From: Kees Cook <keescook@chromium.org>
To: Alexander Lobakin <alobakin@pm.me>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Nathan Chancellor <natechancellor@gmail.com>,
Fangrui Song <maskray@google.com>,
Jiaxun Yang <jiaxun.yang@flygoat.com>,
Alex Smith <alex.smith@imgtec.com>,
Ralf Baechle <ralf@linux-mips.org>,
Markos Chandras <markos.chandras@imgtec.com>,
linux-mips@vger.kernel.org, stable@vger.kernel.org,
linux-kernel@vger.kernel.org,
Sami Tolvanen <samitolvanen@google.com>
Subject: Re: [PATCH v2 mips-next 2/4] MIPS: vmlinux.lds.S: add ".gnu.attributes" to DISCARDS
Date: Wed, 6 Jan 2021 15:26:18 -0800 [thread overview]
Message-ID: <202101061518.67B9E0205@keescook> (raw)
In-Reply-To: <20210106223606.267756-1-alobakin@pm.me>
On Wed, Jan 06, 2021 at 10:36:38PM +0000, Alexander Lobakin wrote:
> From: Kees Cook <keescook@chromium.org>
> Date: Wed, 6 Jan 2021 14:07:07 -0800
>
> > On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
> >> Discard GNU attributes at link time as kernel doesn't use it at all.
> >> Solves a dozen of the following ld warnings (one per every file):
> >>
> >> mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes'
> >> from `arch/mips/kernel/head.o' being placed in section
> >> `.gnu.attributes'
> >> mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes'
> >> from `init/main.o' being placed in section `.gnu.attributes'
> >>
> >> Misc: sort DISCARDS section entries alphabetically.
> >
> > Hmm, I wonder what is causing the appearance of .eh_frame? With help I
> > tracked down all the causes of this on x86, arm, and arm64, so that's
> > why it's not in the asm-generic DISCARDS section. I suspect this could
> > be cleaned up for mips too?
>
> I could take a look and hunt it down. Could you please give some refs on
> what were the causes and solutions for the mentioned architectures?
Sure! Here are the ones I could find again:
34b4a5c54c42 ("arm64/kernel: Remove needless Call Frame Information annotations")
6e0a66d10c5b ("arm64/build: Remove .eh_frame* sections due to unwind tables")
d1c0272bc1c0 ("x86/boot/compressed: Remove, discard, or assert for unwanted sections")
> > Similarly for .gnu.attributes. What is generating that? (Or, more
> > specifically, why is it both being generated AND discarded?)
>
> On my setup, GNU Attributes consist of MIPS FP type (soft) and
> (if I'm correct) MIPS GNU Hash tables.
Ah, right, the soft-float markings sound correct to discard, IIUC.
> By the way. I've built the kernel with LLVM stack (and found several
> subjects for more patches) and, besides '.got', also got a fistful
> of '.data..compoundliteral*' symbols (drivers/mtd/nand/spi/,
> net/ipv6/ etc). Where should they be placed (rodata, rwdata, ...)
> or they are anomalies of some kind and should be fixed somehow?
Ah yeah, I've seen this before:
https://lore.kernel.org/lkml/202010051345.2Q0cvqdM-lkp@intel.com/
https://lore.kernel.org/lkml/CAKwvOd=s53vUELe311VSjxt2_eQd+RGNCf__n+cV+R=PQ_CdXQ@mail.gmail.com/
And it looks like LTO trips over it too:
https://lore.kernel.org/lkml/20201211184633.3213045-3-samitolvanen@google.com/
So I think the correct solution is to follow Sami's patch and add it to
vmlinux.lds.h:
-#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..LPBX*
+#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..L* .data..compoundliteral*
...
-#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]*
-#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]*
+#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* .rodata..L*
+#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* .bss..compoundliteral*
Can you include a patch for this in your series?
Thanks!
--
Kees Cook
next prev parent reply other threads:[~2021-01-06 23:27 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 20:07 [PATCH v2 mips-next 0/4] MIPS: vmlinux.lds.S sections fix & cleanup Alexander Lobakin
2021-01-06 20:08 ` [PATCH v2 mips-next 1/4] MIPS: vmlinux.lds.S: add missing PAGE_ALIGNED_DATA() section Alexander Lobakin
2021-01-06 20:08 ` [PATCH v2 mips-next 2/4] MIPS: vmlinux.lds.S: add ".gnu.attributes" to DISCARDS Alexander Lobakin
2021-01-06 22:07 ` Kees Cook
2021-01-06 22:36 ` Alexander Lobakin
2021-01-06 23:26 ` Kees Cook [this message]
2021-01-07 11:59 ` Alexander Lobakin
2021-01-06 22:43 ` Fāng-ruì Sòng
2021-01-06 20:08 ` [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time Alexander Lobakin
2021-01-06 20:21 ` Fāng-ruì Sòng
2021-01-06 20:23 ` Nathan Chancellor
2021-01-06 20:28 ` Alexander Lobakin
2021-01-06 20:08 ` [PATCH v2 mips-next 4/4] MIPS: select ARCH_WANT_LD_ORPHAN_WARN Alexander Lobakin
2021-01-06 22:07 ` Kees Cook
2021-01-06 22:07 ` [PATCH v2 mips-next 1/4] MIPS: vmlinux.lds.S: add missing PAGE_ALIGNED_DATA() section Kees Cook
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