Linux-PCI Archive on lore.kernel.org
 help / color / Atom feed
From: Nick Desaulniers <ndesaulniers@google.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-pci@vger.kernel.org, X86 ML <x86@kernel.org>
Subject: Re: [PATCH 00/22] add support for Clang LTO
Date: Tue, 7 Jul 2020 10:17:25 -0700
Message-ID: <CAKwvOd=z0n2+1voMCzC6Hft9EBdLM+6PUi9qBVTVvea_3kM91w@mail.gmail.com> (raw)
In-Reply-To: <20200707095651.422f0b22@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

On Tue, Jul 7, 2020 at 9:56 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> > On Tue, Jul 07, 2020 at 08:51:07AM -0700, Sami Tolvanen wrote:
> > > After spending some time debugging this with Nick, it looks like the
> > > error is caused by a recent optimization change in LLVM, which together
> > > with the inlining of ur_load_imm_any into jeq_imm, changes a runtime
> > > check in FIELD_FIT that would always fail, to a compile-time check that
> > > breaks the build. In jeq_imm, we have:
> > >
> > >     /* struct bpf_insn: _s32 imm */
> > >     u64 imm = insn->imm; /* sign extend */
> > >     ...
> > >     if (imm >> 32) { /* non-zero only if insn->imm is negative */
> > >             /* inlined from ur_load_imm_any */
> > >     u32 __imm = imm >> 32; /* therefore, always 0xffffffff */
> > >
> > >         /*
> > >      * __imm has a value known at compile-time, which means
> > >      * __builtin_constant_p(__imm) is true and we end up with
> > >      * essentially this in __BF_FIELD_CHECK:
> > >      */
> > >     if (__builtin_constant_p(__imm) && __imm > 255)
>
> I think FIELD_FIT() should not pass the value into __BF_FIELD_CHECK().
>
> So:
>
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 48ea093ff04c..4e035aca6f7e 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -77,7 +77,7 @@
>   */
>  #define FIELD_FIT(_mask, _val)                                         \
>         ({                                                              \
> -               __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_FIT: ");     \
> +               __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: ");     \
>                 !((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
>         })
>
> It's perfectly legal to pass a constant which does not fit, in which
> case FIELD_FIT() should just return false not break the build.
>
> Right?

I see the value of the __builtin_constant_p check; this is just a very
interesting case where rather than an integer literal appearing in the
source, the compiler is able to deduce that the parameter can only
have one value in one case, and allows __builtin_constant_p to
evaluate to true for it.

I had definitely asked Sami about the comment above FIELD_FIT:
"""
 76  * Return: true if @_val can fit inside @_mask, false if @_val is
too big.
"""
in which FIELD_FIT doesn't return false if @_val is too big and a
compile time constant. (Rather it breaks the build).

Of the 14 expansion sites of FIELD_FIT I see in mainline, it doesn't
look like any integral literals are passed, so maybe the compile time
checks of _val are of little value for FIELD_FIT.

So I think your suggested diff is the most concise fix.
-- 
Thanks,
~Nick Desaulniers

  reply index

Thread overview: 118+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24 20:31 Sami Tolvanen
2020-06-24 20:31 ` [PATCH 01/22] objtool: use sh_info to find the base for .rela sections Sami Tolvanen
2020-06-24 20:31 ` [PATCH 02/22] kbuild: add support for Clang LTO Sami Tolvanen
2020-06-24 20:53   ` Nick Desaulniers
2020-06-24 21:29     ` Sami Tolvanen
2020-06-25  2:26   ` Nathan Chancellor
2020-06-25 16:13     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 03/22] kbuild: lto: fix module versioning Sami Tolvanen
2020-06-24 20:31 ` [PATCH 04/22] kbuild: lto: fix recordmcount Sami Tolvanen
2020-06-24 21:27   ` Peter Zijlstra
2020-06-24 21:45     ` Sami Tolvanen
2020-06-25  7:45       ` Peter Zijlstra
2020-06-25 16:15         ` Sami Tolvanen
2020-06-25 20:02           ` [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool Peter Zijlstra
2020-06-25 20:54             ` Nick Desaulniers
2020-06-25 22:40             ` Sami Tolvanen
2020-06-26 11:29               ` Peter Zijlstra
2020-06-26 11:42                 ` Peter Zijlstra
2020-07-17 17:28                 ` Sami Tolvanen
2020-07-17 17:36                   ` Steven Rostedt
2020-07-17 17:47                     ` Sami Tolvanen
2020-07-17 18:05                       ` Steven Rostedt
2020-07-20 16:52                         ` Sami Tolvanen
2020-07-22 17:58                           ` Steven Rostedt
2020-07-22 18:07                             ` Sami Tolvanen
2020-07-22 17:55                 ` Steven Rostedt
2020-07-22 18:41                   ` Peter Zijlstra
2020-07-22 19:09                     ` Steven Rostedt
2020-07-22 20:03                       ` Sami Tolvanen
2020-07-22 23:56                       ` Peter Zijlstra
2020-07-23  0:06                         ` Steven Rostedt
2020-08-06 22:09                           ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 05/22] kbuild: lto: postpone objtool Sami Tolvanen
2020-06-24 21:19   ` Peter Zijlstra
2020-06-24 21:49     ` Sami Tolvanen
2020-06-25  7:47       ` Peter Zijlstra
2020-06-25 16:22         ` Sami Tolvanen
2020-06-25 18:33           ` Peter Zijlstra
2020-06-25 19:32             ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 06/22] kbuild: lto: limit inlining Sami Tolvanen
2020-06-24 21:20   ` Peter Zijlstra
2020-06-24 23:37     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 07/22] kbuild: lto: merge module sections Sami Tolvanen
2020-06-24 21:01   ` Nick Desaulniers
2020-06-24 21:31     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 08/22] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-06-24 21:13   ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 09/22] init: lto: ensure initcall ordering Sami Tolvanen
2020-06-24 20:31 ` [PATCH 10/22] init: lto: fix PREL32 relocations Sami Tolvanen
2020-06-24 20:31 ` [PATCH 11/22] pci: " Sami Tolvanen
2020-07-17 20:26   ` Bjorn Helgaas
2020-07-22 18:15     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 12/22] modpost: lto: strip .lto from module names Sami Tolvanen
2020-06-24 22:05   ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 13/22] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-06-24 20:57   ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 14/22] efi/libstub: disable LTO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 15/22] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-06-24 20:31 ` [PATCH 16/22] arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY Sami Tolvanen
2020-06-24 20:31 ` [PATCH 17/22] arm64: vdso: disable LTO Sami Tolvanen
2020-06-24 20:58   ` Nick Desaulniers
2020-06-24 21:09     ` Nick Desaulniers
2020-06-24 23:51       ` Andi Kleen
2020-06-24 21:52     ` Sami Tolvanen
2020-06-24 23:05       ` Nick Desaulniers
2020-06-24 23:39         ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 18/22] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-06-24 20:31 ` [PATCH 19/22] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 20/22] x86, ftrace: disable recordmcount for ftrace_make_nop Sami Tolvanen
2020-06-24 20:31 ` [PATCH 21/22] x86, relocs: Ignore L4_PAGE_OFFSET relocations Sami Tolvanen
2020-06-24 20:32 ` [PATCH 22/22] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-06-24 21:15 ` [PATCH 00/22] add support for Clang LTO Peter Zijlstra
2020-06-24 21:30   ` Sami Tolvanen
2020-06-25  8:27     ` Will Deacon
2020-06-24 21:31   ` Nick Desaulniers
2020-06-25  8:03     ` Peter Zijlstra
2020-06-25  8:24       ` Peter Zijlstra
2020-06-25  8:57         ` Peter Zijlstra
2020-06-30 19:19           ` Marco Elver
2020-06-30 20:12             ` Peter Zijlstra
2020-06-30 20:30               ` Paul E. McKenney
2020-07-01  9:10                 ` Peter Zijlstra
2020-07-01 14:20                   ` David Laight
2020-07-01 16:06                     ` Paul E. McKenney
2020-07-02  9:37                       ` David Laight
2020-07-02 18:00                         ` Paul E. McKenney
2020-07-01  9:41                 ` Marco Elver
2020-07-01 10:03                   ` Will Deacon
2020-07-01 11:40                   ` Peter Zijlstra
2020-07-01 14:06                     ` Paul E. McKenney
2020-07-01 15:05                       ` Peter Zijlstra
2020-07-01 16:03                         ` Paul E. McKenney
2020-07-02  8:20                           ` Peter Zijlstra
2020-07-02 17:59                             ` Paul E. McKenney
2020-07-03 13:13                               ` Peter Zijlstra
2020-07-03 13:25                                 ` Peter Zijlstra
2020-07-03 14:51                                   ` Paul E. McKenney
2020-07-03 14:42                                 ` Paul E. McKenney
2020-07-06 16:26                                   ` Paul E. McKenney
2020-07-06 18:29                                     ` Peter Zijlstra
2020-07-06 18:39                                       ` Paul E. McKenney
2020-07-06 19:40                                         ` Peter Zijlstra
2020-07-06 23:41                                           ` Paul E. McKenney
2020-06-28 16:56 ` Masahiro Yamada
2020-06-29 23:20   ` Sami Tolvanen
2020-07-07 15:51     ` Sami Tolvanen
2020-07-07 16:05       ` Sami Tolvanen
2020-07-07 16:56         ` Jakub Kicinski
2020-07-07 17:17           ` Nick Desaulniers [this message]
2020-07-07 17:30             ` Jakub Kicinski
2020-07-11 16:32 ` Paul Menzel
2020-07-12  8:59   ` Sedat Dilek
2020-07-12 18:40     ` Nathan Chancellor
2020-07-14  9:44       ` Sedat Dilek
2020-07-14 17:54         ` Nick Desaulniers
2020-07-12 23:34   ` Sami Tolvanen
2020-07-14 12:16     ` Paul Menzel
2020-07-14 12:35       ` Sedat Dilek

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAKwvOd=z0n2+1voMCzC6Hft9EBdLM+6PUi9qBVTVvea_3kM91w@mail.gmail.com' \
    --to=ndesaulniers@google.com \
    --cc=clang-built-linux@googlegroups.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=kuba@kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=masahiroy@kernel.org \
    --cc=paulmck@kernel.org \
    --cc=samitolvanen@google.com \
    --cc=will@kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-PCI Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-pci/0 linux-pci/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-pci linux-pci/ https://lore.kernel.org/linux-pci \
		linux-pci@vger.kernel.org
	public-inbox-index linux-pci

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-pci


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git