linux-kernel - Re: objtool warning "uses BP as a scratch register" with clang-9

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Message-ID: <20190828145102.o7h3la3ofb2b4aie@treble>
Date:   Wed, 28 Aug 2019 09:51:02 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Ilie Halip <ilie.halip@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: objtool warning "uses BP as a scratch register" with clang-9

On Wed, Aug 28, 2019 at 11:00:04AM +0200, Arnd Bergmann wrote:
> On Tue, Aug 27, 2019 at 11:22 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@...glegroups.com> wrote:
> > On Tue, Aug 27, 2019 at 12:47 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > On Tue, Aug 27, 2019 at 9:23 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > > > On Tue, Aug 27, 2019 at 09:00:52PM +0200, Arnd Bergmann wrote:
> > > > > On Tue, Aug 27, 2019 at 5:00 PM Ilie Halip <ilie.halip@...il.com> wrote:
> > Thanks for the description of the issue and the reduced test case.  It
> > almost reminds me of
> > https://github.com/ClangBuiltLinux/linux/issues/612.
> >
> > I've filed https://bugs.llvm.org/show_bug.cgi?id=43128, anything I
> > should add to the bug report?
> 
> I tried the suggestion to add
> 
> diff --git a/Makefile b/Makefile
> index 1b23f95db176..97f7bc4c9b4e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -755,7 +755,7 @@ endif
> 
>  KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
>  ifdef CONFIG_FRAME_POINTER
> -KBUILD_CFLAGS  += -fno-omit-frame-pointer -fno-optimize-sibling-calls
> +KBUILD_CFLAGS  += -fno-omit-frame-pointer -fno-optimize-sibling-calls
> $(call cc-option, -mno-omit-leaf-frame-pointer)
>  else
>  # Some targets (ARM with Thumb2, for example), can't be built with frame
>  # pointers.  For those, we don't have FUNCTION_TRACER automatically
> 
> from https://bugs.llvm.org/show_bug.cgi?id=43128, this avoids all the
> "uses BP as a scratch register" warnings as well as almost all the "call without
> frame pointer save/setup" warnings I also saw.
> 
> Only a few unique objtool warnings remain now, here are the ones I
> currently see,
> along with .config files. Let me know which ones I should investigate further,
> I assume a lot of these are known issues:

None of those look necessarily familiar.  What are the remaining "known"
clang issues which were found by objtool?

If you share .o files I can look at them.

> http://paste.ubuntu.com/p/XjdDsypRxX/
> 0x5BA1B7A1:arch/x86/ia32/ia32_signal.o: warning: objtool:
> ia32_setup_rt_frame()+0x238: call to memset() with UACCESS enabled
> 0x5BA1B7A1:arch/x86/kernel/signal.o: warning: objtool:
> __setup_rt_frame()+0x5b8: call to memset() with UACCESS enabled
> 0x5BA1B7A1:mm/kasan/common.o: warning: objtool: kasan_report()+0x44:
> call to __stack_chk_fail() with UACCESS enabled
> 0x5BA1B7A1:kernel/trace/trace_selftest_dynamic.o: warning: objtool:
> __llvm_gcov_writeout()+0x13: call without frame pointer save/setup
> 0x5BA1B7A1:kernel/trace/trace_selftest_dynamic.o: warning: objtool:
> __llvm_gcov_flush()+0x0: call without frame pointer save/setup
> 0x5BA1B7A1:kernel/trace/trace_clock.o: warning: objtool:
> __llvm_gcov_writeout()+0x14: call without frame pointer save/setup
> 0x5BA1B7A1:kernel/trace/trace_clock.o: warning: objtool:
> __llvm_gcov_flush()+0x0: call without frame pointer save/setup
> 0x5BA1B7A1:kernel/trace/*: # many more of the same, all in this directory
> 0x5BA1B7A1:kernel/trace/trace_uprobe.o: warning: objtool:
> __llvm_gcov_flush()+0x0: call without frame pointer save/setup
> 
> http://paste.ubuntu.com/p/PyYNBK5Yx2/
> 0xC1CF60CC:arch/x86/ia32/ia32_signal.o: warning: objtool:
> ia32_setup_rt_frame()+0x205: call to memset() with UACCESS enabled
> 0xC1CF60CC:arch/x86/kernel/signal.o: warning: objtool:
> __setup_rt_frame()+0x597: call to memset() with UACCESS enabled
> 0xC1CF60CC:arch/x86/kernel/process.o: warning: objtool:
> play_dead()+0x3: unreachable instruction
> 0xC1CF60CC:mm/kasan/common.o: warning: objtool: kasan_report()+0x52:
> call to __stack_chk_fail() with UACCESS enabled
> 0xC1CF60CC:kernel/sched/idle.o: warning: objtool:
> switched_to_idle()+0x3: unreachable instruction
> 0xC1CF60CC:mm/madvise.o: warning: objtool: hugepage_madvise()+0x3:
> unreachable instruction
> 0xC1CF60CC:mm/hugetlb.o: warning: objtool: hugetlb_vm_op_fault()+0x3:
> unreachable instruction
> 0xC1CF60CC:kernel/exit.o: warning: objtool: abort()+0x3: unreachable instruction
> 0xC1CF60CC:fs/hugetlbfs/inode.o: warning: objtool:
> hugetlbfs_write_end()+0x3: unreachable instruction
> 0xC1CF60CC:fs/xfs/xfs_super.o: warning: objtool:
> xfs_fs_alloc_inode()+0x3: unreachable instruction
> 0xC1CF60CC:drivers/mtd/nand/raw/nand_base.o: warning: objtool:
> nand_read_oob()+0x18d4: unreachable instruction
> 
> http://paste.ubuntu.com/p/xCXyJR4Gx6/
> 0x99965895:arch/x86/ia32/ia32_signal.o: warning: objtool:
> ia32_setup_rt_frame()+0x1f5: call to memset() with UACCESS enabled
> 0x99965895:arch/x86/kernel/signal.o: warning: objtool:
> __setup_rt_frame()+0x57f: call to memset() with UACCESS enabled
> 0x99965895:drivers/pinctrl/pinctrl-ingenic.o: warning: objtool:
> ingenic_pinconf_set()+0x10d: sibling call from callable instruction
> with modified stack frame
> 
> http://paste.ubuntu.com/p/SFQXxh6zvy/
> 0x9278DEDC:drivers/media/dvb-frontends/cxd2880/cxd2880_tnrdmd_dvbt2.o:
> warning: objtool: x_tune_dvbt2_demod_setting()+0x7f6: can't find
> switch jump table
> 0x9278DEDC:net/xfrm/xfrm_output.o: warning: objtool:
> xfrm_outer_mode_output()+0x109: unreachable instruction
> 0x9278DEDC:net/xfrm/xfrm_output.o: warning: objtool:
> xfrm_outer_mode_output()+0x109: unreachable instruction
> 
> http://paste.ubuntu.com/p/9jW8yR6Tph/
> 0xE872D410:kernel/trace/trace_branch.o: warning: objtool:
> ftrace_likely_update()+0x6c: call to __stack_chk_fail() with UACCESS
> enabled
> 0xE872D410:drivers/hwmon/pmbus/adm1275.o: warning: objtool:
> adm1275_probe()+0x756: unreachable instruction
> 
> http://paste.ubuntu.com/p/qg4bxZbxwq/
> 0xA833B0C9:drivers/gpu/drm/amd/amdgpu/atom.o: warning: objtool:
> atom_op_move() falls through to next function atom_op_and()
> 0xA833B0C9:drivers/gpu/drm/i915/display/intel_combo_phy.o: warning:
> objtool: cnl_set_procmon_ref_values()+0x125: can't find switch jump
> table
> 0xA833B0C9:drivers/gpu/drm/radeon/atom.o: warning: objtool:
> atom_op_move() falls through to next function atom_op_and()
> 0xA833B0C9:drivers/gpu/drm/radeon/evergreen_cs.o: warning: objtool:
> evergreen_cs_parse() falls through to next function
> evergreen_dma_cs_parse()
> 
> http://paste.ubuntu.com/p/W3nq9bSHHZ/
> 0xFBCA4E34:drivers/gpu/drm/amd/amdgpu/atom.o: warning: objtool:
> atom_op_move() falls through to next function atom_op_and()
> 0xFBCA4E34:drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_opp_csc_v.o:
> warning: objtool: dce110_opp_v_set_csc_default()+0x2bc: can't find
> switch jump table
> 0xFBCA4E34:drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.o:
> warning: objtool: dce_mem_input_v_program_pte_vm()+0x27f: can't find
> switch jump table

-- 
Josh