Index: head/sys/conf/ldscript.amd64
===================================================================
--- head/sys/conf/ldscript.amd64
+++ head/sys/conf/ldscript.amd64
@@ -74,6 +74,11 @@
   PROVIDE (etext = .);
   .rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
   .rodata1        : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .eh_frame_hdr : { *(.eh_frame_hdr) }
   .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
   .gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }
Index: head/sys/conf/ldscript.arm
===================================================================
--- head/sys/conf/ldscript.arm
+++ head/sys/conf/ldscript.arm
@@ -27,6 +27,11 @@
   .gnu.version   : { *(.gnu.version)	}
   .gnu.version_d   : { *(.gnu.version_d)	}
   .gnu.version_r   : { *(.gnu.version_r)	}
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.text      :
     { *(.rel.text) *(.rel.gnu.linkonce.t*) }
   .rela.text     :
Index: head/sys/conf/ldscript.arm64
===================================================================
--- head/sys/conf/ldscript.arm64
+++ head/sys/conf/ldscript.arm64
@@ -27,6 +27,11 @@
   .gnu.version   : { *(.gnu.version)	}
   .gnu.version_d   : { *(.gnu.version_d)	}
   .gnu.version_r   : { *(.gnu.version_r)	}
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.text      :
     { *(.rel.text) *(.rel.gnu.linkonce.t*) }
   .rela.text     :
Index: head/sys/conf/ldscript.i386
===================================================================
--- head/sys/conf/ldscript.i386
+++ head/sys/conf/ldscript.i386
@@ -62,6 +62,11 @@
   PROVIDE (etext = .);
   .rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
   .rodata1        : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .eh_frame_hdr : { *(.eh_frame_hdr) }
   .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
   .gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }
Index: head/sys/conf/ldscript.mips
===================================================================
--- head/sys/conf/ldscript.mips
+++ head/sys/conf/ldscript.mips
@@ -63,6 +63,11 @@
   .gnu.version   : { *(.gnu.version)	}
   .gnu.version_d   : { *(.gnu.version_d)	}
   .gnu.version_r   : { *(.gnu.version_r)	}
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.init      : { *(.rel.init)	}
   .rela.init     : { *(.rela.init)	}
   .rel.text      :
Index: head/sys/conf/ldscript.mips.cfe
===================================================================
--- head/sys/conf/ldscript.mips.cfe
+++ head/sys/conf/ldscript.mips.cfe
@@ -192,6 +192,11 @@
   PROVIDE (etext = .);
   .rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .reginfo : { *(.reginfo) }
   .sdata2   : { *(.sdata2) *(.sdata2.*) *(.gnu.linkonce.s2.*) }
   .sbss2   : { *(.sbss2) *(.sbss2.*) *(.gnu.linkonce.sb2.*) }
Index: head/sys/conf/ldscript.mips.mips64
===================================================================
--- head/sys/conf/ldscript.mips.mips64
+++ head/sys/conf/ldscript.mips.mips64
@@ -176,6 +176,11 @@
   PROVIDE (etext = .);
   .rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .reginfo : { *(.reginfo) }
   .sdata2   : { *(.sdata2) *(.sdata2.*) *(.gnu.linkonce.s2.*) }
   .sbss2   : { *(.sbss2) *(.sbss2.*) *(.gnu.linkonce.sb2.*) }
Index: head/sys/conf/ldscript.mips.octeon1
===================================================================
--- head/sys/conf/ldscript.mips.octeon1
+++ head/sys/conf/ldscript.mips.octeon1
@@ -23,6 +23,12 @@
 	    	*(.rodata)
 		. = ALIGN(32);
 	}
+
+	.note.gnu.build-id : {
+		PROVIDE (__build_id_start = .);
+		*(.note.gnu.build-id)
+		PROVIDE (__build_id_end = .);
+	}
 	
 	.data : {
                 _rwdata = .;
Index: head/sys/conf/ldscript.powerpc
===================================================================
--- head/sys/conf/ldscript.powerpc
+++ head/sys/conf/ldscript.powerpc
@@ -55,6 +55,11 @@
   .fini      : { *(.fini)    } =0
   .rodata    : { *(.rodata) *(.gnu.linkonce.r*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .sdata2    : { *(.sdata2)  }
   .sbss2     : { *(.sbss2)   }
   /* Adjust the address for the data segment to the next page up. */
Index: head/sys/conf/ldscript.powerpc64
===================================================================
--- head/sys/conf/ldscript.powerpc64
+++ head/sys/conf/ldscript.powerpc64
@@ -46,6 +46,11 @@
   .gnu.version   : { *(.gnu.version)	}
   .gnu.version_d   : { *(.gnu.version_d)	}
   .gnu.version_r   : { *(.gnu.version_r)	}
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rela.text     :
     { *(.rela.text) *(.rela.gnu.linkonce.t*) }
   .rela.data     :
Index: head/sys/conf/ldscript.powerpcspe
===================================================================
--- head/sys/conf/ldscript.powerpcspe
+++ head/sys/conf/ldscript.powerpcspe
@@ -55,6 +55,11 @@
   .fini      : { *(.fini)    } =0
   .rodata    : { *(.rodata) *(.gnu.linkonce.r*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .sdata2    : { *(.sdata2)  }
   .sbss2     : { *(.sbss2)   }
   /* Adjust the address for the data segment to the next page up. */
Index: head/sys/conf/ldscript.riscv
===================================================================
--- head/sys/conf/ldscript.riscv
+++ head/sys/conf/ldscript.riscv
@@ -27,6 +27,11 @@
   .gnu.version   : { *(.gnu.version)	}
   .gnu.version_d   : { *(.gnu.version_d)	}
   .gnu.version_r   : { *(.gnu.version_r)	}
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.text      :
     { *(.rel.text) *(.rel.gnu.linkonce.t*) }
   .rela.text     :
Index: head/sys/conf/ldscript.sparc64
===================================================================
--- head/sys/conf/ldscript.sparc64
+++ head/sys/conf/ldscript.sparc64
@@ -146,6 +146,11 @@
   PROVIDE (etext = .);
   .rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .sdata2   : { *(.sdata2) *(.sdata2.*) *(.gnu.linkonce.s2.*) }
   .sbss2   : { *(.sbss2) *(.sbss2.*) *(.gnu.linkonce.sb2.*) }
   . = ALIGN(0x2000) + (. & (0x2000 - 1));
Index: head/sys/kern/kern_mib.c
===================================================================
--- head/sys/kern/kern_mib.c
+++ head/sys/kern/kern_mib.c
@@ -481,6 +481,54 @@
     CTLTYPE_INT | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
     NULL, 0, sysctl_osreldate, "I", "Kernel release date");
 
+/*
+ * The build-id 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 __build_id_start[];
+extern char __build_id_end[];
+
+#define	BUILD_ID_HEADER_LEN	0x10
+#define	BUILD_ID_HASH_MAXLEN	0x14
+
+static int
+sysctl_build_id(SYSCTL_HANDLER_ARGS)
+{
+	uintptr_t sectionlen = (uintptr_t)(__build_id_end - __build_id_start);
+	int hashlen;
+	char buf[2*BUILD_ID_HASH_MAXLEN+1];
+
+	/*
+	 * 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.  We will return the remaining bytes up 
+	 * to 20 (SHA-1) hash size.  If the hash happens to be a custom number 
+	 * of bytes we will pad the value with zeros, as the section should be 
+	 * four byte aligned.
+	 */
+	if (sectionlen <= BUILD_ID_HEADER_LEN ||
+	    sectionlen > (BUILD_ID_HEADER_LEN + BUILD_ID_HASH_MAXLEN)) {
+	    return (ENOENT);
+	}
+   
+
+	hashlen = sectionlen - BUILD_ID_HEADER_LEN;
+	for (int i = 0; i < hashlen; i++) {
+	    uint8_t c = __build_id_start[i+BUILD_ID_HEADER_LEN];
+	    snprintf(&buf[2*i], 3, "%02x", c);
+	}
+
+	return (SYSCTL_OUT(req, buf, strlen(buf) + 1));
+}
+
+SYSCTL_PROC(_kern, OID_AUTO, build_id,
+    CTLTYPE_STRING | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
+    NULL, 0, sysctl_build_id, "A", "Operating system build-id");
+
 SYSCTL_NODE(_kern, OID_AUTO, features, CTLFLAG_RD, 0, "Kernel Features");
 
 #ifdef COMPAT_FREEBSD4