linux-kernel - [PATCH 20/29] modpost: generate vmlinux.symvers and reuse it for the second modpost

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Date:   Sun, 17 May 2020 18:48:50 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Jessica Yu <jeyu@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 20/29] modpost: generate vmlinux.symvers and reuse it for the second modpost

The full build runs modpost twice, first for vmlinux.o and second for
modules.

The first pass dumps all the vmlinux symbols into Module.symvers, but
the second pass parses vmlinux again instead of reusing the dump file,
presumably because it needs to avoid accumulating stale symbols.

Loading symbol info from a dump file is faster than parsing an ELF object.
Besides, modpost deals with various issues to parse vmlinux in the second
pass.

A solution is to make the first pass dumps symbols into a separate file,
vmlinux.symvers. The second pass reads it, and parses module .o files.
The merged symbol information is dumped into Module.symvers as before.

This makes further modpost cleanups possible.

Also, it fixes the problem of 'make vmlinux', which previously overwrote
Module.symvers, throwing away module symbols.

I slightly touched scripts/link-vmlinux.sh so that vmlinux is re-linked
when you cross this commit. Otherwise, vmlinux.symvers would not be
generated.

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

 .gitignore               |  1 +
 Makefile                 |  2 +-
 scripts/Makefile.modpost | 11 +++++++----
 scripts/link-vmlinux.sh  |  2 --
 4 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/.gitignore b/.gitignore
index 2258e906f01c..87b9dd8a163b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,6 +56,7 @@ modules.order
 /linux
 /vmlinux
 /vmlinux.32
+/vmlinux.symvers
 /vmlinux-gdb.py
 /vmlinuz
 /System.map
diff --git a/Makefile b/Makefile
index 27e8a0522a3c..43988ce4e17e 100644
--- a/Makefile
+++ b/Makefile
@@ -1405,7 +1405,7 @@ endif # CONFIG_MODULES
 # make distclean Remove editor backup files, patch leftover files and the like
 
 # Directories & files removed with 'make clean'
-CLEAN_FILES += include/ksym \
+CLEAN_FILES += include/ksym vmlinux.symvers \
 	       modules.builtin modules.builtin.modinfo modules.nsdeps
 
 # Directories & files removed with 'make mrproper'
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index d14143b30b7a..1c597999b6a0 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -43,17 +43,17 @@ __modpost:
 include include/config/auto.conf
 include scripts/Kbuild.include
 
-kernelsymfile := $(objtree)/Module.symvers
-
 MODPOST = scripts/mod/modpost								\
 	$(if $(CONFIG_MODVERSIONS),-m)							\
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
-	$(if $(KBUILD_EXTMOD),,-o $(kernelsymfile))					\
 	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
 	$(if $(KBUILD_MODPOST_WARN),-w)
 
 ifdef MODPOST_VMLINUX
 
+# modpost options for vmlinux.o
+MODPOST += -o vmlinux.symvers
+
 quiet_cmd_modpost = MODPOST vmlinux.o
       cmd_modpost = $(MODPOST) vmlinux.o
 
@@ -68,7 +68,10 @@ MODPOST += $(subst -i,-n,$(filter -i,$(MAKEFLAGS))) -s \
 	$(if $(KBUILD_NSDEPS),-d $(MODULES_NSDEPS))
 
 ifeq ($(KBUILD_EXTMOD),)
-MODPOST += $(wildcard vmlinux)
+
+# modpost options for in-kernel modules
+MODPOST += -i vmlinux.symvers -o Module.symvers
+
 else
 
 # set src + obj - they may be used in the modules's Makefile
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index d09ab4afbda4..d5af6be50b50 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -218,8 +218,6 @@ on_signals()
 }
 trap on_signals HUP INT QUIT TERM
 
-#
-#
 # Use "make V=1" to debug this script
 case "${KBUILD_VERBOSE}" in
 *1*)
-- 
2.25.1