Index: sys/conf/ldscript.amd64
===================================================================
--- sys/conf/ldscript.amd64
+++ sys/conf/ldscript.amd64
@@ -83,6 +83,11 @@
   PROVIDE (brwsection = .);
   /* Exception handling  */
   .eh_frame       : ONLY_IF_RW { KEEP (*(.eh_frame)) }
+  .note.gnu.build-id : {
+    PROVIDE (__buildid_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__buildid_end = .);
+  }
   .gcc_except_table   : ONLY_IF_RW { *(.gcc_except_table .gcc_except_table.*) }
   /* Thread Local Storage sections  */
   .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
Index: sys/kern/kern_mib.c
===================================================================
--- sys/kern/kern_mib.c
+++ sys/kern/kern_mib.c
@@ -481,6 +481,45 @@
     CTLTYPE_INT | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
     NULL, 0, sysctl_osreldate, "I", "Kernel release date");
 
+/*
+ * The buildid is copied from the ELF section .note.gnu.build-id.  The linker 
+ * script defines two variables to expose the beginning and end.  LLVM 
+ * currently uses a SHA-1 hash, but other formats can be supported by checking 
+ * the length of the section.
+ */
+
+extern char __buildid_start[];
+extern char __buildid_end[];
+
+static int
+sysctl_buildid(SYSCTL_HANDLER_ARGS)
+{
+	uintptr_t sectionlen = (uintptr_t)(__buildid_end - __buildid_start);
+	int hashlen = 20;
+	char buf[41];
+
+	if (sectionlen != 0x24) {
+	    return (ENOENT);
+	}
+
+	/*
+	 * The ELF note section has a four byte length for the vendor name,
+	 * four byte length for the value, and a four byte vendor specific 
+	 * type.  The name for the build id is "GNU\0".  We skip the first 16 
+	 * bytes to read the build hash.
+	 */
+	for (int i = 0; i < hashlen; i++) {
+	    uint8_t c = __buildid_start[i+0x10];
+	    snprintf(&buf[2*i], 3, "%02x", c);
+	}
+
+	return (SYSCTL_OUT(req, buf, strlen(buf) + 1));
+}
+
+SYSCTL_PROC(_kern, OID_AUTO, buildid,
+    CTLTYPE_STRING | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
+    NULL, 0, sysctl_buildid, "A", "Operating system buildid");
+
 SYSCTL_NODE(_kern, OID_AUTO, features, CTLFLAG_RD, 0, "Kernel Features");
 
 #ifdef COMPAT_FREEBSD4
Index: usr.bin/uname/uname.c
===================================================================
--- usr.bin/uname/uname.c
+++ usr.bin/uname/uname.c
@@ -67,9 +67,10 @@
 #define	IFLAG	0x40
 #define	UFLAG	0x80
 #define	KFLAG	0x100
+#define BFLAG	0x200
 
 typedef void (*get_t)(void);
-static get_t get_ident, get_platform, get_hostname, get_arch,
+static get_t get_buildid, get_ident, get_platform, get_hostname, get_arch,
     get_release, get_sysname, get_kernvers, get_uservers, get_version;
 
 static void native_ident(void);
@@ -81,11 +82,13 @@
 static void native_version(void);
 static void native_kernvers(void);
 static void native_uservers(void);
+static void native_buildid(void);
 static void print_uname(u_int);
 static void setup_get(void);
 static void usage(void);
 
-static char *ident, *platform, *hostname, *arch, *release, *sysname, *version, *kernvers, *uservers;
+static char *buildid, *ident, *platform, *hostname, *arch,
+    *release, *sysname, *version, *kernvers, *uservers;
 static int space;
 
 int
@@ -97,10 +100,13 @@
 	setup_get();
 	flags = 0;
 
-	while ((ch = getopt(argc, argv, "aiKmnoprsUv")) != -1)
+	while ((ch = getopt(argc, argv, "abiKmnoprsUv")) != -1)
 		switch(ch) {
 		case 'a':
-			flags |= (MFLAG | NFLAG | RFLAG | SFLAG | VFLAG);
+			flags |= (BFLAG | MFLAG | NFLAG | RFLAG | SFLAG | VFLAG);
+			break;
+		case 'b':
+			flags |= BFLAG;
 			break;
 		case 'i':
 			flags |= IFLAG;
@@ -169,6 +175,7 @@
 	CHECK_ENV("i", ident);
 	CHECK_ENV("K", kernvers);
 	CHECK_ENV("U", uservers);
+	CHECK_ENV("b", buildid);
 }
 
 #define	PRINT_FLAG(flags,flag,var)		\
@@ -194,6 +201,7 @@
 	PRINT_FLAG(flags, IFLAG, ident);
 	PRINT_FLAG(flags, KFLAG, kernvers);
 	PRINT_FLAG(flags, UFLAG, uservers);
+	PRINT_FLAG(flags, BFLAG, buildid);
 	printf("\n");
 }
 
@@ -261,6 +269,9 @@
 NATIVE_SYSCTLNAME_GET(ident, "kern.ident") {
 } NATIVE_SET;
 
+NATIVE_SYSCTLNAME_GET(buildid, "kern.buildid") {
+} NATIVE_SET;
+
 static void
 native_uservers(void)
 {
@@ -282,6 +293,6 @@
 static void
 usage(void)
 {
-	fprintf(stderr, "usage: uname [-aiKmnoprsUv]\n");
+	fprintf(stderr, "usage: uname [-abiKmnoprsUv]\n");
 	exit(1);
 }