Index: contrib/elftoolchain/libdwarf/libdwarf_lineno.c
===================================================================
--- contrib/elftoolchain/libdwarf/libdwarf_lineno.c
+++ contrib/elftoolchain/libdwarf/libdwarf_lineno.c
@@ -33,7 +33,7 @@
     Dwarf_Error *error, Dwarf_Debug dbg)
 {
 	Dwarf_LineFile lf;
-	const char *dirname;
+	const char *basedir, *incdir;
 	uint8_t *src;
 	int slen;
 
@@ -56,18 +56,33 @@
 
 	/* Make full pathname if need. */
 	if (*lf->lf_fname != '/') {
-		dirname = compdir;
-		if (lf->lf_dirndx > 0)
-			dirname = li->li_incdirs[lf->lf_dirndx - 1];
-		if (dirname != NULL) {
-			slen = strlen(dirname) + strlen(lf->lf_fname) + 2;
+		basedir = incdir = NULL;
+		if (lf->lf_dirndx > 0) {
+			incdir = li->li_incdirs[lf->lf_dirndx - 1];
+			if (incdir[0] == '/')
+				basedir = incdir;
+		} else {
+			basedir = compdir;
+		}
+		if (basedir != NULL) {
+			slen = strlen(basedir) + strlen(lf->lf_fname) + 2;
 			if ((lf->lf_fullpath = malloc(slen)) == NULL) {
 				free(lf);
 				DWARF_SET_ERROR(dbg, error, DW_DLE_MEMORY);
 				return (DW_DLE_MEMORY);
 			}
-			snprintf(lf->lf_fullpath, slen, "%s/%s", dirname,
+			snprintf(lf->lf_fullpath, slen, "%s/%s", basedir,
 			    lf->lf_fname);
+		} else if (incdir != NULL) {
+			slen = strlen(compdir) + strlen(incdir) +
+			    strlen(lf->lf_fname) + 3;
+			if ((lf->lf_fullpath = malloc(slen)) == NULL) {
+				free(lf);
+				DWARF_SET_ERROR(dbg, error, DW_DLE_MEMORY);
+				return (DW_DLE_MEMORY);
+			}
+			snprintf(lf->lf_fullpath, slen, "%s/%s/%s", compdir,
+			    incdir, lf->lf_fname);
 		}
 	}
 
Index: sys/conf/kern.post.mk
===================================================================
--- sys/conf/kern.post.mk
+++ sys/conf/kern.post.mk
@@ -358,11 +358,6 @@
 .endif
 .endfor
 
-.if defined(_MAP_DEBUG_PREFIX)
-# Ensure that DWARF info contains a full path for auto-generated headers.
-CFLAGS+= -fdebug-prefix-map=.=${.OBJDIR}
-.endif
-
 ${_ILINKS}:
 	@case ${.TARGET} in \
 	machine) \
Index: sys/conf/kmod.mk
===================================================================
--- sys/conf/kmod.mk
+++ sys/conf/kmod.mk
@@ -302,11 +302,6 @@
 .endif
 .endfor
 
-.if defined(_MAP_DEBUG_PREFIX)
-# Ensure that DWARF info contains a full path for auto-generated headers.
-CFLAGS+= -fdebug-prefix-map=.=${.OBJDIR}
-.endif
-
 .NOPATH: ${_ILINKS}
 
 ${_ILINKS}: