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From: Masahiro Yamada <masahiroy@kernel.org>
To: linux-kbuild@vger.kernel.org
Cc: Christoph Hellwig <hch@lst.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jessica Yu <jeyu@kernel.org>, Nicolas Pitre <nico@fluxnic.net>,
	Sami Tolvanen <samitolvanen@google.com>,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	Masahiro Yamada <masahiroy@kernel.org>
Subject: [PATCH 2/4] export.h: make __ksymtab_strings per-symbol section
Date: Fri, 26 Feb 2021 01:02:44 +0900	[thread overview]
Message-ID: <20210225160247.2959903-3-masahiroy@kernel.org> (raw)
In-Reply-To: <20210225160247.2959903-1-masahiroy@kernel.org>

The export symbol tables are placed on own sections (__ksymtab*+<sym>)
and sorted by SORT (an alias of SORT_BY_NAME) because the module
subsystem uses the binary search for symbol resolution.

We did not have a good reason to do so for __ksymtab_strings, but
now I have.

To make CONFIG_TRIM_UNUSED_KSYMS work in one-pass, the linker needs
to trim unused strings of symbols and namespaces. To allow per-symbol
keep/drop choice, __ksymtab_strings must be placed on own sections.
Of course, SORT is unneeded here, though.

This keeps the string unification introduced by commit ce2b617ce8cb
("export.h: reduce __ksymtab_strings string duplication by using "MS"
section flags").

For example, the empty namespaces share the same address.

  $ nm -n
  [ snip ]
  ffffffff8233b53a r __kstrtabns_IO_APIC_get_PCI_irq_vector
  ffffffff8233b53a r __kstrtabns_I_BDEV
  ffffffff8233b53a r __kstrtabns_LZ4_decompress_fast
  ffffffff8233b53a r __kstrtabns_LZ4_decompress_fast_continue
  ffffffff8233b53a r __kstrtabns_LZ4_decompress_fast_usingDict
  ffffffff8233b53a r __kstrtabns_LZ4_decompress_safe
  ffffffff8233b53a r __kstrtabns_LZ4_decompress_safe_continue
    ...

I confirmed no size change in vmlinux.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 include/asm-generic/export.h      | 2 +-
 include/asm-generic/vmlinux.lds.h | 2 +-
 include/linux/export.h            | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
index 07a36a874dca..e847f1fde367 100644
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -39,7 +39,7 @@
 __ksymtab_\name:
 	__put \val, __kstrtab_\name
 	.previous
-	.section __ksymtab_strings,"aMS",%progbits,1
+	.section __ksymtab_strings+\name,"aMS",%progbits,1
 __kstrtab_\name:
 	.asciz "\name"
 	.previous
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c54adce8f6f6..5a2b31890bb8 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -513,7 +513,7 @@
 									\
 	/* Kernel symbol table: strings */				\
         __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) {	\
-		*(__ksymtab_strings)					\
+		*(__ksymtab_strings+*)					\
 	}								\
 									\
 	/* __*init sections */						\
diff --git a/include/linux/export.h b/include/linux/export.h
index 6271a5d9c988..01e6ab19b226 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -99,7 +99,7 @@ struct kernel_symbol {
 	extern const char __kstrtab_##sym[];					\
 	extern const char __kstrtabns_##sym[];					\
 	__CRC_SYMBOL(sym, sec);							\
-	asm("	.section \"__ksymtab_strings\",\"aMS\",%progbits,1	\n"	\
+	asm("	.section \"__ksymtab_strings+" #sym "\",\"aMS\",%progbits,1\n"	\
 	    "__kstrtab_" #sym ":					\n"	\
 	    "	.asciz 	\"" #sym "\"					\n"	\
 	    "__kstrtabns_" #sym ":					\n"	\
-- 
2.27.0


  parent reply	other threads:[~2021-02-25 16:06 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-25 16:02 [PATCH 0/4] kbuild: build speed improvment of CONFIG_TRIM_UNUSED_KSYMS Masahiro Yamada
2021-02-25 16:02 ` [PATCH 1/4] kbuild: fix UNUSED_KSYMS_WHITELIST for Clang LTO Masahiro Yamada
2021-02-25 17:45   ` Sami Tolvanen
2021-02-25 19:08     ` Masahiro Yamada
2021-02-25 16:02 ` Masahiro Yamada [this message]
2021-02-25 16:02 ` [PATCH 3/4] kbuild: separate out vmlinux.lds generation Masahiro Yamada
2021-02-25 16:02 ` [PATCH 4/4] kbuild: re-implement CONFIG_TRIM_UNUSED_KSYMS to make it work in one-pass Masahiro Yamada
2021-02-25 18:46   ` kernel test robot
2021-02-25 18:46     ` kernel test robot
2021-02-25 20:06     ` Masahiro Yamada
2021-02-25 20:06       ` Masahiro Yamada
2021-02-25 21:20       ` Sami Tolvanen
2021-02-25 21:20         ` Sami Tolvanen
2021-02-26  7:04         ` Masahiro Yamada
2021-02-26  7:04           ` Masahiro Yamada
2021-02-25 18:56   ` kernel test robot
2021-02-25 18:56     ` kernel test robot
2021-02-25 17:19 ` [PATCH 0/4] kbuild: build speed improvment of CONFIG_TRIM_UNUSED_KSYMS Nicolas Pitre
2021-02-25 18:57   ` Masahiro Yamada
2021-02-25 19:24     ` Nicolas Pitre
2021-03-09  7:28       ` Masahiro Yamada
2021-03-09 16:49         ` Nicolas Pitre

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