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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>
70 lines
1.8 KiB
Bash
Executable file
70 lines
1.8 KiB
Bash
Executable file
#!/bin/sh
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# SPDX-License-Identifier: GPL-2.0-only
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#
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# Copyright (C) 2022 Masahiro Yamada <masahiroy@kernel.org>
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# Copyright (C) 2022 Owen Rafferty <owen@owenrafferty.com>
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#
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# Exit with error if a local exported symbol is found.
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# EXPORT_SYMBOL should be used for global symbols.
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set -e
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pid=$$
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# If there is no symbol in the object, ${NM} (both GNU nm and llvm-nm) shows
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# 'no symbols' diagnostic (but exits with 0). It is harmless and hidden by
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# '2>/dev/null'. However, it suppresses real error messages as well. Add a
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# hand-crafted error message here.
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#
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# TODO:
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# Use --quiet instead of 2>/dev/null when we upgrade the minimum version of
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# binutils to 2.37, llvm to 13.0.0.
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# Then, the following line will be simpler:
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# { ${NM} --quiet ${1} || kill 0; } |
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{ ${NM} ${1} 2>/dev/null || { echo "${0}: ${NM} failed" >&2; kill $pid; } } |
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${AWK} -v "file=${1}" '
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BEGIN {
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i = 0
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}
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# Skip the line if the number of fields is less than 3.
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#
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# case 1)
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# For undefined symbols, the first field (value) is empty.
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# The outout looks like this:
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# " U _printk"
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# It is unneeded to record undefined symbols.
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#
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# case 2)
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# For Clang LTO, llvm-nm outputs a line with type t but empty name:
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# "---------------- t"
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!length($3) {
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next
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}
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# save (name, type) in the associative array
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{ symbol_types[$3]=$2 }
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# append the exported symbol to the array
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($3 ~ /^__export_symbol_.*/) {
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export_symbols[i] = $3
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sub(/^__export_symbol_/, "", export_symbols[i])
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i++
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}
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END {
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exit_code = 0
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for (j = 0; j < i; ++j) {
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name = export_symbols[j]
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# nm(3) says "If lowercase, the symbol is usually local"
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if (symbol_types[name] ~ /[a-z]/) {
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printf "%s: error: local symbol %s was exported\n",
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file, name | "cat 1>&2"
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exit_code = 1
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}
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}
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exit exit_code
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}'
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exit $?
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