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Message-ID: <CABCJKufA-aOcsOqb1NiMQeBGm9Q-JxjoPjsuNpHh0kL4LzfO0w@mail.gmail.com> Date: Fri, 13 Nov 2020 12:24:32 -0800 From: Sami Tolvanen <samitolvanen@...gle.com> To: Josh Poimboeuf <jpoimboe@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, 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 Fri, Nov 13, 2020 at 11:54 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote: > > On Tue, Nov 10, 2020 at 10:59:55AM -0800, Sami Tolvanen wrote: > > On Tue, Nov 10, 2020 at 9:46 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote: > > > > > > On Mon, Nov 09, 2020 at 08:29:24PM -0600, Josh Poimboeuf wrote: > > > > On Mon, Nov 09, 2020 at 03:11:41PM -0800, Sami Tolvanen wrote: > > > > > CONFIG_XEN > > > > > > > > > > __switch_to_asm()+0x0: undefined stack state > > > > > xen_hypercall_set_trap_table()+0x0: <=== (sym) > > > > > > With your branch + GCC 9 I can recreate all the warnings except this > > > one. > > > > In a gcc build this warning is replaced with a different one: > > > > vmlinux.o: warning: objtool: __startup_secondary_64()+0x7: return with > > modified stack frame > > > > This just seems to depend on which function is placed right after the > > code in xen-head.S. With gcc, the disassembly looks like this: > > > > 0000000000000000 <asm_cpu_bringup_and_idle>: > > 0: e8 00 00 00 00 callq 5 <asm_cpu_bringup_and_idle+0x5> > > 1: R_X86_64_PLT32 cpu_bringup_and_idle-0x4 > > 5: e9 f6 0f 00 00 jmpq 1000 > > <xen_hypercall_set_trap_table> > > ... > > 0000000000001000 <xen_hypercall_set_trap_table>: > > ... > > ... > > 0000000000002000 <__startup_secondary_64>: > > > > With Clang+LTO, we end up with __switch_to_asm here instead of > > __startup_secondary_64. > > I still don't see this warning for some reason. Do you have CONFIG_XEN enabled? I can reproduce this on ToT master as follows: $ git rev-parse HEAD 585e5b17b92dead8a3aca4e3c9876fbca5f7e0ba $ make defconfig && \ ./scripts/config -e HYPERVISOR_GUEST -e PARAVIRT -e XEN && \ make olddefconfig && \ make -j110 ... $ ./tools/objtool/objtool check -arfld vmlinux.o 2>&1 | grep secondary vmlinux.o: warning: objtool: __startup_secondary_64()+0x2: return with modified stack frame > Is it fixed by adding cpu_bringup_and_idle() to global_noreturns[] in > tools/objtool/check.c? No, that didn't fix the warning. Here's what I tested: diff --git a/tools/objtool/check.c b/tools/objtool/check.c index c6ab44543c92..f1f65f5688cf 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -156,6 +156,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func, "machine_real_restart", "rewind_stack_do_exit", "kunit_try_catch_throw", + "cpu_bringup_and_idle", }; if (!func) Sami
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