RE: warning: objtool: fn1 uses BP as a scratch register

[Topper, Craig]

The framepointer thing may have been fixed by this  https://reviews.llvm.org/D64294 

-----Original Message-----
From: Arnd Bergmann <arnd@xxxxxxxx> 
Sent: Friday, July 19, 2019 12:44 PM
To: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>; clang-built-linux <clang-built-linux@xxxxxxxxxxxxxxxx>; Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Topper, Craig <craig.topper@xxxxxxxxx>; Simon Pilgrim <llvm-dev@xxxxxxxxxxxxx>
Subject: Re: warning: objtool: fn1 uses BP as a scratch register

On Fri, Jul 19, 2019 at 8:50 PM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> On Fri, Jul 19, 2019 at 11:44 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > On Fri, Jul 19, 2019 at 8:31 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> > Actually the reproducer may be wrong. I reduced the test case using 
> > 9.0.0-svn363902-1~exp1+0~20190620001509.2315~1.gbp76e756,
> > and this contains a link
> >
> >          testl %ebp, %ebp
> >
> > I get the same thing with clang-8, but godbolt.org shows it only 
> > with clang-8 (see https://godbolt.org/z/g1lZO0) , not with trunk.
>
> (Sorry for sending a blank email just now)
> + Craig and Simon, in case they recall this being a recent fix in
> LLVM's x86 backend.
> Sounds like this is fixing in upstream LLVM.  Guessing this could 
> result in improper unwinding w/ clang-8, but that's kind of irrelevant 
> for x86 as there's no asm goto (though we don't need CONFIG_JUMP_LABEL 
> in LTS branches :P)

Maybe you can try the attached .config file with a more recent clang build. This showed a few hundred warnings like this one for me, so if it was not a bugfix but a random change in clang-9 that changed my reproducer.

Ignoring the 'uses BP as a scratch' warnings and the reiserfs 'unreachable instruction' ones, this is what else I got with today's
linux-next:

arch/x86/events/intel/core.o: warning: objtool:
intel_pmu_nhm_workaround()+0x103: unreachable instruction
arch/x86/ia32/ia32_signal.o: warning: objtool:
ia32_setup_rt_frame()+0x151: call to memset() with UACCESS enabled
arch/x86/kernel/cpu/mtrr/generic.o: warning: objtool:
get_fixed_ranges()+0x144: unreachable instruction
arch/x86/kernel/process.o: warning: objtool: get_tsc_mode()+0x20: call without frame pointer save/setup
arch/x86/kernel/signal.o: warning: objtool: __setup_rt_frame()+0x1a0:
call to memset() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool:
x32_setup_rt_frame()+0x1da: call to memset() with UACCESS enabled
arch/x86/kernel/tsc.o: warning: objtool: sched_clock()+0x0: call without frame pointer save/setup
arch/x86/mm/fault.o: warning: objtool: do_user_addr_fault()+0x53:
unreachable instruction
drivers/ata/sata_dwc_460ex.o: warning: objtool:
sata_dwc_bmdma_start_by_tag()+0x259: can't find switch jump table
drivers/gpu/drm/amd/amdgpu/atom.o: warning: objtool: atom_op_move() falls through to next function atom_op_and()
drivers/gpu/drm/radeon/atom.o: warning: objtool: atom_op_move()+0xce:
sibling call from callable instruction with modified stack frame
drivers/gpu/drm/radeon/atom.o: warning: objtool: atom_op_move() falls through to next function atom_op_and() modified stack frame
drivers/gpu/drm/radeon/evergreen_cs.o: warning: objtool:
evergreen_cs_parse()+0xbcf: sibling call from callable instruction with modified stack frame
drivers/gpu/drm/radeon/evergreen_cs.o: warning: objtool:
evergreen_cs_parse() falls through to next function
evergreen_dma_cs_parse()
drivers/hwmon/pmbus/adm1275.o: warning: objtool:
adm1275_probe()+0x949: unreachable instruction
drivers/media/dvb-frontends/cxd2880/cxd2880_tnrdmd_dvbt2.o: warning:
objtool: x_tune_dvbt2_demod_setting()+0x92a: can't find switch jump table
drivers/pinctrl/pinctrl-ingenic.o: warning: objtool:
ingenic_pinconf_set()+0x93: sibling call from callable instruction with modified stack frame
drivers/platform/x86/intel_speed_select_if/isst_if_common.o: warning:
objtool: isst_restore_msr_local()+0x13d: unreachable instruction
drivers/platform/x86/intel_speed_select_if/isst_if_mbox_msr.o:
warning: objtool: isst_if_send_mbox_cmd()+0x80: unreachable instruction
fs/hfsplus/xattr.o: warning: objtool:
hfsplus_create_attributes_file()+0x4f7: unreachable instruction
kernel/trace/ring_buffer.o: warning: objtool:
ring_buffer_nest_end()+0x1b: call without frame pointer save/setup
kernel/trace/trace.o: warning: objtool: saved_cmdlines_stop()+0x13:
call without frame pointer save/setup
lib/iov_iter.o: warning: objtool: .altinstr_replacement+0x30: call without frame pointer save/setup
lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch()+0x25:
call to memcpy() with UACCESS enabled
lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch_v1()+0xbd:
call to __stack_chk_fail() with UACCESS enabled
lib/ubsan.o: warning: objtool: ubsan_type_mismatch_common()+0x448:
call to __stack_chk_fail() with UACCESS enabled
mm/kasan/common.o: warning: objtool: kasan_report()+0x43: call to
__stack_chk_fail() with UACCESS enabled
mm/page_alloc.o: warning: objtool: .altinstr_replacement+0x47: call without frame pointer save/setup
mm/workingset.o: warning: objtool: count_shadow_nodes()+0x126:
unreachable instruction

Any interesting ones in there?

       Arnd