CHECK := $(shell $(PERL) -e 'use bytes; print chr(255)' | wc -c)
-ifeq ($(PERL_UNICODE_CHECK),2)
-$(warning Your Perl version has a Unicode handling bug)
-$(warning Execute this command before building iPXE:)
-$(warning export LANG=$${LANG%.UTF-8})
-$(error Unsuitable build environment found)
-endif
-
-LD_GOLD_BANNER := $(shell $(LD) -v 2>&1 | grep 'GNU gold')
-ifneq ($(LD_GOLD_BANNER),)
-$(warning GNU gold is unsuitable for building iPXE)
-$(warning Use GNU ld instead)
-$(error Unsuitable build environment found)
-endif
-
-OBJCOPY_ETC_BANNER := $(shell $(OBJCOPY) --version | grep 'elftoolchain')
-ifneq ($(OBJCOPY_ETC_BANNER),)
-$(warning The elftoolchain objcopy is unsuitable for building iPXE)
-$(warning Use binutils objcopy instead)
-$(error Unsuitable build environment found)
-endif
-
 ###############################################################################
 #
 # Check if $(eval ...) is available to use
@@ -130,74 +94,6 @@ endif
 eval :
 	@$(ECHO) $(HAVE_EVAL)
 
-###############################################################################
-#
-# Check for various tool workarounds
-#
-
-WORKAROUND_CFLAGS :=
-WORKAROUND_ASFLAGS :=
-WORKAROUND_LDFLAGS :=
-
-# Make syntax does not allow use of comma or space in certain places.
-# This ugly workaround is suggested in the manual.
-#
-COMMA	:= ,
-EMPTY	:=
-SPACE	:= $(EMPTY) $(EMPTY)
-HASH	:= \#
-define NEWLINE
-
-
-endef
-
-# gcc 4.4 generates .eh_frame sections by default, which distort the
-# output of "size".  Inhibit this.
-#
-ifeq ($(CCTYPE),gcc)
-CFI_TEST = $(CC) -fno-dwarf2-cfi-asm -fno-exceptions -fno-unwind-tables \
-		 -fno-asynchronous-unwind-tables -x c -c /dev/null \
-		 -o /dev/null >/dev/null 2>&1
-CFI_FLAGS := $(shell $(CFI_TEST) && \
-	       $(ECHO) '-fno-dwarf2-cfi-asm -fno-exceptions ' \
-		       '-fno-unwind-tables -fno-asynchronous-unwind-tables')
-WORKAROUND_CFLAGS += $(CFI_FLAGS)
-endif
-
-# gcc 4.6 generates spurious warnings if -Waddress is in force.
-# Inhibit this.
-#
-ifeq ($(CCTYPE),gcc)
-WNA_TEST = $(CC) -Waddress -x c -c /dev/null -o /dev/null >/dev/null 2>&1
-WNA_FLAGS := $(shell $(WNA_TEST) && $(ECHO) '-Wno-address')
-WORKAROUND_CFLAGS += $(WNA_FLAGS)
-
-# gcc 8.0 generates warnings for certain suspect string operations. Our
-# sources have been vetted for correct usage.  Turn off these warnings.
-#
-WNST_TEST = $(CC) -Wstringop-truncation -x c -c /dev/null -o /dev/null \
-		  >/dev/null 2>&1
-WNST_FLAGS := $(shell $(WNST_TEST) && $(ECHO) '-Wno-stringop-truncation')
-WORKAROUND_CFLAGS += $(WNST_FLAGS)
-
-# gcc 9.1 generates warnings for taking address of packed member which
-# may result in an unaligned pointer value.  Inhibit the warnings.
-#
-WNAPM_TEST = $(CC) -Wno-address-of-packed-member -x c -c /dev/null \
-		   -o /dev/null >/dev/null 2>&1
-WNAPM_FLAGS := $(shell $(WNAPM_TEST) && \
-		 $(ECHO) '-Wno-address-of-packed-member')
-WORKAROUND_CFLAGS += $(WNAPM_FLAGS)
-endif
-
-# Some versions of gas choke on division operators, treating them as
-# comment markers.  Specifying --divide will work around this problem,
-# but isn't available on older gas versions.
-#
-DIVIDE_TEST = $(AS) --divide /dev/null -o /dev/null 2>/dev/null
-DIVIDE_FLAGS := $(shell $(DIVIDE_TEST) && $(ECHO) '--divide')
-WORKAROUND_ASFLAGS += $(DIVIDE_FLAGS)
-
 ###############################################################################
 #
 # Build verbosity
@@ -284,7 +180,7 @@ ifeq ($(wildcard $(BIN)),)
 $(shell $(MKDIR) -p $(BIN))
 endif
 
-# Target to allow e.g. "make bin-efi arch"
+# Target to allow e.g. "make bin-x86_64-efi arch"
 #
 $(BIN) :
 	@# Do nothing, silently
@@ -333,8 +229,13 @@ else
 BIN_AP		:= $(BIN_APS)
 BIN_SECUREBOOT	:= 0
 endif
-BIN_PLATFORM	:= $(lastword $(BIN_AP))
-BIN_ARCH	:= $(wordlist 2,$(words $(BIN_AP)),discard $(BIN_AP))
+ifeq ($(BIN_AP),efi)
+BIN_ARCH	:= i386
+BIN_PLATFORM	:= efi
+else
+BIN_ARCH	:= $(word 1,$(BIN_AP))
+BIN_PLATFORM	:= $(word 2,$(BIN_AP))
+endif
 
 # Determine build architecture
 DEFAULT_ARCH	:= i386
@@ -345,8 +246,12 @@ arch :
 .PHONY : arch
 
 # Determine build platform
-DEFAULT_PLATFORM := pcbios
-PLATFORM	:= $(firstword $(BIN_PLATFORM) $(DEFAULT_PLATFORM))
+DEFAULT_PLATFORM_i386 := pcbios
+DEFAULT_PLATFORM_x86_64 := pcbios
+DEFAULT_PLATFORM_riscv32 := sbi
+DEFAULT_PLATFORM_riscv64 := sbi
+DEFAULT_PLATFORM := $(DEFAULT_PLATFORM_$(ARCH))
+PLATFORM	:= $(firstword $(BIN_PLATFORM) $(DEFAULT_PLATFORM) none)
 CFLAGS		+= -DPLATFORM=$(PLATFORM) -DPLATFORM_$(PLATFORM)
 platform :
 	@$(ECHO) $(PLATFORM)
@@ -358,9 +263,124 @@ CFLAGS		+= -DSECUREBOOT=$(SECUREBOOT)
 secureboot :
 	@$(ECHO) $(SECUREBOOT)
 
+# Set cross-compilation prefix automatically if not specified
+ifeq ($(CROSS_COMPILE),)
+CROSS_COMPILE	:= $(CROSS_COMPILE_$(ARCH))
+endif
+
 endif # defined(BIN)
 
+###############################################################################
+#
+# Determine compiler
+
+CCDEFS		:= $(shell $(CC) -E -x c -c /dev/null -dM | cut -d" " -f2)
+ccdefs:
+	@$(ECHO) $(CCDEFS)
+
+ifeq ($(filter __GNUC__,$(CCDEFS)),__GNUC__)
+CCTYPE		:= gcc
+endif
+cctype:
+	@$(ECHO) $(CCTYPE)
+
+###############################################################################
+#
+# Check for tools that can cause failed builds
+#
+
+ifeq ($(CCTYPE),gcc)
+GCC_2_96_BANNER := $(shell $(CC) -v 2>&1 | grep -is 'gcc version 2\.96')
+ifneq ($(GCC_2_96_BANNER),)
+$(warning gcc 2.96 is unsuitable for compiling iPXE)
+$(warning Use gcc 2.95 or a newer version instead)
+$(error Unsuitable build environment found)
+endif
+endif
+
+PERL_UNICODE_CHECK := $(shell $(PERL) -e 'use bytes; print chr(255)' | wc -c)
+ifeq ($(PERL_UNICODE_CHECK),2)
+$(warning Your Perl version has a Unicode handling bug)
+$(warning Execute this command before building iPXE:)
+$(warning export LANG=$${LANG%.UTF-8})
+$(error Unsuitable build environment found)
+endif
+
+LD_GOLD_BANNER := $(shell $(LD) -v 2>&1 | grep 'GNU gold')
+ifneq ($(LD_GOLD_BANNER),)
+$(warning GNU gold is unsuitable for building iPXE)
+$(warning Use GNU ld instead)
+$(error Unsuitable build environment found)
+endif
+
+OBJCOPY_ETC_BANNER := $(shell $(OBJCOPY) --version | grep 'elftoolchain')
+ifneq ($(OBJCOPY_ETC_BANNER),)
+$(warning The elftoolchain objcopy is unsuitable for building iPXE)
+$(warning Use binutils objcopy instead)
+$(error Unsuitable build environment found)
+endif
+
+###############################################################################
+#
+# Check for various tool workarounds
+#
+
+WORKAROUND_CFLAGS :=
+WORKAROUND_ASFLAGS :=
+WORKAROUND_LDFLAGS :=
+
+# gcc 4.4 generates .eh_frame sections by default, which distort the
+# output of "size".  Inhibit this.
+#
+ifeq ($(CCTYPE),gcc)
+CFI_TEST = $(CC) -fno-dwarf2-cfi-asm -fno-exceptions -fno-unwind-tables \
+		 -fno-asynchronous-unwind-tables -x c -c /dev/null \
+		 -o /dev/null >/dev/null 2>&1
+CFI_FLAGS := $(shell $(CFI_TEST) && \
+	       $(ECHO) '-fno-dwarf2-cfi-asm -fno-exceptions ' \
+		       '-fno-unwind-tables -fno-asynchronous-unwind-tables')
+WORKAROUND_CFLAGS += $(CFI_FLAGS)
+endif
+
+# gcc 4.6 generates spurious warnings if -Waddress is in force.
+# Inhibit this.
+#
+ifeq ($(CCTYPE),gcc)
+WNA_TEST = $(CC) -Waddress -x c -c /dev/null -o /dev/null >/dev/null 2>&1
+WNA_FLAGS := $(shell $(WNA_TEST) && $(ECHO) '-Wno-address')
+WORKAROUND_CFLAGS += $(WNA_FLAGS)
+
+# gcc 8.0 generates warnings for certain suspect string operations. Our
+# sources have been vetted for correct usage.  Turn off these warnings.
+#
+WNST_TEST = $(CC) -Wstringop-truncation -x c -c /dev/null -o /dev/null \
+		  >/dev/null 2>&1
+WNST_FLAGS := $(shell $(WNST_TEST) && $(ECHO) '-Wno-stringop-truncation')
+WORKAROUND_CFLAGS += $(WNST_FLAGS)
+
+# gcc 9.1 generates warnings for taking address of packed member which
+# may result in an unaligned pointer value.  Inhibit the warnings.
+#
+WNAPM_TEST = $(CC) -Wno-address-of-packed-member -x c -c /dev/null \
+		   -o /dev/null >/dev/null 2>&1
+WNAPM_FLAGS := $(shell $(WNAPM_TEST) && \
+		 $(ECHO) '-Wno-address-of-packed-member')
+WORKAROUND_CFLAGS += $(WNAPM_FLAGS)
+endif
+
+# Some versions of gas choke on division operators, treating them as
+# comment markers.  Specifying --divide will work around this problem,
+# but isn't available on older gas versions.
+#
+DIVIDE_TEST = $(AS) --divide /dev/null -o /dev/null 2>/dev/null
+DIVIDE_FLAGS := $(shell $(DIVIDE_TEST) && $(ECHO) '--divide')
+WORKAROUND_ASFLAGS += $(DIVIDE_FLAGS)
+
+###############################################################################
+#
 # Include architecture-specific Makefile
+#
+
 ifdef ARCH
 MAKEDEPS	+= arch/$(ARCH)/Makefile
 include arch/$(ARCH)/Makefile

src/arch/riscv/Makefile

@@ -11,6 +11,7 @@ INCDIRS		:= arch/$(ARCH)/include arch/riscv/include $(INCDIRS)
 #
 SRCDIRS		+= arch/riscv/core
 SRCDIRS		+= arch/riscv/interface/sbi
+SRCDIRS		+= arch/riscv/prefix
 
 # RISCV-specific flags
 #

src/arch/riscv/Makefile.sbi

@@ -0,0 +1,16 @@
+# -*- makefile -*- : Force emacs to use Makefile mode
+
+# Build a position-independent executable, with relocations required
+# only for data values.  Runtime relocations are applied by the
+# prefix code.
+#
+CFLAGS		+= -mcmodel=medany -fpie
+LDFLAGS		+= -pie --no-dynamic-linker
+
+# Linker script
+#
+LDSCRIPT	= arch/riscv/scripts/sbi.lds
+
+# Media types
+#
+MEDIA		+= sbi

src/arch/riscv/core/stack.S

@@ -0,0 +1,45 @@
+/*
+ * 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
+ *
+ * Internal stack
+ *
+ */
+
+	.section ".note.GNU-stack", "", @progbits
+	.text
+
+#define STACK_ALIGN 16
+
+#define STACK_SIZE 8192
+
+	.section ".stack", "aw", @nobits
+	.balign STACK_ALIGN
+	.globl _stack
+_stack:
+	.space STACK_SIZE
+	.globl _estack
+_estack:

src/arch/riscv/core/zkr.c

@@ -31,6 +31,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <errno.h>
 #include <ipxe/hart.h>
+#include <ipxe/csr.h>
 #include <ipxe/entropy.h>
 #include <ipxe/drbg.h>
 
@@ -60,6 +61,12 @@ static int zkr_entropy_enable ( void ) {
 		return rc;
 	}
 
+	/* Check if seed CSR is accessible in S-mode */
+	if ( ! csr_can_write ( "seed", 0 ) ) {
+		DBGC ( colour, "ZKR cannot access seed CSR\n" );
+		return -ENOTSUP;
+	}
+
 	/* RISC-V ISA mandates that 128 bits of full entropy shall be
 	 * obtained from 256 entropy bits read from the seed CSR.
 	 *

src/arch/riscv/include/bits/umalloc.h

@@ -0,0 +1,14 @@
+#ifndef _BITS_UMALLOC_H
+#define _BITS_UMALLOC_H
+
+/** @file
+ *
+ * RISCV-specific user memory allocation API implementations
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/sbi_umalloc.h>
+
+#endif /* _BITS_UMALLOC_H */

src/arch/riscv/include/ipxe/csr.h

@@ -0,0 +1,75 @@
+#ifndef _IPXE_CSR_H
+#define _IPXE_CSR_H
+
+/** @file
+ *
+ * Control and status registers (CSRs)
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/**
+ * Check if CSR can be read
+ *
+ * @v name		CSR name
+ * @v allowed		CSR can be read
+ */
+#define csr_can_read( name ) ( {					\
+	unsigned long stvec_orig;					\
+	unsigned long stvec_temp;					\
+	unsigned long csr;						\
+	int allowed = 0;						\
+									\
+	__asm__ __volatile__ ( /* Set temporary trap vector */		\
+			       "la %3, 1f\n\t"				\
+			       "csrrw %2, stvec, %3\n\t"		\
+			       /* Try reading CSR */			\
+			       "csrr %1, " name "\n\t"			\
+			       /* Mark as allowed if not trapped */	\
+			       "addi %0, %0, 1\n\t"			\
+			       /* Temporary trap vector */		\
+			       ".balign 4\n\t"				\
+			       "\n1:\n\t"				\
+			       /* Restore original trap vector */	\
+			       "csrw stvec, %2\n\t"			\
+			       : "+r" ( allowed ),			\
+				 "=r" ( csr ),				\
+				 "=r" ( stvec_orig ),			\
+				 "=r" ( stvec_temp ) );			\
+	allowed;							\
+	} )
+
+/**
+ * Check if CSR can be written
+ *
+ * @v name		CSR name
+ * @v value		Value to write
+ * @v allowed		CSR can be written
+ */
+#define csr_can_write( name, value ) ( {				\
+	unsigned long stvec_orig;					\
+	unsigned long stvec_temp;					\
+	unsigned long csr = (value);					\
+	int allowed = 0;						\
+									\
+	__asm__ __volatile__ ( /* Set temporary trap vector */		\
+			       "la %3, 1f\n\t"				\
+			       "csrrw %2, stvec, %3\n\t"		\
+			       /* Try writing CSR */			\
+			       "csrrw %1, " name ", %1\n\t"		\
+			       /* Mark as allowed if not trapped */	\
+			       "addi %0, %0, 1\n\t"			\
+			       /* Temporary trap vector */		\
+			       ".balign 4\n\t"				\
+			       "\n1:\n\t"				\
+			       /* Restore original trap vector */	\
+			       "csrw stvec, %2\n\t"			\
+			       : "+r" ( allowed ),			\
+				 "+r" ( csr ),				\
+				 "=r" ( stvec_orig ),			\
+				 "=r" ( stvec_temp ) );			\
+	allowed;							\
+	} )
+
+#endif /* _IPXE_CSR_H */

src/arch/riscv/include/ipxe/errno/sbi.h

@@ -0,0 +1,19 @@
+#ifndef _IPXE_ERRNO_SBI_H
+#define _IPXE_ERRNO_SBI_H
+
+/**
+ * @file
+ *
+ * RISC-V SBI platform error codes
+ *
+ * We never need to return SBI error codes ourselves, so we
+ * arbitrarily choose to use the Linux error codes as platform error
+ * codes.
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/errno/linux.h>
+
+#endif /* _IPXE_ERRNO_SBI_H */

src/arch/riscv/include/ipxe/sbi_umalloc.h

@@ -0,0 +1,18 @@
+#ifndef _IPXE_SBI_UMALLOC_H
+#define _IPXE_SBI_UMALLOC_H
+
+/** @file
+ *
+ * External memory allocation
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#ifdef UMALLOC_SBI
+#define UMALLOC_PREFIX_sbi
+#else
+#define UMALLOC_PREFIX_sbi __sbi_
+#endif
+
+#endif /* _IPXE_SBI_UMALLOC_H */

src/arch/riscv/interface/sbi/sbi_umalloc.c

@@ -0,0 +1,54 @@
+/*
+ * 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 );
+
+#include <stdlib.h>
+#include <ipxe/umalloc.h>
+
+/** @file
+ *
+ * iPXE user memory allocation API for SBI
+ *
+ */
+
+/** Equivalent of NOWHERE for user pointers */
+#define UNOWHERE ( ~UNULL )
+
+/**
+ * Reallocate external memory
+ *
+ * @v old_ptr		Memory previously allocated by umalloc(), or UNULL
+ * @v new_size		Requested size
+ * @ret new_ptr		Allocated memory, or UNULL
+ *
+ * Calling realloc() with a new size of zero is a valid way to free a
+ * memory block.
+ */
+static userptr_t sbi_urealloc ( userptr_t old_ptr, size_t new_size ) {
+
+	/* External allocation not yet implemented: allocate from heap */
+	return ( ( userptr_t ) realloc ( ( ( void * ) old_ptr ), new_size ) );
+}
+
+PROVIDE_UMALLOC ( sbi, urealloc, sbi_urealloc );

src/arch/riscv/prefix/sbiprefix.S

@@ -0,0 +1,156 @@
+/*
+ * 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
+
+/* SBI debug console extension */
+#define SBI_DBCN ( ( 'D' << 24 ) | ( 'B' << 16 ) | ( 'C' << 8 ) | 'N' )
+#define SBI_DBCN_WRITE 0x00
+
+/* SBI system reset extension */
+#define SBI_SRST ( ( 'S' << 24 ) | ( 'R' << 16 ) | ( 'S' << 8 ) | 'T' )
+#define SBI_SRST_SYSTEM_RESET 0x00
+#define SBI_RESET_COLD 0x00000001
+
+/* Relative relocation type */
+#define R_RISCV_RELATIVE 3
+
+	/* Layout of a relocation record */
+	.struct 0
+rela_offset:	.space ( __riscv_xlen / 8 )
+rela_type:	.space ( __riscv_xlen / 8 )
+rela_addend:	.space ( __riscv_xlen / 8 )
+rela_len:
+	.previous
+
+	/*
+	 * Display progress message via debug console
+	 */
+	.macro	progress message
+#ifndef NDEBUG
+	.section ".prefix.data", "aw", @progbits
+progress_\@:
+	.ascii	"\message"
+	.equ	progress_\@_len, . - progress_\@
+	.size	progress_\@, . - progress_\@
+	.previous
+	li	a7, SBI_DBCN
+	li	a6, SBI_DBCN_WRITE
+	li	a0, progress_\@_len
+	la	a1, progress_\@
+	mv	a2, zero
+	ecall
+#endif
+	.endm
+
+	/*
+	 * SBI entry point
+	 */
+	.section ".prefix", "ax", @progbits
+	.org 0
+	.globl	_sbi_start
+_sbi_start:
+	/* Preserve arguments */
+	mv	s0, a0
+	mv	s1, a1
+	progress "\nSBI->iPXE"
+
+	/* Apply dynamic relocations */
+	la	t0, _reloc
+	la	t1, _ereloc
+	la	t2, _sbi_start
+1:	/* Read relocation record */
+	LOADN	t3, rela_offset(t0)
+	LOADN	t4, rela_type(t0)
+	LOADN	t5, rela_addend(t0)
+	/* Check relocation type */
+	addi	t4, t4, -R_RISCV_RELATIVE
+	bnez	t4, 2f
+	/* Apply relocation */
+	add	t3, t3, t2
+	add	t5, t5, t2
+	STOREN	t5, (t3)
+2:	/* Loop */
+	addi	t0, t0, rela_len
+	blt	t0, t1, 1b
+	progress " .reloc"
+
+	/* Zero the bss */
+	la	t0, _bss
+	la	t1, _ebss
+1:	STOREN	zero, (t0)
+	addi	t0, t0, ( __riscv_xlen / 8 )
+	blt	t0, t1, 1b
+	progress " .bss"
+
+	/* Set up stack */
+	la	sp, _estack
+	progress " .stack"
+
+	/* Store boot hart */
+	la	t0, boot_hart
+	STOREN	s0, (t0)
+
+	/* Register device tree */
+	mv	a0, s1
+	call	register_fdt
+
+	/* Call main program */
+	progress "\n\n"
+	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.
+	 */
+	progress "\niPXE->SBI reset\n"
+	li	a7, SBI_SRST
+	li	a6, SBI_SRST_SYSTEM_RESET
+	li	a0, SBI_RESET_COLD
+	mv	a1, zero
+	ecall
+
+	/* If reset failed, lock the system */
+	progress "(reset failed)\n"
+1:	wfi
+	j	1b
+	.size	_sbi_start, . - _sbi_start
+
+	/* File split information for the compressor */
+	.section ".zinfo", "a", @progbits
+	.ascii	"COPY"
+	.word	0
+	.word	_sbi_filesz
+	.word	1

src/arch/riscv/scripts/sbi.lds

@@ -0,0 +1,119 @@
+/*
+ * Linker script for RISC-V SBI images
+ *
+ */
+
+SECTIONS {
+
+    /* Start at virtual address zero */
+    . = 0;
+
+    /* Weak symbols that need zero values if not otherwise defined */
+    .weak 0x0 : {
+	_weak = .;
+	*(.weak)
+	*(.weak.*)
+	_eweak = .;
+    }
+    _assert = ASSERT ( ( _weak == _eweak ), ".weak is non-zero length" );
+
+    /* Prefix code */
+    .prefix : {
+        _prefix = .;
+	*(.prefix)
+	*(.prefix.*)
+	_eprefix = .;
+    }
+
+    /* Program code */
+    .text : {
+	_text = .;
+	*(.text)
+	*(.text.*)
+	_etext = .;
+    }
+
+    /* Align to page size to allow linker to generate W^X segments */
+    . = ALIGN ( 4096 );
+
+    /* Read-only data */
+    .rodata : {
+	_rodata = .;
+	*(.rodata)
+	*(.rodata.*)
+	_erodata = .;
+    }
+
+    /* Writable data */
+    .data : {
+	_data = .;
+	*(.data)
+	*(.data.*)
+	KEEP(*(SORT(.tbl.*)))	/* Various tables.  See include/tables.h */
+	KEEP(*(.provided))
+	KEEP(*(.provided.*))
+	_edata = .;
+    }
+
+    /* Uninitialised and discardable data */
+    OVERLAY : {
+
+	/* Runtime relocations (discarded after use) */
+	.rela.dyn {
+	    _reloc = .;
+	    *(.rela)
+	    *(.rela.dyn)
+	}
+
+	/* Compressor information block */
+	.zinfo {
+	    _zinfo = .;
+	    KEEP(*(.zinfo))
+	    KEEP(*(.zinfo.*))
+	    _ezinfo = .;
+	}
+
+	/* Uninitialised data */
+	.bss {
+	    _bss = .;
+	    *(.bss)
+	    *(.bss.*)
+	    *(COMMON)
+	    *(.stack)
+	    *(.stack.*)
+	    /* Align to allow for easy zeroing by prefix code */
+	    . = ALIGN ( 16 );
+	    _ebss = .;
+	}
+    }
+
+    /* Calculate end of relocations
+     *
+     * This cannot be done by placing "_ereloc = .;" inside the
+     * .rela.dyn section, since the dynamic relocations are not
+     * present in the input sections but are instead generated during
+     * linking.
+     */
+    _ereloc = ( _reloc + __load_stop_reladyn - __load_start_reladyn );
+
+    /* Length of initialised data */
+    _sbi_filesz = ABSOLUTE ( _ereloc );
+
+    /* Unwanted sections */
+    /DISCARD/ : {
+	*(.comment)
+	*(.comment.*)
+	*(.note)
+	*(.note.*)
+	*(.eh_frame)
+	*(.eh_frame.*)
+	*(.dynamic)
+	*(.dynsym)
+	*(.dynstr)
+	*(.einfo)
+	*(.einfo.*)
+	*(.discard)
+	*(.discard.*)
+	*(.pci_devlist.*)
+    }
+}

src/arch/riscv32/Makefile.sbi

@@ -0,0 +1,6 @@
+# -*- makefile -*- : Force emacs to use Makefile mode
+
+# Include generic SBI Makefile
+#
+MAKEDEPS	+= arch/riscv/Makefile.sbi
+include arch/riscv/Makefile.sbi

src/arch/riscv32/include/ipxe/sbi/dhcparch.h

@@ -0,0 +1,20 @@
+#ifndef _IPXE_SBI_DHCPARCH_H
+#define _IPXE_SBI_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_RISCV32
+
+/** DHCP client network device interface */
+#define DHCP_ARCH_CLIENT_NDI 1 /* UNDI */ , 3, 10 /* v3.10 */
+
+#endif /* _IPXE_SBI_DHCPARCH_H */

src/arch/riscv64/Makefile.sbi

@@ -0,0 +1,6 @@
+# -*- makefile -*- : Force emacs to use Makefile mode
+
+# Include generic SBI Makefile
+#
+MAKEDEPS	+= arch/riscv/Makefile.sbi
+include arch/riscv/Makefile.sbi

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

@@ -0,0 +1,20 @@
+#ifndef _IPXE_SBI_DHCPARCH_H
+#define _IPXE_SBI_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_SBI_DHCPARCH_H */

src/config/defaults/sbi.h

@@ -0,0 +1,36 @@
+#ifndef CONFIG_DEFAULTS_SBI_H
+#define CONFIG_DEFAULTS_SBI_H
+
+/** @file
+ *
+ * Configuration defaults for RISC-V SBI
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#define IOAPI_RISCV
+#define IOMAP_VIRT
+#define DMAAPI_FLAT
+#define UACCESS_FLAT
+#define TIMER_ZICNTR
+#define ENTROPY_ZKR
+
+#define CONSOLE_SBI
+#define REBOOT_SBI
+#define UMALLOC_SBI
+
+#define ACPI_NULL
+#define MPAPI_NULL
+#define NAP_NULL
+#define PCIAPI_NULL
+#define SANBOOT_NULL
+#define SMBIOS_NULL
+#define TIME_NULL
+
+#define IMAGE_SCRIPT
+
+#define REBOOT_CMD
+#define POWEROFF_CMD
+
+#endif /* CONFIG_DEFAULTS_SBI_H */