kexec-tools: Add vmcore-dmesg

vmcore-dmesg is a trivial utility to extract the dmesg from a vmcore.
This was written in reaction to problems I was having building
makedumpfile, and using makedumpfile for extracting dmesg.  makedumpfile
does a whole lot of things, uses a whole lot of libraries and which
make it hard to compile and a little bit clunky to remember the command
line switches.

So I have written the trivial vmcore-dmesg program that reads a vmcore
either /proc/vmcore or a saved version vmcore and writes the dmesg to stdout.

There is nothing to vmcore-dmesg and all of the arch dependencies are wrapped
up in generating the core file.  Which means a vmcore-dmesg should work with
core files of all architectures without needing a rebuild.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
[ horms@verge.net.au removed trailing white-space ]
Signed-off-by: Simon Horman <horms@verge.net.au>

3 files changed, 575 insertions, 0 deletions

diff --git a/vmcore-dmesg/Makefile b/vmcore-dmesg/Makefile
new file mode 100644
index 0000000..5a6d84a
--- /dev/null
+++ b/vmcore-dmesg/Makefile
@@ -0,0 +1,29 @@
+#
+# vmcore-dmesg (reading demsg from vmcore)
+#
+
+VMCORE_DMESG_SRCS:= vmcore-dmesg/vmcore-dmesg.c
+
+VMCORE_DMESG_OBJS = $(call objify, $(VMCORE_DMESG_SRCS))
+VMCORE_DMESG_DEPS = $(call depify, $(VMCORE_DMESG_OBJS))
+
+VMCORE_DMESG = $(SBINDIR)/vmcore-dmesg
+VMCORE_DMESG_MANPAGE = $(MANDIR)/man8/vmcore-dmesg.8
+
+dist += vmcore-dmesg/Makefile $(VMCORE_DMESG_SRCS) vmcore-dmesg/vmcore-dmesg.8
+clean += $(VMCORE_DMESG_OBJS) $(VMCORE_DMESG_DEPS) $(VMCORE_DMESG) $(VMCORE_DMESG_MANPAGE)
+
+-include $(VMCORE_DMESG_DEPS)
+
+$(VMCORE_DMESG): $(VMCORE_DMESG_OBJS)
+	@$(MKDIR) -p $(@D)
+	$(LINK.o) -o $@ $^ $(CFLAGS)
+
+$(VMCORE_DMESG_MANPAGE): vmcore-dmesg/vmcore-dmesg.8
+	$(MKDIR) -p     $(MANDIR)/man8
+	cp vmcore-dmesg/vmcore-dmesg.8 $(VMCORE_DMESG_MANPAGE)
+echo::
+	@echo "VMCORE_DMESG_SRCS $(VMCORE_DMESG_SRCS)"
+	@echo "VMCORE_DMESG_DEPS $(VMCORE_DMESG_DEPS)"
+	@echo "VMCORE_DMESG_OBJS $(VMCORE_DMESG_OBJS)"
+
diff --git a/vmcore-dmesg/vmcore-dmesg.8 b/vmcore-dmesg/vmcore-dmesg.8
new file mode 100644
index 0000000..d9e3c62
--- /dev/null
+++ b/vmcore-dmesg/vmcore-dmesg.8
@@ -0,0 +1,42 @@
+.\"                                      Hey, EMACS: -*- nroff -*-
+.\" First parameter, NAME, should be all caps
+.\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
+.\" other parameters are allowed: see man(7), man(1)
+.TH VMCORE-DMESG 8 "Sep 7, 2010"
+.\" Please adjust this date whenever revising the manpage.
+.\"
+.\" Some roff macros, for reference:
+.\" .nh        disable hyphenation
+.\" .hy        enable hyphenation
+.\" .ad l      left justify
+.\" .ad b      justify to both left and right margins
+.\" .nf        disable filling
+.\" .fi        enable filling
+.\" .br        insert line break
+.\" .sp <n>    insert n+1 empty lines
+.\" for manpage-specific macros, see man(7)
+.SH NAME
+vmcore-dmesg \- This is just a placeholder until real man page has been written
+.SH SYNOPSIS
+.B vmcore-dmesg
+.RI " vmcore"
+.SH DESCRIPTION
+.PP
+.\" TeX users may be more comfortable with the \fB<whatever>\fP and
+.\" \fI<whatever>\fP escape sequences to invode bold face and italics,
+.\" respectively.
+\fBvmcore-dmesg\fP extracts the dmesg from a vmcore and write it to
+standard out.  \fBvmcore-dmesg\fP works against either
+\fB/proc/vmcore\fP in a crash dump capture context or a copy
+of \fB/proc/vmcore\fP that has been saved for later analysis.  A
+single build of \fBvmcore-dmesg\fP should work against any linux
+vmcore written created on any architecture.
+
+.\"These programs follow the usual GNU command line syntax, with long
+.\"options starting with two dashes (`-').
+.\"A summary of options is included below.
+.\"For a complete description, see the Info files.
+.SH SEE ALSO
+kexec(8)
+.SH AUTHOR
+vmcore-dmesg was written by Eric Biederman.
diff --git a/vmcore-dmesg/vmcore-dmesg.c b/vmcore-dmesg/vmcore-dmesg.c
new file mode 100644
index 0000000..7015894
--- /dev/null
+++ b/vmcore-dmesg/vmcore-dmesg.c
@@ -0,0 +1,504 @@
+#define _XOPEN_SOURCE 600
+#define _LARGEFILE_SOURCE 1
+#define _FILE_OFFSET_BITS 64
+#include <endian.h>
+#include <byteswap.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <elf.h>
+
+/* The 32bit and 64bit note headers make it clear we don't care */
+typedef Elf32_Nhdr Elf_Nhdr;
+
+static const char *fname;
+static Elf64_Ehdr ehdr;
+static Elf64_Phdr *phdr;
+
+static char osrelease[4096];
+static loff_t log_buf_vaddr;
+static loff_t log_end_vaddr;
+static loff_t log_buf_len_vaddr;
+static loff_t logged_chars_vaddr;
+
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define ELFDATANATIVE ELFDATA2LSB
+#elif __BYTE_ORDER == __BIG_ENDIAN
+#define ELFDATANATIVE ELFDATA2MSB
+#else
+#error "Unknown machine endian"
+#endif
+
+static uint16_t file16_to_cpu(uint16_t val)
+{
+	if (ehdr.e_ident[EI_DATA] != ELFDATANATIVE)
+		val = bswap_16(val);
+	return val;
+}
+
+static uint32_t file32_to_cpu(uint32_t val)
+{
+	if (ehdr.e_ident[EI_DATA] != ELFDATANATIVE)
+		val = bswap_32(val);
+	return val;
+}
+
+static uint64_t file64_to_cpu(uint64_t val)
+{
+	if (ehdr.e_ident[EI_DATA] != ELFDATANATIVE)
+		val = bswap_64(val);
+	return val;
+}
+
+static uint64_t vaddr_to_offset(uint64_t vaddr)
+{
+	/* Just hand the simple case where kexec gets
+	 * the virtual address on the program headers right.
+	 */
+	ssize_t i;
+	for (i = 0; i < ehdr.e_phnum; i++) {
+		if (phdr[i].p_vaddr > vaddr)
+			continue;
+		if ((phdr[i].p_vaddr + phdr[i].p_memsz) <= vaddr)
+			continue;
+		return (vaddr - phdr[i].p_vaddr) + phdr[i].p_offset;
+	}
+	fprintf(stderr, "No program header covering vaddr 0x%llxfound kexec bug?\n",
+		(unsigned long long)vaddr);
+	exit(30);
+}
+
+static void read_elf32(int fd)
+{
+	Elf32_Ehdr ehdr32;
+	Elf32_Phdr *phdr32;
+	size_t phdrs32_size, phdrs_size;
+	ssize_t ret, i;
+
+	ret = pread(fd, &ehdr32, sizeof(ehdr32), 0);
+	if (ret != sizeof(ehdr32)) {
+		fprintf(stderr, "Read of Elf header from %s failed: %s\n",
+			fname, strerror(errno));
+		exit(10);
+	}
+
+	ehdr.e_type		= file16_to_cpu(ehdr32.e_type);
+	ehdr.e_machine		= file16_to_cpu(ehdr32.e_machine);
+	ehdr.e_version		= file32_to_cpu(ehdr32.e_version);
+	ehdr.e_entry		= file32_to_cpu(ehdr32.e_entry);
+	ehdr.e_phoff		= file32_to_cpu(ehdr32.e_phoff);
+	ehdr.e_shoff		= file32_to_cpu(ehdr32.e_shoff);
+	ehdr.e_flags		= file32_to_cpu(ehdr32.e_flags);
+	ehdr.e_ehsize		= file16_to_cpu(ehdr32.e_ehsize);
+	ehdr.e_phentsize	= file16_to_cpu(ehdr32.e_phentsize);
+	ehdr.e_phnum		= file16_to_cpu(ehdr32.e_phnum);
+	ehdr.e_shentsize	= file16_to_cpu(ehdr32.e_shentsize);
+	ehdr.e_shnum		= file16_to_cpu(ehdr32.e_shnum);
+	ehdr.e_shstrndx		= file16_to_cpu(ehdr32.e_shstrndx);
+	
+	if (ehdr.e_version != EV_CURRENT) {
+		fprintf(stderr, "Bad Elf header version %u\n",
+			ehdr.e_version);
+		exit(11);
+	}
+	if (ehdr.e_phentsize != sizeof(Elf32_Phdr)) {
+		fprintf(stderr, "Bad Elf progra header size %u expected %zu\n",
+			ehdr.e_phentsize, sizeof(Elf32_Phdr));
+		exit(12);
+	}
+	if (ehdr.e_phnum > ULONG_MAX/sizeof(Elf64_Phdr)) {
+		fprintf(stderr, "Too many elf program header entries\n");
+		exit(13);
+	}
+	phdrs32_size = ehdr.e_phnum * sizeof(Elf32_Phdr);
+	phdrs_size = ehdr.e_phnum * sizeof(Elf64_Phdr);
+	phdr32 = calloc(ehdr.e_phnum, sizeof(Elf32_Phdr));
+	if (!phdr32) {
+		fprintf(stderr, "Calloc of %u phdrs32 failed: %s\n",
+			ehdr.e_phnum, strerror(errno));
+		exit(14);
+	}
+	phdr = calloc(ehdr.e_phnum, sizeof(Elf64_Phdr));
+	if (!phdr) {
+		fprintf(stderr, "Calloc of %u phdrs failed: %s\n",
+			ehdr.e_phnum, strerror(errno));
+		exit(15);
+	}
+	ret = pread(fd, phdr32, phdrs32_size, ehdr.e_phoff);
+	if (ret != phdrs32_size) {
+		fprintf(stderr, "Read of program header @ 0x%llu for %zu bytes failed: %s\n",
+			(unsigned long long)ehdr.e_phoff, phdrs32_size, strerror(errno));
+		exit(16);
+	}
+	for (i = 0; i < ehdr.e_phnum; i++) {
+		phdr[i].p_type		= file32_to_cpu(phdr32[i].p_type);
+		phdr[i].p_offset	= file32_to_cpu(phdr32[i].p_offset);
+		phdr[i].p_vaddr		= file32_to_cpu(phdr32[i].p_vaddr);
+		phdr[i].p_paddr		= file32_to_cpu(phdr32[i].p_paddr);
+		phdr[i].p_filesz	= file32_to_cpu(phdr32[i].p_filesz);
+		phdr[i].p_memsz		= file32_to_cpu(phdr32[i].p_memsz);
+		phdr[i].p_flags		= file32_to_cpu(phdr32[i].p_flags);
+		phdr[i].p_align		= file32_to_cpu(phdr32[i].p_align);
+	}
+	free(phdr32);
+}
+
+
+static void read_elf64(int fd)
+{
+	Elf64_Ehdr ehdr64;
+	Elf64_Phdr *phdr64;
+	size_t phdrs_size;
+	ssize_t ret, i;
+
+	ret = pread(fd, &ehdr64, sizeof(ehdr64), 0);
+	if (ret != sizeof(ehdr)) {
+		fprintf(stderr, "Read of Elf header from %s failed: %s\n",
+			fname, strerror(errno));
+		exit(10);
+	}
+
+	ehdr.e_type		= file16_to_cpu(ehdr64.e_type);
+	ehdr.e_machine		= file16_to_cpu(ehdr64.e_machine);
+	ehdr.e_version		= file32_to_cpu(ehdr64.e_version);
+	ehdr.e_entry		= file64_to_cpu(ehdr64.e_entry);
+	ehdr.e_phoff		= file64_to_cpu(ehdr64.e_phoff);
+	ehdr.e_shoff		= file64_to_cpu(ehdr64.e_shoff);
+	ehdr.e_flags		= file32_to_cpu(ehdr64.e_flags);
+	ehdr.e_ehsize		= file16_to_cpu(ehdr64.e_ehsize);
+	ehdr.e_phentsize	= file16_to_cpu(ehdr64.e_phentsize);
+	ehdr.e_phnum		= file16_to_cpu(ehdr64.e_phnum);
+	ehdr.e_shentsize	= file16_to_cpu(ehdr64.e_shentsize);
+	ehdr.e_shnum		= file16_to_cpu(ehdr64.e_shnum);
+	ehdr.e_shstrndx		= file16_to_cpu(ehdr64.e_shstrndx);
+
+	if (ehdr.e_version != EV_CURRENT) {
+		fprintf(stderr, "Bad Elf header version %u\n",
+			ehdr.e_version);
+		exit(11);
+	}
+	if (ehdr.e_phentsize != sizeof(Elf64_Phdr)) {
+		fprintf(stderr, "Bad Elf progra header size %u expected %zu\n",
+			ehdr.e_phentsize, sizeof(Elf64_Phdr));
+		exit(12);
+	}
+	if (ehdr.e_phnum > ULONG_MAX/sizeof(Elf64_Phdr)) {
+		fprintf(stderr, "Too many program header entries\n");
+		exit(13);
+	}
+	phdrs_size = ehdr.e_phnum * sizeof(Elf64_Phdr);
+	phdr64 = calloc(ehdr.e_phnum, sizeof(Elf64_Phdr));
+	if (!phdr64) {
+		fprintf(stderr, "Calloc of %u phdrs64 failed: %s\n",
+			ehdr.e_phnum, strerror(errno));
+		exit(14);
+	}
+	phdr = calloc(ehdr.e_phnum, sizeof(Elf64_Phdr));
+	if (!phdr) {
+		fprintf(stderr, "Calloc of %u phdrs failed: %s\n",
+			ehdr.e_phnum, strerror(errno));
+		exit(15);
+	}
+	ret = pread(fd, phdr64, phdrs_size, ehdr.e_phoff);
+	if (ret != phdrs_size) {
+		fprintf(stderr, "Read of program header @ %llu for %zu bytes failed: %s\n",
+			(unsigned long long)(ehdr.e_phoff), phdrs_size, strerror(errno));
+		exit(16);
+	}
+	for (i = 0; i < ehdr.e_phnum; i++) {
+		phdr[i].p_type		= file32_to_cpu(phdr64[i].p_type);
+		phdr[i].p_flags		= file32_to_cpu(phdr64[i].p_flags);
+		phdr[i].p_offset	= file64_to_cpu(phdr64[i].p_offset);
+		phdr[i].p_vaddr		= file64_to_cpu(phdr64[i].p_vaddr);
+		phdr[i].p_paddr		= file64_to_cpu(phdr64[i].p_paddr);
+		phdr[i].p_filesz	= file64_to_cpu(phdr64[i].p_filesz);
+		phdr[i].p_memsz		= file64_to_cpu(phdr64[i].p_memsz);
+		phdr[i].p_align		= file64_to_cpu(phdr64[i].p_align);
+	}
+	free(phdr64);
+}
+
+static void scan_vmcoreinfo(char *start, size_t size)
+{
+	char *last = start + size - 1;
+	char *pos, *eol;
+#define SYMBOL(sym) {					\
+	.str = "SYMBOL(" #sym  ")=",			\
+	.name = #sym,					\
+	.len = sizeof("SYMBOL(" #sym  ")=") - 1,	\
+	.vaddr = & sym ## _vaddr,			\
+ }
+	static struct symbol {
+		const char *str;
+		const char *name;
+		size_t len;
+		loff_t *vaddr;
+	} symbol[] = {
+		SYMBOL(log_buf),
+		SYMBOL(log_end),
+		SYMBOL(log_buf_len),
+		SYMBOL(logged_chars),
+	};
+
+	for (pos = start; pos <= last; pos = eol + 1) {
+		size_t len;
+		int i;
+		/* Find the end of the current line */
+		for (eol = pos; (eol <= last) && (*eol != '\n') ; eol++)
+			;
+		len = eol - pos + 1;
+		/* Stomp the last character so I am guaranteed a terminating null */
+		*eol = '\0';
+		/* Copy OSRELEASE if I see it */
+		if ((len >= 10) && (memcmp("OSRELEASE=", pos, 10) == 0)) {
+			size_t to_copy = len - 10;
+			if (to_copy >= sizeof(osrelease))
+				to_copy = sizeof(osrelease) - 1;
+			memcpy(osrelease, pos + 10, to_copy);
+			osrelease[to_copy] = '\0';
+		}
+		/* See if the line is mentions a symbol I am looking for */
+		for (i = 0; i < sizeof(symbol)/sizeof(symbol[0]); i++ ) {
+			unsigned long long vaddr;
+			if (symbol[i].len >= len)
+				continue;
+			if (memcmp(symbol[i].str, pos, symbol[i].len) != 0)
+				continue;
+			/* Found a symbol now decode it */
+			vaddr = strtoull(pos + symbol[i].len, NULL, 16);
+			/* Remember the virtual address */
+			*symbol[i].vaddr = vaddr;
+		}
+	}
+}
+
+static void scan_notes(int fd, loff_t start, loff_t lsize)
+{
+	char *buf, *last, *note, *next;
+	size_t size;
+	ssize_t ret;
+
+	if (lsize > LONG_MAX) {
+		fprintf(stderr, "Unable to handle note section of %llu bytes\n",
+			(unsigned long long)lsize);
+		exit(20);
+	}
+	size = lsize;
+	buf = malloc(size);
+	if (!buf) {
+		fprintf(stderr, "Cannot malloc %zu bytes\n", size);
+		exit(21);
+	}
+	last = buf + size - 1;
+	ret = pread(fd, buf, size, start);
+	if (ret != size) {
+		fprintf(stderr, "Cannot read note section @ 0x%llx of %zu bytes: %s\n",
+			(unsigned long long)start, size, strerror(errno));
+		exit(22);
+	}
+
+	for (note = buf; (note + sizeof(Elf_Nhdr)) < last; note = next)
+	{
+		Elf_Nhdr *hdr;
+		char *n_name, *n_desc;
+		size_t n_namesz, n_descsz, n_type;
+		
+		hdr = (Elf_Nhdr *)note;
+		n_namesz = file32_to_cpu(hdr->n_namesz);
+		n_descsz = file32_to_cpu(hdr->n_descsz);
+		n_type   = file32_to_cpu(hdr->n_type);
+
+		n_name = note + sizeof(*hdr);
+		n_desc = n_name + ((n_namesz + 3) & ~3);
+		next = n_desc + ((n_descsz + 3) & ~3);
+
+		if (next > (last + 1))
+			break;
+
+		if ((memcmp(n_name, "VMCOREINFO", 11) != 0) || (n_type != 0))
+			continue;
+		scan_vmcoreinfo(n_desc, n_descsz);
+	}
+	free(buf);
+}
+
+static void scan_note_headers(int fd)
+{
+	int i;
+	for (i = 0; i < ehdr.e_phnum; i++) {
+		if (phdr[i].p_type != PT_NOTE)
+			continue;
+		scan_notes(fd, phdr[i].p_offset, phdr[i].p_filesz);
+	}
+}
+
+static uint64_t read_file_pointer(int fd, uint64_t addr)
+{
+	uint64_t result;
+	ssize_t ret;
+	if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
+		uint64_t scratch;
+		ret = pread(fd, &scratch, sizeof(scratch), addr);
+		if (ret != sizeof(scratch)) {
+			fprintf(stderr, "Failed to read pointer @ 0x%llx: %s\n",
+				(unsigned long long)addr, strerror(errno));
+			exit(40);
+		}
+		result = file64_to_cpu(scratch);
+	} else {
+		uint32_t scratch;
+		ret = pread(fd, &scratch, sizeof(scratch), addr);
+		if (ret != sizeof(scratch)) {
+			fprintf(stderr, "Failed to read pointer @ 0x%llx: %s\n",
+				(unsigned long long)addr, strerror(errno));
+			exit(40);
+		}
+		result = file32_to_cpu(scratch);
+	}
+	return result;
+}
+
+static uint32_t read_file_u32(int fd, uint64_t addr)
+{
+	uint32_t scratch;
+	ssize_t ret;
+	ret = pread(fd, &scratch, sizeof(scratch), addr);
+	if (ret != sizeof(scratch)) {
+		fprintf(stderr, "Failed to read value @ 0x%llx: %s\n",
+			(unsigned long long)addr, strerror(errno));
+		exit(41);
+	}
+	return file32_to_cpu(scratch);
+}
+
+static int32_t read_file_s32(int fd, uint64_t addr)
+{
+	return read_file_u32(fd, addr);
+}
+
+static void dump_dmesg(int fd)
+{
+	uint64_t log_buf, log_buf_offset;
+	unsigned log_end, logged_chars, log_end_wrapped;
+	int log_buf_len, to_wrap;
+	char *buf;
+	ssize_t ret;
+
+	if (!log_buf_vaddr) {
+		fprintf(stderr, "Missing the log_buf symbol\n");
+		exit(50);
+	}
+	if (!log_end_vaddr) {
+		fprintf(stderr, "Missing the log_end symbol\n");
+		exit(51);
+	}
+	if (!log_buf_len_vaddr) {
+		fprintf(stderr, "Missing the log_bug_len symbol\n");
+		exit(52);
+	}
+	if (!logged_chars_vaddr) {
+		fprintf(stderr, "Missing the logged_chars symbol\n");
+		exit(53);
+	}
+
+
+	log_buf = read_file_pointer(fd, vaddr_to_offset(log_buf_vaddr));
+	log_end = read_file_u32(fd, vaddr_to_offset(log_end_vaddr));
+	log_buf_len = read_file_s32(fd, vaddr_to_offset(log_buf_len_vaddr));
+	logged_chars = read_file_u32(fd, vaddr_to_offset(logged_chars_vaddr));
+
+	log_buf_offset = vaddr_to_offset(log_buf);
+
+	buf = calloc(1, log_buf_len);
+	if (!buf) {
+		fprintf(stderr, "Failed to malloc %d bytes for the logbuf: %s\n",
+			log_buf_len, strerror(errno));
+		exit(51);
+	}
+
+	log_end_wrapped = log_end % log_buf_len;
+	to_wrap = log_buf_len - log_end_wrapped;
+
+	ret = pread(fd, buf, to_wrap, log_buf_offset + log_end_wrapped);
+	if (ret != to_wrap) {
+		fprintf(stderr, "Failed to read the first half of the log buffer: %s\n",
+			strerror(errno));
+		exit(52);
+	}
+	ret = pread(fd, buf + to_wrap, log_end_wrapped, log_buf_offset);
+	if (ret != log_end_wrapped) {
+		fprintf(stderr, "Faield to read the second half of the log buffer: %s\n",
+			strerror(errno));
+		exit(53);
+	}
+	ret = write(STDOUT_FILENO, buf + (log_buf_len -  logged_chars), logged_chars);
+	if (ret != logged_chars) {
+		fprintf(stderr, "Failed to write out the dmesg log buffer!: %s\n",
+			strerror(errno));
+		exit(54);
+	}
+}
+
+int main(int argc, char **argv)
+{
+	ssize_t ret;
+	int fd;
+
+	if (argc != 2) {
+		fprintf(stderr, "usage: %s <kernel core file>\n", argv[0]);
+		return 1;
+	}
+	fname = argv[1];
+
+	fd = open(fname, O_RDONLY);
+	if (fd < 0) {
+		fprintf(stderr, "Cannot open %s: %s\n",
+			fname, strerror(errno));
+		return 2;
+	}
+	ret = pread(fd, ehdr.e_ident, EI_NIDENT, 0);
+	if (ret != EI_NIDENT) {
+		fprintf(stderr, "Read of e_ident from %s failed: %s\n",
+			fname, strerror(errno));
+		return 3;
+	}
+	if (memcmp(ehdr.e_ident, ELFMAG, SELFMAG) != 0) {
+		fprintf(stderr, "Missing elf signature\n");
+		return 4;
+	}
+	if (ehdr.e_ident[EI_VERSION] != EV_CURRENT) {
+		fprintf(stderr, "Bad elf version\n");
+		return 5;
+	}
+	if ((ehdr.e_ident[EI_CLASS] != ELFCLASS32) &&
+	    (ehdr.e_ident[EI_CLASS] != ELFCLASS64))
+	{
+		fprintf(stderr, "Unknown elf class %u\n",
+			ehdr.e_ident[EI_CLASS]);
+		return 6;
+	}
+	if ((ehdr.e_ident[EI_DATA] != ELFDATA2LSB) &&
+	    (ehdr.e_ident[EI_DATA] != ELFDATA2MSB))
+	{
+		fprintf(stderr, "Unkown elf data order %u\n",
+			ehdr.e_ident[EI_DATA]);
+		return 7;
+	}
+	if (ehdr.e_ident[EI_CLASS] == ELFCLASS32)
+		read_elf32(fd);
+	else
+		read_elf64(fd);
+
+	scan_note_headers(fd);
+	dump_dmesg(fd);
+	close(fd);
+
+	return 0;
+}