From: Nick Desaulniers <ndesaulniers@google.com>
To: Fangrui Song <maskray@google.com>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
Borislav Petkov <bp@alien8.de>,
Nathan Chancellor <natechancellor@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Michael Matz <matz@suse.de>, Kees Cook <keescook@chromium.org>,
Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress .eh_frame sections
Date: Mon, 24 Feb 2020 13:22:10 -0800 [thread overview]
Message-ID: <CAKwvOdkoy_oaZP1fxybJu23f+V0fyrESzFO63UZenUDy+5290A@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOd=4YAj1yzncXeyDvw4ghuPCHNYU0NMGnYEDwKNozcm-uw@mail.gmail.com>
On Mon, Feb 24, 2020 at 1:17 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Mon, Feb 24, 2020 at 1:12 PM Fangrui Song <maskray@google.com> wrote:
> >
> > On 2020-02-24, Arvind Sankar wrote:
> > >On Mon, Feb 24, 2020 at 12:33:49PM -0800, Nick Desaulniers wrote:
> > >> On Sun, Feb 23, 2020 at 11:37 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >> >
> > >> > While discussing a patch to discard .eh_frame from the compressed
> > >> > vmlinux using the linker script, Fangrui Song pointed out [1] that these
> > >> > sections shouldn't exist in the first place because arch/x86/Makefile
> > >> > uses -fno-asynchronous-unwind-tables.
> > >>
> > >> Another benefit is that -fno-asynchronous-unwind-tables may help
> > >> reduce the size of .text!
> > >> https://stackoverflow.com/a/26302715/1027966
> > >
> > >Hm I don't see any change in .text size.
> > >> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > >> > index 98a81576213d..a1140c4ee478 100644
> > >> > --- a/drivers/firmware/efi/libstub/Makefile
> > >> > +++ b/drivers/firmware/efi/libstub/Makefile
> > >> > @@ -12,7 +12,8 @@ cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 \
> > >> > -mno-mmx -mno-sse -fshort-wchar \
> > >> > -Wno-pointer-sign \
> > >> > $(call cc-disable-warning, address-of-packed-member) \
> > >> > - $(call cc-disable-warning, gnu)
> > >> > + $(call cc-disable-warning, gnu) \
> > >> > + -fno-asynchronous-unwind-tables
> > >>
> > >> I think we want to add this flag a little lower, line 27 has:
> > >>
> > >> KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \
> > >>
> > >> so the `cflags-y` variable you modify in this hunk will only set
> > >> -fno-asynchronous-unwind-tables for CONFIG_X86, which I don't think is
> > >> intentional. Though when I run
> > >
> > >It is intentional -- the other case is that we're building for ARM,
> > >which only filters out the regular KBUILD_CFLAGS, so adding the flag for
> > >it should not be necessary. The cflags for ARM are constructed by
> > >manipulating KBUILD_CFLAGS. Besides it may or may not want unwind
> > >tables. 32-bit ARM appears to have an option to enable -funwind-tables.
>
> Ah, right the `subst` from `KBUILD_CFLAGS`.
> Are there other architectures that care about EFI beyond x86 and ARM? IA64?
Looks like while IA64 supports CONFIG_EFI, it doesn't support
CONFIG_EFI_STUB, which controls whether drivers/firmware/efi/libstub/
gets built or not. So that patch should be good to go.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> >
> > clang (as of today) has not implemented the
> > -funwind-tables/-fasynchronous-unwind-tables distinction as GCC does..
> > (probably because not many people care..)
>
> Ah, thanks for the clarification.
>
> >
> > >>
> > >> $ llvm-readelf -S drivers/firmware/efi/libstub/lib.a | grep eh_frame
> > >>
> > >> after doing an x86_64 defconfig, I don't get any hits. Do you observe
> > >> .eh_frame sections on any of these objects in this dir? (I'm fine
> > >> adding it to be safe, but I'm curious why I'm not seeing any
> > >> .eh_frame)
> > >>
> > >
> > >You mean before this patch, right? I see hits on every .o file in there
> > >(compiling with gcc 9.2.0).
> > >
> > >> >
> > >> > # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
> > >> > # disable the stackleak plugin
> > >> > --
> > >> > 2.24.1
> > >> >
>
>
>
> --
> Thanks,
> ~Nick Desaulniers
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2020-02-24 21:22 UTC|newest]
Thread overview: 115+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 15:02 [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage Arvind Sankar
2020-01-09 15:02 ` [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections " Arvind Sankar
2020-02-06 11:44 ` Kees Cook
2020-02-19 16:55 ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-02-22 5:08 ` [PATCH 2/2] " Nathan Chancellor
2020-02-22 6:55 ` Borislav Petkov
2020-02-22 7:02 ` Nathan Chancellor
2020-02-22 7:21 ` Fangrui Song
2020-02-22 7:42 ` Nathan Chancellor
2020-02-22 15:37 ` Arvind Sankar
2020-02-22 16:44 ` Arvind Sankar
2020-02-22 17:18 ` [PATCH] x86/boot/compressed: Fix compressed kernel linking with lld Arvind Sankar
2020-02-22 18:14 ` Nathan Chancellor
2020-02-22 18:58 ` Fangrui Song
2020-02-22 20:17 ` Arvind Sankar
2020-02-22 21:01 ` Fangrui Song
2020-02-22 23:33 ` Nick Desaulniers
2020-02-22 23:57 ` Arvind Sankar
2020-02-23 19:37 ` [PATCH 0/2] Stop generating .eh_frame sections Arvind Sankar
2020-02-24 4:15 ` Nathan Chancellor
2020-02-24 20:49 ` Nick Desaulniers
2020-02-24 21:53 ` Arvind Sankar
2020-02-24 22:01 ` Nick Desaulniers
2020-02-23 19:37 ` [PATCH 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress " Arvind Sankar
2020-02-24 20:33 ` Nick Desaulniers
2020-02-24 21:05 ` Arvind Sankar
2020-02-24 21:12 ` Fangrui Song
2020-02-24 21:17 ` Nick Desaulniers
2020-02-24 21:22 ` Nick Desaulniers [this message]
2020-02-23 19:37 ` [PATCH 2/2] arch/x86: Drop unneeded linker script discard of .eh_frame Arvind Sankar
2020-02-24 20:45 ` Nick Desaulniers
2020-02-24 21:33 ` Arvind Sankar
2020-02-24 21:58 ` Nick Desaulniers
2020-02-24 23:21 ` [PATCH v2 0/2] Stop generating .eh_frame sections Arvind Sankar
2020-02-24 23:21 ` [PATCH v2 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress " Arvind Sankar
2020-02-24 23:28 ` Nathan Chancellor
2020-02-24 23:30 ` Nick Desaulniers
2020-02-25 4:10 ` Kees Cook
2020-02-25 16:53 ` [tip: x86/boot] x86/*/Makefile: " tip-bot2 for Arvind Sankar
2020-02-24 23:21 ` [PATCH v2 2/2] arch/x86: Drop unneeded linker script discard of .eh_frame Arvind Sankar
2020-02-24 23:28 ` Nathan Chancellor
2020-02-24 23:33 ` Nick Desaulniers
2020-02-25 4:11 ` Kees Cook
2020-02-25 16:53 ` [tip: x86/boot] x86/vmlinux: " tip-bot2 for Arvind Sankar
2020-02-23 22:00 ` [PATCH] x86/boot/compressed: Fix compressed kernel linking with lld Kees Cook
2020-02-24 6:06 ` Fangrui Song
2020-02-22 17:29 ` [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections from bzImage Borislav Petkov
2020-02-22 17:53 ` Arvind Sankar
2020-02-22 7:42 ` Borislav Petkov
2020-02-22 16:22 ` Arvind Sankar
2020-02-22 23:20 ` Nick Desaulniers
2020-02-24 13:28 ` Michael Matz
2020-02-24 20:51 ` Nick Desaulniers
2020-02-24 21:28 ` Fangrui Song
2020-02-24 21:48 ` Arvind Sankar
2020-02-24 22:17 ` Fangrui Song
2020-02-24 22:43 ` Arvind Sankar
2020-02-24 22:50 ` Fangrui Song
2020-02-24 23:08 ` Arvind Sankar
2020-02-25 5:35 ` --orphan-handling=warn (was Re: [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections) " Kees Cook
2020-02-25 16:42 ` --orphan-handling=warn Arvind Sankar
2020-02-25 18:29 ` --orphan-handling=warn Arvind Sankar
2020-02-25 19:42 ` --orphan-handling=warn Kees Cook
2020-02-25 20:37 ` --orphan-handling=warn Nick Desaulniers
2020-02-25 22:02 ` --orphan-handling=warn Kees Cook
2020-02-26 1:56 ` --orphan-handling=warn Fangrui Song
2020-02-26 5:35 ` --orphan-handling=warn Kees Cook
2020-02-26 19:11 ` --orphan-handling=warn Kristen Carlson Accardi
2020-02-26 19:26 ` --orphan-handling=warn Nick Desaulniers
2020-02-24 11:37 ` [tip: x86/boot] x86/boot/compressed: Remove .eh_frame section from bzImage tip-bot2 for Arvind Sankar
2020-02-24 16:41 ` Arvind Sankar
2020-02-24 17:16 ` Borislav Petkov
2020-02-24 17:28 ` Arvind Sankar
2020-02-05 16:29 ` [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable " Arvind Sankar
2020-02-18 18:03 ` Arvind Sankar
2020-02-19 12:09 ` Borislav Petkov
2020-02-19 17:57 ` Arvind Sankar
2020-02-19 18:22 ` Borislav Petkov
2020-02-19 19:06 ` Arvind Sankar
2020-02-06 11:18 ` Kees Cook
2020-02-19 16:55 ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-04-05 15:42 ` [PATCH 1/2] " Sergey Shatunov
2020-04-05 23:18 ` Arvind Sankar
2020-04-06 0:00 ` Sergey Shatunov
2020-04-06 3:51 ` Arvind Sankar
2020-04-06 7:32 ` Ard Biesheuvel
2020-04-06 8:47 ` Borislav Petkov
2020-04-06 9:11 ` Ard Biesheuvel
2020-04-06 11:20 ` Borislav Petkov
2020-04-06 13:22 ` Arvind Sankar
2020-04-06 13:29 ` Ard Biesheuvel
2020-04-06 16:01 ` Arvind Sankar
2020-04-06 16:22 ` Ard Biesheuvel
2020-04-06 16:52 ` Arvind Sankar
2020-04-06 16:59 ` Ard Biesheuvel
2020-04-06 18:06 ` [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data Arvind Sankar
2020-04-06 18:06 ` [PATCH 2/2] efi/x86: Always relocate the kernel for EFI handover entry Arvind Sankar
2020-04-14 8:20 ` [tip: efi/urgent] " tip-bot2 for Arvind Sankar
2020-04-06 18:29 ` [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data Ard Biesheuvel
2020-04-08 7:43 ` Dave Young
2020-04-08 7:49 ` Ard Biesheuvel
2020-04-09 14:39 ` Arvind Sankar
2020-04-09 14:47 ` Ard Biesheuvel
2020-04-09 16:35 ` Arvind Sankar
2020-04-10 14:47 ` Arvind Sankar
2020-04-10 15:26 ` Ard Biesheuvel
2020-04-14 14:57 ` Daniel Kiper
2020-04-10 11:26 ` Thomas Meyer
2020-04-10 14:38 ` Arvind Sankar
2020-04-11 8:50 ` Thomas Meyer
2020-04-14 8:20 ` [tip: efi/urgent] " tip-bot2 for Arvind Sankar
2020-04-06 17:21 ` [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage Borislav Petkov
2020-04-06 8:44 ` Ard Biesheuvel
2020-04-06 12:36 ` Sergey Shatunov
2020-04-06 13:20 ` Ard Biesheuvel
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