linux-kernel - [PATCH v2 01/14] objtool: Tag retpoline thunk symbols

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Date:   Wed, 20 Oct 2021 12:44:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        alexei.starovoitov@...il.com, ndesaulniers@...gle.com
Subject: [PATCH v2 01/14] objtool: Tag retpoline thunk symbols

In order to avoid calling arch_is_retpoline() (which does a strcmp)
over and over on symbols, tag them once upfront.

XXX do we also want to do __fentry__ ?
XXX do we want an enum instead of a bunch of bools ?

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 tools/objtool/check.c               |   17 +++++++++++------
 tools/objtool/include/objtool/elf.h |    1 +
 2 files changed, 12 insertions(+), 6 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1077,7 +1077,7 @@ static int add_jump_destinations(struct
 		} else if (reloc->sym->type == STT_SECTION) {
 			dest_sec = reloc->sym->sec;
 			dest_off = arch_dest_reloc_offset(reloc->addend);
-		} else if (arch_is_retpoline(reloc->sym)) {
+		} else if (reloc->sym->retpoline_thunk) {
 			/*
 			 * Retpoline jumps are really dynamic jumps in
 			 * disguise, so convert them accordingly.
@@ -1218,7 +1218,7 @@ static int add_call_destinations(struct
 
 			add_call_dest(file, insn, dest, false);
 
-		} else if (arch_is_retpoline(reloc->sym)) {
+		} else if (reloc->sym->retpoline_thunk) {
 			/*
 			 * Retpoline calls are really dynamic calls in
 			 * disguise, so convert them accordingly.
@@ -1907,17 +1907,22 @@ static int read_intra_function_calls(str
 	return 0;
 }
 
-static int read_static_call_tramps(struct objtool_file *file)
+static int classify_symbols(struct objtool_file *file)
 {
 	struct section *sec;
 	struct symbol *func;
 
 	for_each_sec(file, sec) {
 		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->bind == STB_GLOBAL &&
-			    !strncmp(func->name, STATIC_CALL_TRAMP_PREFIX_STR,
+			if (func->bind != STB_GLOBAL)
+				continue;
+
+			if (!strncmp(func->name, STATIC_CALL_TRAMP_PREFIX_STR,
 				     strlen(STATIC_CALL_TRAMP_PREFIX_STR)))
 				func->static_call_tramp = true;
+
+			if (arch_is_retpoline(func))
+				func->retpoline_thunk = true;
 		}
 	}
 
@@ -1983,7 +1988,7 @@ static int decode_sections(struct objtoo
 	/*
 	 * Must be before add_{jump_call}_destination.
 	 */
-	ret = read_static_call_tramps(file);
+	ret = classify_symbols(file);
 	if (ret)
 		return ret;
 
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -56,6 +56,7 @@ struct symbol {
 	struct symbol *pfunc, *cfunc, *alias;
 	bool uaccess_safe;
 	bool static_call_tramp;
+	bool retpoline_thunk;
 	struct list_head pv_target;
 };