linux-kernel - Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

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Message-ID: <20201021212747.ofk74lugt4hhjdzg@treble>
Date:   Wed, 21 Oct 2020 16:27:47 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

On Wed, Oct 21, 2020 at 11:32:13AM +0200, Peter Zijlstra wrote:
> On Wed, Oct 21, 2020 at 10:56:06AM +0200, Peter Zijlstra wrote:
> 
> > I do not see these in particular, although I do see a lot of:
> > 
> >   "sibling call from callable instruction with modified stack frame"
> 
> defconfig-build/vmlinux.o: warning: objtool: msr_write()+0x10a: sibling call from callable instruction with modified stack frame
> defconfig-build/vmlinux.o: warning: objtool:   msr_write()+0x99: (branch)
> defconfig-build/vmlinux.o: warning: objtool:   msr_write()+0x3e: (branch)
> defconfig-build/vmlinux.o: warning: objtool:   msr_write()+0x0: <=== (sym)
> 
> $ nm defconfig-build/vmlinux.o | grep msr_write
> 0000000000043250 t msr_write
> 00000000004289c0 T msr_write
> 0000000000003056 t msr_write.cold
> 
> Below 'fixes' it. So this is also caused by duplicate symbols.

There's a new linker flag for renaming duplicates:

  https://sourceware.org/bugzilla/show_bug.cgi?id=26391

But I guess that doesn't help us now.

I don't have access to GCC 10 at the moment so I can't recreate it.
Does this fix it?

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 4e1d7460574b..aecdf25b2381 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -217,11 +217,14 @@ struct symbol *find_func_containing(struct section *sec, unsigned long offset)
 	return NULL;
 }
 
+#define for_each_possible_sym(elf, name, sym)				\
+	elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
+
 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
 {
 	struct symbol *sym;
 
-	elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
+	for_each_possible_sym(elf, name, sym)
 		if (!strcmp(sym->name, name))
 			return sym;
 
@@ -432,6 +435,8 @@ static int read_symbols(struct elf *elf)
 		list_for_each_entry(sym, &sec->symbol_list, list) {
 			char pname[MAX_NAME_LEN + 1];
 			size_t pnamelen;
+			struct symbol *psym;
+
 			if (sym->type != STT_FUNC)
 				continue;
 
@@ -454,8 +459,14 @@ static int read_symbols(struct elf *elf)
 
 			strncpy(pname, sym->name, pnamelen);
 			pname[pnamelen] = '\0';
-			pfunc = find_symbol_by_name(elf, pname);
-
+			pfunc = NULL;
+			for_each_possible_sym(elf, pname, psym) {
+				if ((!psym->cfunc || psym->cfunc == psym) &&
+				    !strcmp(psym->name, pname)) {
+					pfunc = psym;
+					break;
+				}
+			}
 			if (!pfunc) {
 				WARN("%s(): can't find parent function",
 				     sym->name);