util: add rmodtool for parsing ELF files to rmodules

The current implementation of creating rmodules relies
on invoking the linker in a certain manner with the
relocations overlaid on the BSS section. It's not really
surprising that the linker doesn't always behave the way
one wants depending on the linker used and the architecture.
Instead, introduce rmodtool which takes an ELF file as an
input, parses it, and creates a new ELF file in the format
the rmodule loader expects.

Change-Id: I31ac2d327d450ef841c3a7d9740b787278382bef
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5378
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

5 files changed, 800 insertions, 16 deletions

diff --git a/util/cbfstool/Makefile b/util/cbfstool/Makefile
index bc49c64002..e647c88062 100644
--- a/util/cbfstool/Makefile
+++ b/util/cbfstool/Makefile
@@ -8,30 +8,40 @@ CFLAGS += -Wstrict-aliasing -Werror
 CFLAGS += -Wshadow
 LDFLAGS += -g
 
-BINARY:=$(obj)/cbfstool
+CBFSTOOL_BINARY:=$(obj)/cbfstool
 
-COMMON:=cbfstool.o common.o cbfs_image.o compress.o fit.o
-COMMON+=elfheaders.o cbfs-mkstage.o cbfs-mkpayload.o xdr.o
+CBFSTOOL_COMMON:=cbfstool.o common.o cbfs_image.o compress.o fit.o
+CBFSTOOL_COMMON+=elfheaders.o cbfs-mkstage.o cbfs-mkpayload.o xdr.o
 # LZMA
-COMMON+=lzma/lzma.o
-COMMON+=lzma/C/LzFind.o  lzma/C/LzmaDec.o  lzma/C/LzmaEnc.o
+CBFSTOOL_COMMON+=lzma/lzma.o
+CBFSTOOL_COMMON+=lzma/C/LzFind.o  lzma/C/LzmaDec.o  lzma/C/LzmaEnc.o
 
-COMMON+=linux_trampoline.o cbfs-payload-linux.o
+CBFSTOOL_COMMON+=linux_trampoline.o cbfs-payload-linux.o
 
-COMMON:=$(addprefix $(obj)/,$(COMMON))
+CBFSTOOL_COMMON:=$(addprefix $(obj)/,$(CBFSTOOL_COMMON))
 
-all: dep $(BINARY)
+
+RMODTOOL_BINARY:=$(obj)/rmodtool
+RMODTOOL_COMMON:=rmodtool.o rmodule.o common.o elfheaders.o xdr.o
+
+RMODTOOL_COMMON:=$(addprefix $(obj)/,$(RMODTOOL_COMMON))
+
+all: dep $(CBFSTOOL_BINARY) $(RMODTOOL_BINARY)
 
 $(obj)/%.o: %.c
 	$(HOSTCC) $(CFLAGS) -c -o $@ $<
 
 clean:
-	rm -f $(COMMON) $(BINARY)
+	rm -f $(CBFSTOOL_COMMON) $(CBFSTOOL_BINARY)
+	rm -f $(RMODTOOL_COMMON) $(RMODTOOL_BINARY)
 
 tags:
 	ctags *.[ch]
 
-$(obj)/cbfstool:$(COMMON)
+$(obj)/cbfstool:$(CBFSTOOL_COMMON)
+	$(HOSTCC) $(CFLAGS) -o $@ $^
+
+$(obj)/rmodtool:$(RMODTOOL_COMMON)
 	$(HOSTCC) $(CFLAGS) -o $@ $^
 
 dep:
diff --git a/util/cbfstool/Makefile.inc b/util/cbfstool/Makefile.inc
index c19b7d9070..2923938ab7 100644
--- a/util/cbfstool/Makefile.inc
+++ b/util/cbfstool/Makefile.inc
@@ -17,10 +17,16 @@ cbfsobj += LzmaEnc.o
 cbfsobj += linux_trampoline.o
 cbfsobj += cbfs-payload-linux.o
 
-CBFSTOOLFLAGS= -g
+rmodobj += rmodtool.o
+rmodobj += rmodule.o
+rmodobj += common.o
+rmodobj += elfheaders.o
+rmodobj += xdr.o
+
+TOOLFLAGS= -g
 
 ifeq ($(shell uname -s | cut -c-7 2>/dev/null), MINGW32)
-CBFSTOOLFLAGS+=-mno-ms-bitfields
+TOOLFLAGS+=-mno-ms-bitfields
 endif
 
 $(objutil)/cbfstool:
@@ -28,17 +34,21 @@ $(objutil)/cbfstool:
 
 $(objutil)/cbfstool/%.o: $(top)/util/cbfstool/%.c
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@))\n"
-	$(HOSTCC) $(CBFSTOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
+	$(HOSTCC) $(TOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
 
 $(objutil)/cbfstool/%.o: $(top)/util/cbfstool/lzma/%.c
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@))\n"
-	$(HOSTCC) $(CBFSTOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
+	$(HOSTCC) $(TOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
 
 $(objutil)/cbfstool/%.o: $(top)/util/cbfstool/lzma/C/%.c
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@))\n"
-	$(HOSTCC) $(CBFSTOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
+	$(HOSTCC) $(TOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
 
 $(objutil)/cbfstool/cbfstool: $(objutil)/cbfstool $(addprefix $(objutil)/cbfstool/,$(cbfsobj))
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@)) (link)\n"
-	$(HOSTCC) $(CBFSTOOLFLAGS) -o $@ $(addprefix $(objutil)/cbfstool/,$(cbfsobj))
+	$(HOSTCC) $(TOOLFLAGS) -o $@ $(addprefix $(objutil)/cbfstool/,$(cbfsobj))
+
+$(objutil)/cbfstool/rmodtool: $(objutil)/cbfstool $(addprefix $(objutil)/cbfstool/,$(rmodobj))
+	printf "    HOSTCC     $(subst $(objutil)/,,$(@)) (link)\n"
+	$(HOSTCC) $(TOOLFLAGS) -o $@ $(addprefix $(objutil)/cbfstool/,$(rmodobj))
 
diff --git a/util/cbfstool/rmodtool.c b/util/cbfstool/rmodtool.c
new file mode 100644
index 0000000000..1455cd9a3b
--- /dev/null
+++ b/util/cbfstool/rmodtool.c
@@ -0,0 +1,106 @@
+/*
+ * cbfstool, CLI utility for creating rmodules
+ *
+ * Copyright (C) 2014 Google, Inc.
+ *
+ * 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; version 2 of the License.
+ *
+ * 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 St, Fifth Floor, Boston, MA, 02110-1301 USA
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <getopt.h>
+#include "common.h"
+#include "rmodule.h"
+
+static const char *optstring  = "i:o:vh?";
+static struct option long_options[] = {
+	{"inelf",        required_argument, 0, 'i' },
+	{"outelf",       required_argument, 0, 'o' },
+	{"verbose",      no_argument,       0, 'v' },
+	{"help",         no_argument,       0, 'h' },
+	{NULL,           0,                 0,  0  }
+};
+
+static void usage(char *name)
+{
+	printf(
+		"rmodtool: utility for creating rmodules\n\n"
+		"USAGE: %s [-h] [-v] <-i|--inelf name> <-o|--outelf name>\n",
+		name
+	);
+}
+
+int main(int argc, char *argv[])
+{
+	int c;
+	struct buffer elfin;
+	struct buffer elfout;
+	const char *input_file = NULL;
+	const char *output_file = NULL;
+
+	if (argc < 3) {
+		usage(argv[0]);
+		return 1;
+	}
+
+	while (1) {
+		int optindex = 0;
+
+		c = getopt_long(argc, argv, optstring, long_options, &optindex);
+
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'i':
+			input_file = optarg;
+			break;
+		case 'h':
+			usage(argv[0]);
+			return 1;
+		case 'o':
+			output_file = optarg;
+			break;
+		case 'v':
+			verbose++;
+			break;
+		default:
+			break;
+		}
+	}
+
+	if (input_file == NULL || output_file == NULL) {
+		usage(argv[0]);
+		return 1;
+	}
+
+	if (buffer_from_file(&elfin, input_file)) {
+		ERROR("Couldn't read in file '%s'.\n", input_file);
+		return 1;
+	}
+
+	if (rmodule_create(&elfin, &elfout)) {
+		ERROR("Unable to create rmodule from '%s'.\n", input_file);
+		return 1;
+	}
+
+	if (buffer_write_file(&elfout, output_file)) {
+		ERROR("Unable to write rmodule elf '%s'.\n", output_file);
+		return 1;
+	}
+
+	return 0;
+}
diff --git a/util/cbfstool/rmodule.c b/util/cbfstool/rmodule.c
new file mode 100644
index 0000000000..a5730f12ba
--- /dev/null
+++ b/util/cbfstool/rmodule.c
@@ -0,0 +1,628 @@
+/*
+ ;* Copyright (C) 2014 Google, Inc.
+ *
+ * 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; version 2 of the License.
+ *
+ * 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 St, Fifth Floor, Boston, MA, 02110-1301 USA
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "elfparsing.h"
+#include "rmodule.h"
+#include "../../src/include/rmodule-defs.h"
+
+struct rmod_context;
+
+struct arch_ops {
+	int arch;
+	/* Determine if relocation is a valid type for the architecture. */
+	int (*valid_type)(struct rmod_context *ctx, Elf64_Rela *rel);
+	/* Determine if relocation should be emitted. */
+	int (*should_emit)(struct rmod_context *ctx, Elf64_Rela *rel);
+};
+
+struct rmod_context {
+	/* Ops to process relocations. */
+	struct arch_ops *ops;
+
+	/* endian conversion ops */
+	struct xdr *xdr;
+
+	/* Parsed ELF sturcture. */
+	struct parsed_elf pelf;
+	/* Program segment. */
+	Elf64_Phdr *phdr;
+
+	/* Collection of relocation addresses fixup in the module. */
+	Elf64_Xword nrelocs;
+	Elf64_Addr *emitted_relocs;
+
+	/* The following fields are addresses within the linked program. */
+	Elf64_Addr link_addr;
+	Elf64_Addr entry;
+	Elf64_Addr parameters_begin;
+	Elf64_Addr parameters_end;
+	Elf64_Addr bss_begin;
+	Elf64_Addr bss_end;
+	Elf64_Xword size;
+};
+
+/*
+ * Architecture specific support operations.
+ */
+static int valid_reloc_386(struct rmod_context *ctx, Elf64_Rela *rel)
+{
+	int type;
+
+	type = ELF64_R_TYPE(rel->r_info);
+
+	/* Only these 2 relocations are expected to be found. */
+	return (type == R_386_32 || type == R_386_PC32);
+}
+
+static int should_emit_386(struct rmod_context *ctx, Elf64_Rela *rel)
+{
+	int type;
+
+	type = ELF64_R_TYPE(rel->r_info);
+
+	/* R_386_32 relocations are absolute. Must emit these. */
+	return (type == R_386_32);
+}
+
+static struct arch_ops reloc_ops[] = {
+	{
+		.arch = EM_386,
+		.valid_type = valid_reloc_386,
+		.should_emit = should_emit_386,
+	},
+};
+
+/*
+ * Relocation processing loops.
+ */
+
+static int for_each_reloc(struct rmod_context *ctx, int do_emit)
+{
+	Elf64_Half i;
+	struct parsed_elf *pelf = &ctx->pelf;
+
+	for (i = 0; i < pelf->ehdr.e_shnum; i++) {
+		Elf64_Shdr *shdr;
+		Elf64_Rela *relocs;
+		Elf64_Xword nrelocs;
+		Elf64_Xword j;
+
+		relocs = pelf->relocs[i];
+
+		/* No relocations in this section. */
+		if (relocs == NULL)
+			continue;
+
+		shdr = &pelf->shdr[i];
+		nrelocs = shdr->sh_size / shdr->sh_entsize;
+
+		for (j = 0; j < nrelocs; j++) {
+			Elf64_Rela *r = &relocs[j];
+
+			if (!ctx->ops->valid_type(ctx, r)) {
+				ERROR("Invalid reloc type: %u\n",
+				      (unsigned int)ELF64_R_TYPE(r->r_info));
+				return -1;
+			}
+
+			if (ctx->ops->should_emit(ctx, r)) {
+				int n = ctx->nrelocs;
+				if (do_emit)
+					ctx->emitted_relocs[n] = r->r_offset;
+				ctx->nrelocs++;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static int find_program_segment(struct rmod_context *ctx)
+{
+	int i;
+	int nsegments;
+	struct parsed_elf *pelf;
+	Elf64_Phdr *phdr;
+
+	pelf = &ctx->pelf;
+
+	/* There should only be a single loadable segment. */
+	nsegments = 0;
+	for (i = 0; i < pelf->ehdr.e_phnum; i++) {
+		if (pelf->phdr[i].p_type != PT_LOAD)
+			continue;
+		phdr = &pelf->phdr[i];
+		nsegments++;
+	}
+
+	if (nsegments != 1) {
+		ERROR("Unexepcted number of loadable segments: %d.\n",
+		      nsegments);
+		return -1;
+	}
+
+	INFO("Segment at 0x%0llx, file size 0x%0llx, mem size 0x%0llx.\n",
+	     (long long)phdr->p_vaddr, (long long)phdr->p_filesz,
+	     (long long)phdr->p_memsz);
+
+	ctx->phdr = phdr;
+
+	return 0;
+}
+
+static int
+filter_relocation_sections(struct rmod_context *ctx)
+{
+	int i;
+	const char *shstrtab;
+	struct parsed_elf *pelf;
+	const Elf64_Phdr *phdr;
+
+	pelf = &ctx->pelf;
+	phdr = ctx->phdr;
+	shstrtab = buffer_get(pelf->strtabs[pelf->ehdr.e_shstrndx]);
+
+	/*
+	 * Find all relocation sections that contain relocation entries
+	 * for sections that fall within the bounds of the segment. For
+	 * easier processing the pointer to the relocation array for the
+	 * sections that don't fall within the loadable program are NULL'd
+	 * out.
+	 */
+	for (i = 0; i < pelf->ehdr.e_shnum; i++) {
+		Elf64_Shdr *shdr;
+		Elf64_Word sh_info;
+		const char *section_name;
+
+		shdr = &pelf->shdr[i];
+
+		/* Ignore non-relocation sections. */
+		if (shdr->sh_type != SHT_RELA && shdr->sh_type != SHT_REL)
+			continue;
+
+		/* Obtain section which relocations apply. */
+		sh_info = shdr->sh_info;
+		shdr = &pelf->shdr[sh_info];
+
+		section_name = &shstrtab[shdr->sh_name];
+		DEBUG("Relocation section found for '%s' section.\n",
+		      section_name);
+
+		/* Do not process relocations for debug sections. */
+		if (strstr(section_name, ".debug") != NULL) {
+			pelf->relocs[i] = NULL;
+			continue;
+		}
+
+		/*
+		 * If relocations apply to a non program section ignore the
+		 * relocations for future processing.
+		 */
+		if (shdr->sh_type != SHT_PROGBITS) {
+			pelf->relocs[i] = NULL;
+			continue;
+		}
+
+		if (shdr->sh_addr < phdr->p_vaddr ||
+		    ((shdr->sh_addr + shdr->sh_size) >
+		     (phdr->p_vaddr + phdr->p_memsz))) {
+			ERROR("Relocations being applied to section %d not "
+			      "within segment region.\n", sh_info);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+static int vaddr_cmp(const void *a, const void *b)
+{
+	const Elf64_Addr *pa = a;
+	const Elf64_Addr *pb = b;
+
+	if (*pa < *pb)
+		return -1;
+	if (*pa > *pb)
+		return 1;
+	return 0;
+}
+
+static int collect_relocations(struct rmod_context *ctx)
+{
+	int nrelocs;
+
+	/*
+	 * The relocs array in the pelf should only contain relocations that
+	 * apply to the program. Count the number relocations. Then collect
+	 * them into the allocated buffer.
+	 */
+	if (for_each_reloc(ctx, 0))
+		return -1;
+
+	nrelocs = ctx->nrelocs;
+	INFO("%d relocations to be emitted.\n", nrelocs);
+	if (!nrelocs) {
+		ERROR("No valid relocations in file.\n");
+		return -1;
+	}
+
+	/* Reset the counter for indexing into the array. */
+	ctx->nrelocs = 0;
+	ctx->emitted_relocs = calloc(nrelocs, sizeof(Elf64_Addr));
+	/* Write out the relocations into the emitted_relocs array. */
+	if (for_each_reloc(ctx, 1))
+		return -1;
+
+	if (ctx->nrelocs != nrelocs) {
+		ERROR("Mismatch counted and emitted relocations: %zu vs %zu.\n",
+		      (size_t)nrelocs, (size_t)ctx->nrelocs);
+		return -1;
+	}
+
+	/* Sort the relocations by their address. */
+	qsort(ctx->emitted_relocs, nrelocs, sizeof(Elf64_Addr), vaddr_cmp);
+
+	return 0;
+}
+
+static int
+populate_sym(struct rmod_context *ctx, const char *sym_name, Elf64_Addr *addr,
+             int nsyms, const char *strtab)
+{
+	int i;
+	Elf64_Sym *syms;
+
+	syms = ctx->pelf.syms;
+
+	for (i = 0; i < nsyms; i++) {
+		if (syms[i].st_name == 0)
+			continue;
+		if (strcmp(sym_name, &strtab[syms[i].st_name]))
+			continue;
+		DEBUG("%s -> 0x%llx\n", sym_name, (long long)syms[i].st_value);
+		*addr = syms[i].st_value;
+		return 0;
+	}
+	ERROR("symbol '%s' not found.\n", sym_name);
+	return -1;
+}
+
+static int populate_program_info(struct rmod_context *ctx)
+{
+	int i;
+	const char *strtab;
+	struct parsed_elf *pelf;
+	Elf64_Ehdr *ehdr;
+	int nsyms;
+
+	pelf = &ctx->pelf;
+	ehdr = &pelf->ehdr;
+
+	/* Obtain the string table. */
+	strtab = NULL;
+	for (i = 0; i < ehdr->e_shnum; i++) {
+		if (ctx->pelf.strtabs[i] == NULL)
+			continue;
+		/* Don't use the section headers' string table. */
+		if (i == ehdr->e_shstrndx)
+			continue;
+		strtab = buffer_get(ctx->pelf.strtabs[i]);
+		break;
+	}
+
+	if (strtab == NULL) {
+		ERROR("No string table found.\n");
+		return -1;
+	}
+
+	/* Determine number of symbols. */
+	nsyms = 0;
+	for (i = 0; i < ehdr->e_shnum; i++) {
+		if (pelf->shdr[i].sh_type != SHT_SYMTAB)
+			continue;
+
+		nsyms = pelf->shdr[i].sh_size / pelf->shdr[i].sh_entsize;
+		break;
+	}
+
+	if (populate_sym(ctx, "_module_params_begin", &ctx->parameters_begin,
+	                 nsyms, strtab))
+		return -1;
+
+	if (populate_sym(ctx, "_module_params_end", &ctx->parameters_end,
+	                 nsyms, strtab))
+		return -1;
+
+	if (populate_sym(ctx, "_bss", &ctx->bss_begin, nsyms, strtab))
+		return -1;
+
+	if (populate_sym(ctx, "_ebss", &ctx->bss_end, nsyms, strtab))
+		return -1;
+
+	if (populate_sym(ctx, "__rmodule_entry", &ctx->entry, nsyms, strtab))
+		return -1;
+
+	/* Link address is the virtual address of the program segment. */
+	ctx->link_addr = ctx->phdr->p_vaddr;
+
+	/* The program size is the memsz of the program segment. */
+	ctx->size = ctx->phdr->p_memsz;
+
+	return 0;
+}
+
+static int
+add_section(struct elf_writer *ew, struct buffer *data, const char *name,
+            Elf64_Addr addr, Elf64_Word size)
+{
+	Elf64_Shdr shdr;
+	int ret;
+
+	memset(&shdr, 0, sizeof(shdr));
+	if (data != NULL) {
+		shdr.sh_type = SHT_PROGBITS;
+		shdr.sh_flags = SHF_ALLOC | SHF_WRITE | SHF_EXECINSTR;
+	} else {
+		shdr.sh_type = SHT_NOBITS;
+		shdr.sh_flags = SHF_ALLOC;
+	}
+	shdr.sh_addr = addr;
+	shdr.sh_offset = addr;
+	shdr.sh_size = size;
+
+	ret = elf_writer_add_section(ew, &shdr, data, name);
+
+	if (ret)
+		ERROR("Could not add '%s' section.\n", name);
+
+	return ret;
+}
+
+static int
+write_elf(const struct rmod_context *ctx, const struct buffer *in,
+          struct buffer *out)
+{
+	int i;
+	int ret;
+	int bit64;
+	size_t loc;
+	size_t rmod_data_size;
+	struct elf_writer *ew;
+	struct buffer rmod_data;
+	struct buffer rmod_header;
+	struct buffer program;
+	struct buffer relocs;
+	Elf64_Xword total_size;
+	Elf64_Addr addr;
+	Elf64_Ehdr ehdr;
+
+	bit64 = ctx->pelf.ehdr.e_ident[EI_CLASS] == ELFCLASS64;
+
+	/*
+	 * 3 sections will be added  to the ELF file.
+	 * +------------------+
+	 * |  rmodule header  |
+	 * +------------------+
+	 * |     program      |
+	 * +------------------+
+	 * |   relocations    |
+	 * +------------------+
+	 */
+
+	/* Create buffer for header and relocations. */
+	rmod_data_size = sizeof(struct rmodule_header);
+	if (bit64)
+		rmod_data_size += ctx->nrelocs * sizeof(Elf64_Addr);
+	else
+		rmod_data_size += ctx->nrelocs * sizeof(Elf32_Addr);
+
+	if (buffer_create(&rmod_data, rmod_data_size, "rmod"))
+		return -1;
+
+	buffer_splice(&rmod_header, &rmod_data,
+	              0, sizeof(struct rmodule_header));
+	buffer_clone(&relocs, &rmod_data);
+	buffer_seek(&relocs, sizeof(struct rmodule_header));
+
+	/* Reset current location. */
+	buffer_set_size(&rmod_header, 0);
+	buffer_set_size(&relocs, 0);
+
+	/* Program contents. */
+	buffer_splice(&program, in, ctx->phdr->p_offset, ctx->phdr->p_filesz);
+
+	/* Create ELF writer with modified entry point. */
+	memcpy(&ehdr, &ctx->pelf.ehdr, sizeof(ehdr));
+	ehdr.e_entry = ctx->entry;
+	ew = elf_writer_init(&ehdr);
+
+	if (ew == NULL) {
+		ERROR("Failed to create ELF writer.\n");
+		buffer_delete(&rmod_data);
+		return -1;
+	}
+
+	/* Write out rmodule_header. */
+	ctx->xdr->put16(&rmod_header, RMODULE_MAGIC);
+	ctx->xdr->put8(&rmod_header, RMODULE_VERSION_1);
+	ctx->xdr->put8(&rmod_header, 0);
+	/* payload_begin_offset */
+	loc = sizeof(struct rmodule_header);
+	ctx->xdr->put32(&rmod_header, loc);
+	/* payload_end_offset */
+	loc += ctx->phdr->p_filesz;
+	ctx->xdr->put32(&rmod_header, loc);
+	/* relocations_begin_offset */
+	ctx->xdr->put32(&rmod_header, loc);
+	/* relocations_end_offset */
+	if (bit64)
+		loc += ctx->nrelocs * sizeof(Elf64_Addr);
+	else
+		loc += ctx->nrelocs * sizeof(Elf32_Addr);
+	ctx->xdr->put32(&rmod_header, loc);
+	/* module_link_start_address */
+	ctx->xdr->put32(&rmod_header, ctx->link_addr);
+	/* module_program_size */
+	ctx->xdr->put32(&rmod_header, ctx->size);
+	/* module_entry_point */
+	ctx->xdr->put32(&rmod_header, ctx->entry);
+	/* parameters_begin */
+	ctx->xdr->put32(&rmod_header, ctx->parameters_begin);
+	/* parameters_end */
+	ctx->xdr->put32(&rmod_header, ctx->parameters_end);
+	/* bss_begin */
+	ctx->xdr->put32(&rmod_header, ctx->bss_begin);
+	/* bss_end */
+	ctx->xdr->put32(&rmod_header, ctx->bss_end);
+	/* padding[4] */
+	ctx->xdr->put32(&rmod_header, 0);
+	ctx->xdr->put32(&rmod_header, 0);
+	ctx->xdr->put32(&rmod_header, 0);
+	ctx->xdr->put32(&rmod_header, 0);
+
+	/* Write the relocations. */
+	for (i = 0; i < ctx->nrelocs; i++) {
+		if (bit64)
+			ctx->xdr->put64(&relocs, ctx->emitted_relocs[i]);
+		else
+			ctx->xdr->put32(&relocs, ctx->emitted_relocs[i]);
+	}
+
+	total_size = 0;
+	addr = 0;
+
+	/*
+	 * There are 2 cases to deal with. The program has a large NOBITS
+	 * section and the relocations can fit entirely within occupied memory
+	 * region for the program. The other is that the relocations increase
+	 * the memory footprint of the program if it was loaded directly into
+	 * the region it would run. The rmdoule header is a fixed cost that
+	 * is considered a part of the program.
+	 */
+	total_size += buffer_size(&rmod_header);
+	total_size += ctx->phdr->p_memsz;
+	if (buffer_size(&relocs) + ctx->phdr->p_filesz > total_size) {
+		total_size -= ctx->phdr->p_memsz;
+		total_size += buffer_size(&relocs);
+		total_size += ctx->phdr->p_filesz;
+	}
+
+	ret = add_section(ew, &rmod_header, ".header", addr,
+	                  buffer_size(&rmod_header));
+	if (ret < 0)
+		goto out;
+	addr += buffer_size(&rmod_header);
+
+	ret = add_section(ew, &program, ".program", addr, ctx->phdr->p_filesz);
+	if (ret < 0)
+		goto out;
+	addr += ctx->phdr->p_filesz;
+
+	ret = add_section(ew, &relocs, ".relocs", addr, buffer_size(&relocs));
+	if (ret < 0)
+		goto out;
+	addr += buffer_size(&relocs);
+
+	if (total_size != addr) {
+		ret = add_section(ew, NULL, ".empty", addr, total_size - addr);
+		if (ret < 0)
+			goto out;
+	}
+
+	/*
+	 * Ensure last section has a memory usage that meets the required
+	 * total size of the program in memory.
+	 */
+
+	ret = elf_writer_serialize(ew, out);
+	if (ret < 0)
+		ERROR("Failed to serialize ELF to buffer.\n");
+
+out:
+	buffer_delete(&rmod_data);
+	elf_writer_destroy(ew);
+
+	return ret;
+}
+
+int rmodule_create(const struct buffer *elfin, struct buffer *elfout)
+{
+	struct rmod_context ctx;
+	struct parsed_elf *pelf;
+	int i;
+	int ret;
+
+	ret = -1;
+	memset(&ctx, 0, sizeof(ctx));
+	pelf = &ctx.pelf;
+
+	if (parse_elf(elfin, pelf, ELF_PARSE_ALL)) {
+		ERROR("Couldn't parse ELF!\n");
+		return -1;
+	}
+
+	/* Only allow executables to be turned into rmodules. */
+	if (pelf->ehdr.e_type != ET_EXEC) {
+		ERROR("ELF is not an executable: %u.\n", pelf->ehdr.e_type);
+		goto out;
+	}
+
+	/* Determine if architecture is supported. */
+	for (i = 0; i < ARRAY_SIZE(reloc_ops); i++) {
+		if (reloc_ops[i].arch == pelf->ehdr.e_machine) {
+			ctx.ops = &reloc_ops[i];
+			break;
+		}
+	}
+
+	if (ctx.ops == NULL) {
+		ERROR("ELF is unsupported arch: %u.\n", pelf->ehdr.e_machine);
+		goto out;
+	}
+
+	/* Set the endian ops. */
+	if (ctx.pelf.ehdr.e_ident[EI_DATA] == ELFDATA2MSB)
+		ctx.xdr = &xdr_be;
+	else
+		ctx.xdr = &xdr_le;
+
+	if (find_program_segment(&ctx))
+		goto out;
+
+	if (filter_relocation_sections(&ctx))
+		goto out;
+
+	if (collect_relocations(&ctx))
+		goto out;
+
+	if (populate_program_info(&ctx))
+		goto out;
+
+	if (write_elf(&ctx, elfin, elfout))
+		goto out;
+
+	ret = 0;
+
+out:
+	free(ctx.emitted_relocs);
+	parsed_elf_destroy(pelf);
+	return ret;
+}
diff --git a/util/cbfstool/rmodule.h b/util/cbfstool/rmodule.h
new file mode 100644
index 0000000000..94f8f3d064
--- /dev/null
+++ b/util/cbfstool/rmodule.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2014 Google, Inc.
+ *
+ * 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; version 2 of the License.
+ *
+ * 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 St, Fifth Floor, Boston, MA, 02110-1301 USA
+ */
+
+#ifndef TOOL_RMODULE_H
+#define TOOL_RMODULE_H
+
+#include "elf.h"
+#include "common.h"
+
+/*
+ * Parse an ELF file within the elfin buffer and fill in the elfout buffer
+ * with a created rmodule in ELF format. Return 0 on success, < 0 on error.
+ */
+int rmodule_create(const struct buffer *elfin, struct buffer *elfout);
+
+#endif /* TOOL_RMODULE_H */