objtool: Add the --disas=<function-pattern> action

Add the --disas=<function-pattern> actions to disassemble the specified
functions. The function pattern can be a single function name (e.g.
--disas foo to disassemble the function with the name "foo"), or a shell
wildcard pattern (e.g. --disas foo* to disassemble all functions with a
name starting with "foo").

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/20251121095340.464045-18-alexandre.chartre@oracle.com

tools/objtool/builtin-check.c

@@ -75,6 +75,7 @@ static const struct option check_options[] = {
 	OPT_GROUP("Actions:"),
 	OPT_BOOLEAN(0,		 "checksum", &opts.checksum, "generate per-function checksums"),
 	OPT_BOOLEAN(0,		 "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
+	OPT_STRING_OPTARG('d',	 "disas", &opts.disas, "function-pattern", "disassemble functions", "*"),
 	OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr,skylake", "patch toolchain bugs/limitations", parse_hacks),
 	OPT_BOOLEAN('i',	 "ibt", &opts.ibt, "validate and annotate IBT"),
 	OPT_BOOLEAN('m',	 "mcount", &opts.mcount, "annotate mcount/fentry calls for ftrace"),
@@ -176,6 +177,7 @@ static bool opts_valid(void)
 	}
 
 	if (opts.checksum		||
+	    opts.disas			||
 	    opts.hack_jump_label	||
 	    opts.hack_noinstr		||
 	    opts.ibt			||

tools/objtool/check.c

@@ -2611,7 +2611,7 @@ static int decode_sections(struct objtool_file *file)
 	 * Must be before add_jump_destinations(), which depends on 'func'
 	 * being set for alternatives, to enable proper sibling call detection.
 	 */
-	if (validate_branch_enabled() || opts.noinstr || opts.hack_jump_label) {
+	if (validate_branch_enabled() || opts.noinstr || opts.hack_jump_label || opts.disas) {
 		if (add_special_section_alts(file))
 			return -1;
 	}
@@ -4915,14 +4915,15 @@ int check(struct objtool_file *file)
 	int ret = 0, warnings = 0;
 
 	/*
-	 * If the verbose or backtrace option is used then we need a
-	 * disassembly context to disassemble instruction or function
-	 * on warning or backtrace.
+	 * Create a disassembly context if we might disassemble any
+	 * instruction or function.
 	 */
-	if (opts.verbose || opts.backtrace || opts.trace) {
+	if (opts.verbose || opts.backtrace || opts.trace || opts.disas) {
 		disas_ctx = disas_context_create(file);
-		if (!disas_ctx)
+		if (!disas_ctx) {
+			opts.disas = false;
 			opts.trace = false;
+		}
 		objtool_disas_ctx = disas_ctx;
 	}
 
@@ -5054,11 +5055,7 @@ int check(struct objtool_file *file)
 	}
 
 out:
-	if (!ret && !warnings) {
-		free_insns(file);
-		return 0;
-	}
-
+	if (ret || warnings) {
 		if (opts.werror && warnings)
 			ret = 1;
 
@@ -5067,6 +5064,10 @@ int check(struct objtool_file *file)
 				WARN("%d warning(s) upgraded to errors", warnings);
 			disas_warned_funcs(disas_ctx);
 		}
+	}
+
+	if (opts.disas)
+		disas_funcs(disas_ctx);
 
 	if (disas_ctx) {
 		disas_context_destroy(disas_ctx);
@@ -5075,6 +5076,9 @@ int check(struct objtool_file *file)
 
 	free_insns(file);
 
+	if (!ret && !warnings)
+		return 0;
+
 	if (opts.backup && make_backup())
 		return 1;
 

tools/objtool/disas.c

@@ -4,6 +4,7 @@
  */
 
 #define _GNU_SOURCE
+#include <fnmatch.h>
 
 #include <objtool/arch.h>
 #include <objtool/check.h>
@@ -556,3 +557,29 @@ void disas_warned_funcs(struct disas_context *dctx)
 			disas_func(dctx, sym);
 	}
 }
+
+void disas_funcs(struct disas_context *dctx)
+{
+	bool disas_all = !strcmp(opts.disas, "*");
+	struct section *sec;
+	struct symbol *sym;
+
+	for_each_sec(dctx->file->elf, sec) {
+
+		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
+			continue;
+
+		sec_for_each_sym(sec, sym) {
+			/*
+			 * If the function had a warning and the verbose
+			 * option is used then the function was already
+			 * disassemble.
+			 */
+			if (opts.verbose && sym->warned)
+				continue;
+
+			if (disas_all || fnmatch(opts.disas, sym->name, 0) == 0)
+				disas_func(dctx, sym);
+		}
+	}
+}

tools/objtool/include/objtool/builtin.h

@@ -28,6 +28,7 @@ struct opts {
 	bool static_call;
 	bool uaccess;
 	int prefix;
+	const char *disas;
 
 	/* options: */
 	bool backtrace;

tools/objtool/include/objtool/disas.h

@@ -15,6 +15,7 @@ struct disassemble_info;
 struct disas_context *disas_context_create(struct objtool_file *file);
 void disas_context_destroy(struct disas_context *dctx);
 void disas_warned_funcs(struct disas_context *dctx);
+void disas_funcs(struct disas_context *dctx);
 int disas_info_init(struct disassemble_info *dinfo,
 		    int arch, int mach32, int mach64,
 		    const char *options);
@@ -40,6 +41,7 @@ static inline struct disas_context *disas_context_create(struct objtool_file *fi
 
 static inline void disas_context_destroy(struct disas_context *dctx) {}
 static inline void disas_warned_funcs(struct disas_context *dctx) {}
+static inline void disas_funcs(struct disas_context *dctx) {}
 
 static inline int disas_info_init(struct disassemble_info *dinfo,
 				  int arch, int mach32, int mach64,