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Commit7b4537199a("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS") made modpost output CRCs in the same way whether the EXPORT_SYMBOL() is placed in *.c or *.S. For further cleanups, this commit applies a similar approach to the entire data structure of EXPORT_SYMBOL(). The EXPORT_SYMBOL() compilation is split into two stages. When a source file is compiled, EXPORT_SYMBOL() will be converted into a dummy symbol in the .export_symbol section. For example, EXPORT_SYMBOL(foo); EXPORT_SYMBOL_NS_GPL(bar, BAR_NAMESPACE); will be encoded into the following assembly code: .section ".export_symbol","a" __export_symbol_foo: .asciz "" /* license */ .asciz "" /* name space */ .balign 8 .quad foo /* symbol reference */ .previous .section ".export_symbol","a" __export_symbol_bar: .asciz "GPL" /* license */ .asciz "BAR_NAMESPACE" /* name space */ .balign 8 .quad bar /* symbol reference */ .previous They are mere markers to tell modpost the name, license, and namespace of the symbols. They will be dropped from the final vmlinux and modules because the *(.export_symbol) will go into /DISCARD/ in the linker script. Then, modpost extracts all the information about EXPORT_SYMBOL() from the .export_symbol section, and generates the final C code: KSYMTAB_FUNC(foo, "", ""); KSYMTAB_FUNC(bar, "_gpl", "BAR_NAMESPACE"); KSYMTAB_FUNC() (or KSYMTAB_DATA() if it is data) is expanded to struct kernel_symbol that will be linked to the vmlinux or a module. With this change, EXPORT_SYMBOL() works in the same way for *.c and *.S files, providing the following benefits. [1] Deprecate EXPORT_DATA_SYMBOL() In the old days, EXPORT_SYMBOL() was only available in C files. To export a symbol in *.S, EXPORT_SYMBOL() was placed in a separate *.c file. arch/arm/kernel/armksyms.c is one example written in the classic manner. Commit22823ab419("EXPORT_SYMBOL() for asm") removed this limitation. Since then, EXPORT_SYMBOL() can be placed close to the symbol definition in *.S files. It was a nice improvement. However, as that commit mentioned, you need to use EXPORT_DATA_SYMBOL() for data objects on some architectures. In the new approach, modpost checks symbol's type (STT_FUNC or not), and outputs KSYMTAB_FUNC() or KSYMTAB_DATA() accordingly. There are only two users of EXPORT_DATA_SYMBOL: EXPORT_DATA_SYMBOL_GPL(empty_zero_page) (arch/ia64/kernel/head.S) EXPORT_DATA_SYMBOL(ia64_ivt) (arch/ia64/kernel/ivt.S) They are transformed as follows and output into .vmlinux.export.c KSYMTAB_DATA(empty_zero_page, "_gpl", ""); KSYMTAB_DATA(ia64_ivt, "", ""); The other EXPORT_SYMBOL users in ia64 assembly are output as KSYMTAB_FUNC(). EXPORT_DATA_SYMBOL() is now deprecated. [2] merge <linux/export.h> and <asm-generic/export.h> There are two similar header implementations: include/linux/export.h for .c files include/asm-generic/export.h for .S files Ideally, the functionality should be consistent between them, but they tend to diverge. Commit8651ec01da("module: add support for symbol namespaces.") did not support the namespace for *.S files. This commit shifts the essential implementation part to C, which supports EXPORT_SYMBOL_NS() for *.S files. <asm/export.h> and <asm-generic/export.h> will remain as a wrapper of <linux/export.h> for a while. They will be removed after #include <asm/export.h> directives are all replaced with #include <linux/export.h>. [3] Implement CONFIG_TRIM_UNUSED_KSYMS in one-pass algorithm (by a later commit) When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses the directory tree to determine which EXPORT_SYMBOL to trim. If an EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the second traverse, where some source files are recompiled with their EXPORT_SYMBOL() tuned into a no-op. We can do this better now; modpost can selectively emit KSYMTAB entries that are really used by modules. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
68 lines
2.1 KiB
C
68 lines
2.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Please do not include this explicitly.
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* This is used by C files generated by modpost.
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*/
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#ifndef __LINUX_EXPORT_INTERNAL_H__
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#define __LINUX_EXPORT_INTERNAL_H__
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#include <linux/compiler.h>
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#include <linux/types.h>
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#if defined(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)
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/*
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* relative reference: this reduces the size by half on 64-bit architectures,
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* and eliminates the need for absolute relocations that require runtime
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* processing on relocatable kernels.
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*/
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#define __KSYM_REF(sym) ".long " #sym "- ."
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#elif defined(CONFIG_64BIT)
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#define __KSYM_REF(sym) ".quad " #sym
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#else
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#define __KSYM_REF(sym) ".long " #sym
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#endif
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/*
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* For every exported symbol, do the following:
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*
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* - Put the name of the symbol and namespace (empty string "" for none) in
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* __ksymtab_strings.
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* - Place a struct kernel_symbol entry in the __ksymtab section.
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*
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* Note on .section use: we specify progbits since usage of the "M" (SHF_MERGE)
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* section flag requires it. Use '%progbits' instead of '@progbits' since the
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* former apparently works on all arches according to the binutils source.
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*/
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#define __KSYMTAB(name, sym, sec, ns) \
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asm(" .section \"__ksymtab_strings\",\"aMS\",%progbits,1" "\n" \
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"__kstrtab_" #name ":" "\n" \
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" .asciz \"" #name "\"" "\n" \
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"__kstrtabns_" #name ":" "\n" \
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" .asciz \"" ns "\"" "\n" \
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" .previous" "\n" \
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" .section \"___ksymtab" sec "+" #name "\", \"a\"" "\n" \
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" .balign 4" "\n" \
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"__ksymtab_" #name ":" "\n" \
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__KSYM_REF(sym) "\n" \
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__KSYM_REF(__kstrtab_ ##name) "\n" \
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__KSYM_REF(__kstrtabns_ ##name) "\n" \
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" .previous" "\n" \
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)
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#ifdef CONFIG_IA64
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#define KSYM_FUNC(name) @fptr(name)
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#else
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#define KSYM_FUNC(name) name
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#endif
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#define KSYMTAB_FUNC(name, sec, ns) __KSYMTAB(name, KSYM_FUNC(name), sec, ns)
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#define KSYMTAB_DATA(name, sec, ns) __KSYMTAB(name, name, sec, ns)
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#define SYMBOL_CRC(sym, crc, sec) \
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asm(".section \"___kcrctab" sec "+" #sym "\",\"a\"" "\n" \
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"__crc_" #sym ":" "\n" \
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".long " #crc "\n" \
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".previous" "\n")
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#endif /* __LINUX_EXPORT_INTERNAL_H__ */
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