linux-kernel - Re: [PATCH v9 00/16] Add support for Clang LTO

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Message-ID: <CA+icZUVS_CbbxG-V0RZxqxcY7E__QUrVxgC1VRmTLN4wrz=E5w@mail.gmail.com>
Date:   Sun, 10 Jan 2021 00:44:54 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v9 00/16] Add support for Clang LTO

On Sat, Jan 9, 2021 at 6:06 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Sat, Jan 09, 2021 at 11:03:57AM -0600, Josh Poimboeuf wrote:
> > On Sat, Jan 09, 2021 at 05:45:47PM +0100, Sedat Dilek wrote:
> > > I tried merging with clang-cfi Git which is based on Linux v5.11-rc2+
> > > with a lot of merge conflicts.
> > >
> > > Did you try on top of cfi-10 Git tag which is based on Linux v5.10?
> > >
> > > Whatever you successfully did... Can you give me a step-by-step instruction?
> >
> > Oops, my bad.  My last three commits (which I just added) do conflict.
> > Sorry for the confusion.
> >
> > Just drop my last three commits:
> >
> > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git objtool-vmlinux
> > git checkout -B tmp FETCH_HEAD
> > git reset --hard HEAD~~~
> > git fetch https://github.com/samitolvanen/linux clang-lto
> > git rebase --onto FETCH_HEAD 79881bfc57be
>
> Last one should be:
>
> git rebase --onto FETCH_HEAD 2c85ebc57b3e
>

Hi Josh,

as said I tried your latest changes on top of Linux v5.10.6 + cfi-5.10.
This reduces the objtool-warnings in vmlinux.o from 15 down to 2.

Without your latest changes:

$ grep 'vmlinux.o: warning: objtool:'
build-log_5.10.4-3-amd64-clang11-cfi.txt | wc -l
15

$ grep 'vmlinux.o: warning: objtool:'
build-log_5.10.4-3-amd64-clang11-cfi.txt
vmlinux.o: warning: objtool: wakeup_long64()+0x61: indirect jump found
in RETPOLINE build
vmlinux.o: warning: objtool: .text+0x408a: indirect jump found in
RETPOLINE build
vmlinux.o: warning: objtool: .text+0x40c5: indirect jump found in
RETPOLINE build
vmlinux.o: warning: objtool: .head.text+0x298: indirect jump found in
RETPOLINE build
vmlinux.o: warning: objtool: __switch_to_asm()+0x0: undefined stack state
vmlinux.o: warning: objtool: .entry.text+0xf91: sibling call from
callable instruction with modified stack frame
vmlinux.o: warning: objtool: .entry.text+0x16c4: unsupported
instruction in callable function
vmlinux.o: warning: objtool: .entry.text+0x15a4: redundant CLD
vmlinux.o: warning: objtool: do_suspend_lowlevel()+0x116: sibling call
from callable instruction with modified stack frame
vmlinux.o: warning: objtool: kretprobe_trampoline()+0x49: return with
modified stack frame
vmlinux.o: warning: objtool: machine_real_restart()+0x85: unsupported
instruction in callable function
vmlinux.o: warning: objtool: __x86_retpoline_rdi()+0x0: stack state
mismatch: cfa1=7+8 cfa2=-1+0
vmlinux.o: warning: objtool: .entry.text+0x48: stack state mismatch:
cfa1=7-8 cfa2=-1+0
vmlinux.o: warning: objtool: .entry.text+0x156d: stack state mismatch:
cfa1=7-8 cfa2=-1+0
vmlinux.o: warning: objtool: .entry.text+0x15fc: stack state mismatch:
cfa1=7-8 cfa2=-1+0

With your latest changes in <jpoimboe.git#objtool-vmlinux>:

$ grep 'vmlinux.o: warning: objtool:'
build-log_5.10.6-1-amd64-clang11-cfi.txt | wc -l
2

$ grep 'vmlinux.o: warning: objtool:' build-log_5.10.6-1-amd64-clang11-cfi.txt
vmlinux.o: warning: objtool: kretprobe_trampoline()+0x49: return with
modified stack frame
vmlinux.o: warning: objtool: machine_real_restart()+0x85: unsupported
instruction in callable function

Awesome.

If you need further information, please let me know.

Regards,
- Sedat -