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kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS

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include/{linux,asm-generic}/export.h defines a weak symbol, __crc_*
as a placeholder.

Genksyms writes the version CRCs into the linker script, which will be
used for filling the __crc_* symbols. The linker script format depends
on CONFIG_MODULE_REL_CRCS. If it is enabled, __crc_* holds the offset
to the reference of CRC.

It is time to get rid of this complexity.

Now that modpost parses text files (.*.cmd) to collect all the CRCs,
it can generate C code that will be linked to the vmlinux or modules.

Generate a new C file, .vmlinux.export.c, which contains the CRCs of
symbols exported by vmlinux. It is compiled and linked to vmlinux in
scripts/link-vmlinux.sh.

Put the CRCs of symbols exported by modules into the existing *.mod.c
files. No additional build step is needed for modules. As before,
*.mod.c are compiled and linked to *.ko in scripts/Makefile.modfinal.

No linker magic is used here. The new C implementation works in the
same way, whether CONFIG_RELOCATABLE is enabled or not.
CONFIG_MODULE_REL_CRCS is no longer needed.

Previously, Kbuild invoked additional $(LD) to update the CRCs in
objects, but this step is unneeded too.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
This commit is contained in:
Masahiro Yamada
2022-05-13 20:39:22 +09:00
parent f292d875d0
commit 7b4537199a
15 changed files with 108 additions and 96 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
include/asm-generic/export.h
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@@ -2,6 +2,14 @@
#ifndef __ASM_GENERIC_EXPORT_H
#define __ASM_GENERIC_EXPORT_H
/*
* This comment block is used by fixdep. Please do not remove.
*
* When CONFIG_MODVERSIONS is changed from n to y, all source files having
* EXPORT_SYMBOL variants must be re-compiled because genksyms is run as a
* side effect of the *.o build rule.
*/
#ifndef KSYM_FUNC
#define KSYM_FUNC(x) x
#endif
@@ -12,9 +20,6 @@
#else
#define KSYM_ALIGN 4
#endif
#ifndef KCRC_ALIGN
#define KCRC_ALIGN 4
#endif
.macro __put, val, name
#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
@@ -43,17 +48,6 @@ __ksymtab_\name:
__kstrtab_\name:
.asciz "\name"
.previous
#ifdef CONFIG_MODVERSIONS
.section ___kcrctab\sec+\name,"a"
.balign KCRC_ALIGN
#if defined(CONFIG_MODULE_REL_CRCS)
.long __crc_\name - .
#else
.long __crc_\name
#endif
.weak __crc_\name
.previous
#endif
#endif
.endm