objtool: Free insns when done

Free the decoded instructions as they're no longer needed after this
point.  This frees up a big chunk of heap, which will come handy when
skipping the reading of DWARF section data.

Link: https://lore.kernel.org/r/4d4bca1a0f869de020dac80d91f9acbf6df77eab.1685464332.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

tools/objtool/check.c

@@ -4596,6 +4596,34 @@ static int disas_warned_funcs(struct objtool_file *file)
 	return 0;
 }
 
+struct insn_chunk {
+	void *addr;
+	struct insn_chunk *next;
+};
+
+/*
+ * Reduce peak RSS usage by freeing insns memory before writing the ELF file,
+ * which can trigger more allocations for .debug_* sections whose data hasn't
+ * been read yet.
+ */
+static void free_insns(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct insn_chunk *chunks = NULL, *chunk;
+
+	for_each_insn(file, insn) {
+		if (!insn->idx) {
+			chunk = malloc(sizeof(*chunk));
+			chunk->addr = insn;
+			chunk->next = chunks;
+			chunks = chunk;
+		}
+	}
+
+	for (chunk = chunks; chunk; chunk = chunk->next)
+		free(chunk->addr);
+}
+
 int check(struct objtool_file *file)
 {
 	int ret, warnings = 0;
@@ -4742,6 +4770,8 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}
 
+	free_insns(file);
+
 	if (opts.verbose)
 		disas_warned_funcs(file);