From: "Fāng-ruì Sòng" <maskray@google.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
clang-built-linux@googlegroups.com,
Kees Cook <keescook@chromium.org>,
stable@vger.kernel.org, Jian Cai <jiancai@google.com>,
Luis Lozano <llozano@google.com>,
Manoj Gupta <manojgupta@google.com>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vmlinux.lds: consider .text.{hot|unlikely}.* part of .text too
Date: Wed, 17 Jun 2020 14:27:05 -0700 [thread overview]
Message-ID: <20200617212705.tq2q6bi446gydymo@google.com> (raw)
In-Reply-To: <20200617210613.95432-1-ndesaulniers@google.com>
On 2020-06-17, Nick Desaulniers wrote:
>ld.bfd's internal linker script considers .text.hot AND .text.hot.* to
>be part of .text, as well as .text.unlikely and .text.unlikely.*.
>ld.lld will produce .text.hot.*/.text.unlikely.* sections.
Correction to this sentence. lld is not relevant here.
-ffunction-sections combined with profile-guided optimization can
produce .text.hot.* .text.unlikely.* sections. Newer clang may produce
.text.hot. .text.unlikely. (without suffix, but with a trailing dot)
when -fno-unique-section-names is specified, as an optimization to make
.strtab smaller.
We've already seen that GCC can place main in .text.startup without
-ffunction-sections. There may be other non -ffunction-sections cases
for .text.hot.* or .text.unlikely.*. So it is definitely a good idea to
be more specific even if we don't care about -ffunction-sections for
now.
>Make sure to group these together. Otherwise these orphan sections may
>be placed outside of the the _stext/_etext boundaries.
>
>Cc: stable@vger.kernel.org
>Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=add44f8d5c5c05e08b11e033127a744d61c26aee
>Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=1de778ed23ce7492c523d5850c6c6dbb34152655
>Link: https://reviews.llvm.org/D79600
>Reported-by: Jian Cai <jiancai@google.com>
>Debugged-by: Luis Lozano <llozano@google.com>
>Suggested-by: Fāng-ruì Sòng <maskray@google.com>
>Tested-by: Luis Lozano <llozano@google.com>
>Tested-by: Manoj Gupta <manojgupta@google.com>
>Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>---
> include/asm-generic/vmlinux.lds.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
>index d7c7c7f36c4a..fe5aaef169e3 100644
>--- a/include/asm-generic/vmlinux.lds.h
>+++ b/include/asm-generic/vmlinux.lds.h
>@@ -560,7 +560,9 @@
> */
> #define TEXT_TEXT \
> ALIGN_FUNCTION(); \
>- *(.text.hot TEXT_MAIN .text.fixup .text.unlikely) \
>+ *(.text.hot .text.hot.*) \
>+ *(TEXT_MAIN .text.fixup) \
>+ *(.text.unlikely .text.unlikely.*) \
> NOINSTR_TEXT \
> *(.text..refcount) \
> *(.ref.text) \
>--
>2.27.0.290.gba653c62da-goog
>
next prev parent reply other threads:[~2020-06-17 21:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-17 21:06 [PATCH] vmlinux.lds: consider .text.{hot|unlikely}.* part of .text too Nick Desaulniers
2020-06-17 21:27 ` Fāng-ruì Sòng [this message]
2020-06-22 23:04 ` Nick Desaulniers
2020-06-22 23:15 ` Fāng-ruì Sòng
2020-06-25 18:47 ` [PATCH v2] vmlinux.lds: add PGO and AutoFDO input sections Nick Desaulniers
2020-07-01 21:54 ` Nick Desaulniers
2020-07-02 8:19 ` Arnd Bergmann
2020-07-02 15:57 ` Kees Cook
2020-07-08 23:13 ` Nick Desaulniers
2020-07-09 5:43 ` Kees Cook
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