On Tue, Dec 07, 2021 at 02:37:26PM +1100, Michael Ellerman wrote: > Bill Wendling <mo...@google.com> writes: > > On Tue, Nov 30, 2021 at 10:38 AM Bill Wendling <mo...@google.com> wrote: > >> On Tue, Nov 30, 2021 at 10:17 AM Nathan Chancellor <nat...@kernel.org> > >> wrote: > >> > On Tue, Nov 30, 2021 at 10:25:43PM +1100, Michael Ellerman wrote: > >> > > Christophe Leroy <christophe.le...@csgroup.eu> writes: > >> > > > Le 29/11/2021 à 23:55, kernel test robot a écrit : > ... > >> > > >> All warnings (new ones prefixed by >>): > >> > > >> > >> > > >> In file included from arch/powerpc/kernel/asm-offsets.c:71: > >> > > >> In file included from arch/powerpc/kernel/../xmon/xmon_bpts.h:7: > >> > > >>>> arch/powerpc/include/asm/inst.h:165:20: warning: variable 'val' > >> > > >>>> is uninitialized when used here [-Wuninitialized] > >> > > >> *inst = ppc_inst(val); > >> > > >> ^~~ > >> > > >> arch/powerpc/include/asm/inst.h:53:22: note: expanded from > >> > > >> macro 'ppc_inst' > >> > > >> #define ppc_inst(x) (x) > >> > > >> ^ > >> > > >> arch/powerpc/include/asm/inst.h:155:18: note: initialize the > >> > > >> variable 'val' to silence this warning > >> > > >> unsigned int val, suffix; > >> > > >> ^ > >> > > >> = 0 > >> > > > > >> > > > I can't understand what's wrong here. > ... > >> > > > > >> > > > I see no possibility, no alternative path where val wouldn't be set. > >> > > > The > >> > > > asm clearly has *addr as an output param so it is always set. > >> > > > >> > > I guess clang can't convince itself of that? > ... > >> > > >> > It certainly looks like there is something wrong with how clang is > >> > tracking the initialization of the variable because it looks to me like > >> > val is only used in the fallthrough path, which happens after it is > >> > initialized via lwz. Perhaps something is wrong with the logic of > >> > https://reviews.llvm.org/D71314? I've added Bill to CC (LLVM issues are > >> > being migrated from Bugzilla to GitHub Issues right now so I cannot file > >> > this upstream at the moment). > >> > > >> If I remove the casts of "val" the warning doesn't appear. I suspect > >> that when I wrote that patch I forgot to remove those when checking. > >> #include "Captain_Picard_facepalm.h" > >> > >> I'll look into it. > >> > > Small retraction. It's the "*(<cast>)&val" that's the issue. (I.e. the "*&") > > I guess for now I'll just squash this in as a workaround? > > > diff --git a/arch/powerpc/include/asm/inst.h b/arch/powerpc/include/asm/inst.h > index 631436f3f5c3..5b591c51fec9 100644 > --- a/arch/powerpc/include/asm/inst.h > +++ b/arch/powerpc/include/asm/inst.h > @@ -157,6 +157,9 @@ static inline int > copy_inst_from_kernel_nofault(ppc_inst_t *inst, u32 *src) > if (unlikely(!is_kernel_addr((unsigned long)src))) > return -ERANGE;
Could we add a version check to this and a link to our bug tracker: /* https://github.com/ClangBuiltLinux/linux/issues/1521 */ #if defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 140000 > +#ifdef CONFIG_CC_IS_CLANG > + val = suffix = 0; > +#endif > __get_kernel_nofault(&val, src, u32, Efault); > if (IS_ENABLED(CONFIG_PPC64) && get_op(val) == OP_PREFIX) { > __get_kernel_nofault(&suffix, src + 1, u32, Efault); > > > > cheers
