dwarves: Allow the apps to steal compile units as they are created

So that we immensely reduce the memory footprint by doing filtering and
other processing/pretty printing as the cus are loaded, discarding them
right away.

The next cset will use this scheme in pahole.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

ctf_loader.c

@@ -866,24 +866,10 @@ static int cu__fixup_ctf_bitfields(struct cu *self)
 	return err;
 }
 
-static int cus__fixup_ctf_bitfields(struct cus *self)
-{
-	int err = 0;
-	struct cu *pos;
-
-	list_for_each_entry(pos, &self->cus, node) {
-		err = cu__fixup_ctf_bitfields(pos);
-		if (err)
-			break;
-	}
-	return err;
-}
-
-int ctf__load(struct cus *self, struct conf_load *conf __unused,
-	      const char *filename)
+int ctf__load(struct cus *self, struct conf_load *conf, const char *filename)
 {
 	struct ctf_state state;
-	int wordsize;
+	int wordsize, err;
 
 	memset(&state, 0, sizeof(state));
 
@@ -907,13 +893,20 @@ int ctf__load(struct cus *self, struct conf_load *conf __unused,
 	if (state.cu == NULL)
 		oom("cu__new");
 
-	cus__add(self, state.cu);
-
 	dump_ctf(&state);
 
 	elf_end(state.elf);
 
 	close(state.in_fd);
 
-	return cus__fixup_ctf_bitfields(self);
+	err = cu__fixup_ctf_bitfields(state.cu);
+	/*
+	 * The app stole this cu, possibly deleting it,
+	 * so forget about it
+	 */
+	if (conf->steal && conf->steal(state.cu, conf))
+		return 0;
+
+	cus__add(self, state.cu);
+	return err;
 }

dwarf_loader.c

@@ -1582,8 +1582,8 @@ static void die__process(Dwarf_Die *die, struct cu *cu)
 	cu__recode_dwarf_types(cu);
 }
 
-static void cus__load_module(struct cus *self, struct conf_load *conf,
-			     Dwfl_Module *mod, Dwarf *dw)
+static int cus__load_module(struct cus *self, struct conf_load *conf,
+			    Dwfl_Module *mod, Dwarf *dw)
 {
 	Dwarf_Off off = 0, noff;
 	size_t cuhl;
@@ -1609,11 +1609,29 @@ static void cus__load_module(struct cus *self, struct conf_load *conf,
 			oom("cu__new");
 		cu->extra_dbg_info = conf ? conf->extra_dbg_info : 0;
 		die__process(cu_die, cu);
-		cus__add(self, cu);
+		off = noff;
+		if (conf->steal != NULL) {
+			switch (conf->steal(cu, conf)) {
+			case LSK__STOP_LOADING:
+				return DWARF_CB_ABORT;
+			case LSK__STOLEN:
+				/*
+				 * The app stole this cu, possibly deleting it,
+				 * so forget about it:
+				 */
+				continue;
+			case LSK__KEEPIT:
+				break;
+			}
+		}
+
 		if (!cu->extra_dbg_info)
 			cu__for_all_tags(cu, tag__delete_priv, NULL);
-		off = noff;
+
+		cus__add(self, cu);
 	}
+	
+	return DWARF_CB_OK;
 }
 
 struct process_dwflmod_parms {
@@ -1641,9 +1659,10 @@ static int cus__process_dwflmod(Dwfl_Module *dwflmod,
 	Dwarf_Addr dwbias;
 	Dwarf *dw = dwfl_module_getdwarf(dwflmod, &dwbias);
 
+	int err = DWARF_CB_OK;
 	if (dw != NULL) {
 		++parms->nr_dwarf_sections_found;
-		cus__load_module(self, parms->conf, dwflmod, dw);
+		err = cus__load_module(self, parms->conf, dwflmod, dw);
 	}
 	/*
 	 * XXX We will fall back to try finding other debugging
@@ -1655,7 +1674,7 @@ static int cus__process_dwflmod(Dwfl_Module *dwflmod,
 	 *	__func__, dwfl_errmsg(-1));
 	 */
 
-	return DWARF_CB_OK;
+	return err;
 }
 
 static int cus__process_file(struct cus *self, struct conf_load *conf, int fd,

dwarves.h

@@ -21,12 +21,23 @@
 
 extern struct strings *strings;
 
+struct cu;
+
+enum load_steal_kind {
+	LSK__KEEPIT,
+	LSK__STOLEN,
+	LSK__STOP_LOADING,
+};
+
 /** struct conf_load - load configuration
  * @extra_dbg_info - keep original debugging format extra info
  *		     (e.g. DWARF's decl_{line,file}, id, etc)
  */
 struct conf_load {
-	bool	   extra_dbg_info;
+	bool			extra_dbg_info;
+	enum load_steal_kind	(*steal)(struct cu *self,
+					 struct conf_load *conf);
+	void			*cookie;
 };
 
 struct cus {