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

[Arnd Bergmann <arnd@arndb.de>]

On Tue, Aug 27, 2019 at 11:22 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
> On Tue, Aug 27, 2019 at 12:47 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > On Tue, Aug 27, 2019 at 9:23 PM Josh Poimboeuf <jpoimboe@redhat.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@gmail.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:

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