From ddb5cdbafaaad6b99d7007ae1740403124502d03 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Mon, 12 Jun 2023 00:50:52 +0900 Subject: kbuild: generate KSYMTAB entries by modpost Commit 7b4537199a4a ("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. Commit 22823ab419d8 ("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 and 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. Commit 8651ec01daed ("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. and will remain as a wrapper of for a while. They will be removed after #include directives are all replaced with #include . [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 Reviewed-by: Nick Desaulniers --- include/linux/export-internal.h | 49 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) (limited to 'include/linux/export-internal.h') diff --git a/include/linux/export-internal.h b/include/linux/export-internal.h index fe7e6ba918f1..1c849db953a5 100644 --- a/include/linux/export-internal.h +++ b/include/linux/export-internal.h @@ -10,6 +10,55 @@ #include #include +#if defined(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS) +/* + * relative reference: this reduces the size by half on 64-bit architectures, + * and eliminates the need for absolute relocations that require runtime + * processing on relocatable kernels. + */ +#define __KSYM_REF(sym) ".long " #sym "- ." +#elif defined(CONFIG_64BIT) +#define __KSYM_REF(sym) ".quad " #sym +#else +#define __KSYM_REF(sym) ".long " #sym +#endif + +/* + * For every exported symbol, do the following: + * + * - Put the name of the symbol and namespace (empty string "" for none) in + * __ksymtab_strings. + * - Place a struct kernel_symbol entry in the __ksymtab section. + * + * Note on .section use: we specify progbits since usage of the "M" (SHF_MERGE) + * section flag requires it. Use '%progbits' instead of '@progbits' since the + * former apparently works on all arches according to the binutils source. + */ +#define __KSYMTAB(name, sym, sec, ns) \ + asm(" .section \"__ksymtab_strings\",\"aMS\",%progbits,1" "\n" \ + "__kstrtab_" #name ":" "\n" \ + " .asciz \"" #name "\"" "\n" \ + "__kstrtabns_" #name ":" "\n" \ + " .asciz \"" ns "\"" "\n" \ + " .previous" "\n" \ + " .section \"___ksymtab" sec "+" #name "\", \"a\"" "\n" \ + " .balign 4" "\n" \ + "__ksymtab_" #name ":" "\n" \ + __KSYM_REF(sym) "\n" \ + __KSYM_REF(__kstrtab_ ##name) "\n" \ + __KSYM_REF(__kstrtabns_ ##name) "\n" \ + " .previous" "\n" \ + ) + +#ifdef CONFIG_IA64 +#define KSYM_FUNC(name) @fptr(name) +#else +#define KSYM_FUNC(name) name +#endif + +#define KSYMTAB_FUNC(name, sec, ns) __KSYMTAB(name, KSYM_FUNC(name), sec, ns) +#define KSYMTAB_DATA(name, sec, ns) __KSYMTAB(name, name, sec, ns) + #define SYMBOL_CRC(sym, crc, sec) \ asm(".section \"___kcrctab" sec "+" #sym "\",\"a\"" "\n" \ "__crc_" #sym ":" "\n" \ -- cgit v1.2.3