On Wed, Jul 24, 2019 at 6:48 PM Peter Zijlstra <pet...@infradead.org> wrote: > > On Wed, Jul 24, 2019 at 04:10:40PM +0200, Peter Zijlstra wrote: > > And that most certainly should trigger... > > > > Let me gdb that objtool thing. > > --- > Subject: objtool: Improve UACCESS coverage > > A clang build reported an (obvious) double CLAC while a GCC build did > not; it turns out we only re-visit instructions if the first visit was > with AC=0. If OTOH the first visit was with AC=1, we completely ignore > any subsequent visit, even when it has AC=0. > > Fix this by using a visited mask, instead of boolean and (explicitly) > mark the AC state. > > $ ./objtool check -b --no-fp --retpoline --uaccess > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: .altinstr_replacement+0x22: redundant UACCESS disable > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: eb_copy_relocations.isra.34()+0xea: (alt) > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: .altinstr_replacement+0xffffffffffffffff: (branch) > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: eb_copy_relocations.isra.34()+0xd9: (alt) > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: eb_copy_relocations.isra.34()+0xb2: (branch) > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: eb_copy_relocations.isra.34()+0x39: (branch) > ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: > warning: objtool: eb_copy_relocations.isra.34()+0x0: <=== (func) > > Reported-by: Josh Poimboeuf <jpoim...@redhat.com> > Reported-by: Thomas Gleixner <t...@linutronix.de> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Thanks Peter Z. and Josh P.! Reported-by: Sedat Dilek <sedat.di...@gmail.com> Tested-by: Sedat Dilek <sedat.di...@gmail.com> [1] https://github.com/ClangBuiltLinux/linux/issues/617 > --- > tools/objtool/check.c | 7 ++++--- > tools/objtool/check.h | 3 ++- > 2 files changed, 6 insertions(+), 4 deletions(-) > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > index 5f26620f13f5..176f2f084060 100644 > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -1946,6 +1946,7 @@ static int validate_branch(struct objtool_file *file, > struct symbol *func, > struct alternative *alt; > struct instruction *insn, *next_insn; > struct section *sec; > + u8 visited; > int ret; > > insn = first; > @@ -1972,12 +1973,12 @@ static int validate_branch(struct objtool_file *file, > struct symbol *func, > return 1; > } > > + visited = 1 << state.uaccess; > if (insn->visited) { > if (!insn->hint && !insn_state_match(insn, &state)) > return 1; > > - /* If we were here with AC=0, but now have AC=1, go > again */ > - if (insn->state.uaccess || !state.uaccess) > + if (insn->visited & visited) > return 0; > } > > @@ -2024,7 +2025,7 @@ static int validate_branch(struct objtool_file *file, > struct symbol *func, > } else > insn->state = state; > > - insn->visited = true; > + insn->visited |= visited; > > if (!insn->ignore_alts) { > bool skip_orig = false; > diff --git a/tools/objtool/check.h b/tools/objtool/check.h > index b881fafcf55d..6d875ca6fce0 100644 > --- a/tools/objtool/check.h > +++ b/tools/objtool/check.h > @@ -33,8 +33,9 @@ struct instruction { > unsigned int len; > enum insn_type type; > unsigned long immediate; > - bool alt_group, visited, dead_end, ignore, hint, save, restore, > ignore_alts; > + bool alt_group, dead_end, ignore, hint, save, restore, ignore_alts; > bool retpoline_safe; > + u8 visited; > struct symbol *call_dest; > struct instruction *jump_dest; > struct instruction *first_jump_src;
