[v2,15/26] kbuild: record symbol versions in *.cmd files

Message ID	20220501084032.1025918-16-masahiroy@kernel.org (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-kbuild-owner@kernel.org> From: Masahiro Yamada <masahiroy@kernel.org> To: linux-kbuild@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Masahiro Yamada <masahiroy@kernel.org>, Nicolas Schier <nicolas@fjasle.eu>, Michal Marek <michal.lkml@markovi.net>, Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, llvm@lists.linux.dev Subject: [PATCH v2 15/26] kbuild: record symbol versions in *.cmd files Date: Sun, 1 May 2022 17:40:21 +0900 Message-Id: <20220501084032.1025918-16-masahiroy@kernel.org> In-Reply-To: <20220501084032.1025918-1-masahiroy@kernel.org> References: <20220501084032.1025918-1-masahiroy@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	kbuild: yet another series of cleanups (modpost and LTO) \| expand [v2,00/26] kbuild: yet another series of cleanups (modpost and LTO) [v2,01/26] modpost: use bool type where appropriate [v2,02/26] modpost: change mod->gpl_compatible to bool type [v2,03/26] modpost: import include/linux/list.h [v2,04/26] modpost: traverse modules in order [v2,05/26] modpost: add sym_add_unresolved() helper [v2,06/26] modpost: traverse unresolved symbols in order [v2,07/26] modpost: use doubly linked list for dump_lists [v2,08/26] modpost: traverse the namespace_list in order [v2,09/26] modpost: dump Module.symvers in the same order of modules.order [v2,10/26] modpost: move static EXPORT_SYMBOL check to check_exports() [v2,11/26] modpost: make multiple export error [v2,12/26] modpost: make sym_add_exported() always allocate a new symbol [v2,13/26] modpost: split new_symbol() to symbol allocation and hash table addition [v2,14/26] modpost: mitigate false-negatives for static EXPORT_SYMBOL checks [v2,15/26] kbuild: record symbol versions in .cmd files [v2,16/26] kbuild: generate a list of objects in vmlinux [v2,17/26] modpost: extract symbol versions from .cmd files [v2,18/26] modpost: generate linker script to collect symbol versions [v2,19/26] kbuild: embed symbol versions at final link of vmlinux or modules [v2,20/26] kbuild: stop merging .symversions [v2,21/26] genksyms: adjust the output format for .cmd files [v2,22/26] kbuild: do not create .prelink.o for Clang LTO or IBT [v2,23/26] kbuild: make built-in.a rule robust against too long argument error [v2,24/26] kbuild: make *.mod rule robust against too long argument error [v2,25/26] modpost: simplify the ->is_static initialization [v2,26/26] modpost: use hlist for hash table implementation

Message ID

20220501084032.1025918-16-masahiroy@kernel.org (mailing list archive)

State

New, archived

Headers

From: Masahiro Yamada <masahiroy@kernel.org>
To: linux-kbuild@vger.kernel.org
Cc: linux-kernel@vger.kernel.org,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Michal Marek <michal.lkml@markovi.net>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        llvm@lists.linux.dev
Subject: [PATCH v2 15/26] kbuild: record symbol versions in *.cmd files
Date: Sun,  1 May 2022 17:40:21 +0900
Message-Id: <20220501084032.1025918-16-masahiroy@kernel.org>
In-Reply-To: <20220501084032.1025918-1-masahiroy@kernel.org>
References: <20220501084032.1025918-1-masahiroy@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Series

kbuild: yet another series of cleanups (modpost and LTO) | expand

Commit Message

Masahiro Yamada May 1, 2022, 8:40 a.m. UTC

When CONFIG_MODVERSIONS=y, the output from genksyms is saved in
separate *.symversions files, and will be used much later when
CONFIG_LTO_CLANG=y because it is impossible to update LLVM bit code
here.

This approach is not robust because:

 - *.symversions may or may not exist. If *.symversions does not
   exist, we never know if it is missing for legitimate reason
   (i.e. no EXPORT_SYMBOL) or something bad has happened (for
   example, the user accidentally deleted it). Once it occurs,
   it is not self-healing because *.symversions is generated
   as a side effect.

 - stale (i.e. invalid) *.symversions might be picked up if an
   object is generated in a non-ordinary way, and corresponding
   *.symversions (, which was generated by old builds) just happen
   to exist.

A more robust approach is to save symbol versions in *.cmd files
because:

 - *.cmd always exists (if the object is generated by if_changed
   rule or friends). Even if the user accidentally deletes it,
   it will be regenerated in the next build.

 - *.cmd is always re-generated when the object is updated. This
   avoid stale version information being picked up.

I will remove *.symversions later.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
---

Changes in v2:
  - Fix CONFIG_MODULE_REL_CRCS=y case

 scripts/Makefile.build | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index f6a506318795..a1023868775f 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -171,10 +171,17 @@  ifdef CONFIG_MODVERSIONS
 
 # Generate .o.symversions files for each .o with exported symbols, and link these
 # to the kernel and/or modules at the end.
+
+genksyms_format_rel_crc := [^_]*__crc_\([^ ]*\) = \.; LONG(\([^)]*\)).*
+genksyms_format_normal := __crc_\(.*\) = \(.*\);
+genksyms_format := $(if $(CONFIG_MODULE_REL_CRCS),$(genksyms_format_rel_crc),$(genksyms_format_normal))
+
 gen_symversions =								\
 	if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then			\
 		$(call cmd_gensymtypes_$(1),$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
 		    > $@.symversions;						\
+		sed -n 's/$(genksyms_format)/$(pound)SYMVER \1 \2/p' $@.symversions \
+			>> $(dot-target).cmd;					\
 	else									\
 		rm -f $@.symversions;						\
 	fi

[v2,15/26] kbuild: record symbol versions in *.cmd files

Commit Message

Patch