3 files changed, 140 insertions, 0 deletions
diff --git a/vmcore-dmesg/Makefile b/vmcore-dmesg/Makefile
new file mode 100644
index 0000000..b147f26
--- /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) $(UTIL_LIB)
+	@$(MKDIR) -p $(@D)
+	$(LINK.o) -o $@ $^ $(CFLAGS) $(LIBS)
+
+$(VMCORE_DMESG_MANPAGE): vmcore-dmesg/vmcore-dmesg.8
+	$(MKDIR) -p     $(MANDIR)/man8
+	cp $^ $(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..ec594b0
--- /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 21, 2020"
+.\" 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
+.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..122e536
--- /dev/null
+++ b/vmcore-dmesg/vmcore-dmesg.c
@@ -0,0 +1,69 @@
+#include <elf_info.h>
+
+/* The 32bit and 64bit note headers make it clear we don't care */
+typedef Elf32_Nhdr Elf_Nhdr;
+
+extern const char *fname;
+
+/* stole this macro from kernel printk.c */
+#define LOG_BUF_LEN_MAX (uint32_t)(1U << 31)
+
+static void write_to_stdout(char *buf, unsigned int nr)
+{
+	ssize_t ret;
+	static uint32_t n_bytes = 0;
+
+	n_bytes += nr;
+	if (n_bytes > LOG_BUF_LEN_MAX) {
+		fprintf(stderr, "The vmcore-dmesg.txt over 2G in size is not supported.\n");
+		exit(53);
+	}
+
+	ret = write(STDOUT_FILENO, buf, nr);
+	if (ret != nr) {
+		fprintf(stderr, "Failed to write out the dmesg log buffer!:"
+			" %s\n", strerror(errno));
+		exit(54);
+	}
+}
+
+static int read_vmcore_dmesg(int fd, void (*handler)(char*, unsigned int))
+{
+	int ret;
+
+	ret = read_elf(fd);
+	if (ret > 0) {
+		fprintf(stderr, "Unable to read ELF information"
+			" from vmcore\n");
+		return ret;
+	}
+
+	dump_dmesg(fd, handler);
+
+	return 0;
+}
+
+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 = read_vmcore_dmesg(fd, write_to_stdout);
+	
+	close(fd);
+
+	return ret;
+}