On Tue, Aug 16, 2022 at 09:04:56AM +0200, Ard Biesheuvel wrote: > (cc Peter and Josh) > > On Mon, 15 Aug 2022 at 22:18, Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > On Mon, Aug 15, 2022 at 09:57:50PM +0200, Ard Biesheuvel wrote: > > > I'm not seeing that warning. Any config in particular beyond > > > x86_64_defconfig that you have enabled? > > > > It is my workstation's tailored config. Attached. > > > > > I'm using Debian GCC 12.1.0 btw > > > > gcc (Debian 11.2.0-19) 11.2.0 > > > > Complete thread here: > https://lore.kernel.org/all/20220815132028.732531-1-ardb@xxxxxxxxxx/ > > On Mon, 15 Aug 2022 at 22:18, Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > For some reason, objtool is not happy here: > > vmlinux.o: warning: objtool: efi_thunk_query_variable_info_nonblocking+0x1ba: unreachable instruction > > [which is the instruction right after the call to __efi_thunk64()] > > However, with the same config but without the patch (i.e., v6.0-rc1 > with nothing on top), I see: > > vmlinux.o: warning: objtool: sme_enable+0x71: unreachable instruction > > It appears that objtool is making inferences about whether or not > __efi_thunk64() returns, even though it is marked as > STACK_FRAME_NON_STANDARD. And note that I am not seeing any of these > with x86_64_defconfig, only with Boris's config (attached) STACK_FRAME_NON_STANDARD has no bearing on a call to that symbol being noreturn or not. noreturn is a bit of a pain point in that the compiler leaves no clue in the object file. Objtool has a bunch of heuristics to guess at noreturn, but the only surefire way to make things consistent is to annotate the function with __noreturn and add it to the global_noreturns[] array in tools/objtool/check.c Alternatively, if objtool guesses wrong, you can annotate the assembler with 'REACHABLE'. Josh; should we create a config file for objtool to contain many of this stuff? Then again, parsing a config file over and over and over again isn't going to make it faster :/
