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    Subject[PATCH v6 02/10] kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS
    Date
    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>
    ---

    (no changes since v5)

    Changes in v5:
    - Fix the build error when CONFIG_DEBUG_INFO_BTF=y (reported by Nathan)
    - Clean up arch/m68k/include/asm/export.h (Nick)
    - Keep gen_symversions (and will be removed by a later patch)

    Changes in v4:
    - Rename .vmlinux-symver.c to .vmlinux.export.c
    because I notice this approach is useful for further cleanups,
    not only for modversioning but also for overall EXPORT_SYMBOL.

    Changes in v3:
    - New patch

    arch/m68k/include/asm/Kbuild | 1 +
    arch/m68k/include/asm/export.h | 2 --
    arch/powerpc/Kconfig | 1 -
    arch/s390/Kconfig | 1 -
    arch/um/Kconfig | 1 -
    include/asm-generic/export.h | 22 ++++++++--------------
    include/linux/export-internal.h | 16 ++++++++++++++++
    include/linux/export.h | 30 ++++++++----------------------
    init/Kconfig | 4 ----
    kernel/module.c | 10 +---------
    scripts/Makefile.build | 27 ++++-----------------------
    scripts/genksyms/genksyms.c | 18 ++++--------------
    scripts/link-vmlinux.sh | 14 +++++++++++++-
    scripts/mod/modpost.c | 28 ++++++++++++++++++++++++----
    14 files changed, 79 insertions(+), 96 deletions(-)
    delete mode 100644 arch/m68k/include/asm/export.h
    create mode 100644 include/linux/export-internal.h

    diff --git a/arch/m68k/include/asm/Kbuild b/arch/m68k/include/asm/Kbuild
    index 0dbf9c5c6fae..1b720299deb1 100644
    --- a/arch/m68k/include/asm/Kbuild
    +++ b/arch/m68k/include/asm/Kbuild
    @@ -1,5 +1,6 @@
    # SPDX-License-Identifier: GPL-2.0
    generated-y += syscall_table.h
    +generic-y += export.h
    generic-y += extable.h
    generic-y += kvm_para.h
    generic-y += mcs_spinlock.h
    diff --git a/arch/m68k/include/asm/export.h b/arch/m68k/include/asm/export.h
    deleted file mode 100644
    index b53008b67ce1..000000000000
    --- a/arch/m68k/include/asm/export.h
    +++ /dev/null
    @@ -1,2 +0,0 @@
    -#define KCRC_ALIGN 2
    -#include <asm-generic/export.h>
    diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
    index 174edabb74fa..a4e8dd889e29 100644
    --- a/arch/powerpc/Kconfig
    +++ b/arch/powerpc/Kconfig
    @@ -566,7 +566,6 @@ config RELOCATABLE
    bool "Build a relocatable kernel"
    depends on PPC64 || (FLATMEM && (44x || FSL_BOOKE))
    select NONSTATIC_KERNEL
    - select MODULE_REL_CRCS if MODVERSIONS
    help
    This builds a kernel image that is capable of running at the
    location the kernel is loaded at. For ppc32, there is no any
    diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
    index 77b5a03de13a..aa5848004c76 100644
    --- a/arch/s390/Kconfig
    +++ b/arch/s390/Kconfig
    @@ -567,7 +567,6 @@ endchoice

    config RELOCATABLE
    bool "Build a relocatable kernel"
    - select MODULE_REL_CRCS if MODVERSIONS
    default y
    help
    This builds a kernel image that retains relocation information
    diff --git a/arch/um/Kconfig b/arch/um/Kconfig
    index 4d398b80aea8..e8983d098e73 100644
    --- a/arch/um/Kconfig
    +++ b/arch/um/Kconfig
    @@ -106,7 +106,6 @@ config LD_SCRIPT_DYN
    bool
    default y
    depends on !LD_SCRIPT_STATIC
    - select MODULE_REL_CRCS if MODVERSIONS

    config LD_SCRIPT_DYN_RPATH
    bool "set rpath in the binary" if EXPERT
    diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
    index 07a36a874dca..5e4b1f2369d2 100644
    --- a/include/asm-generic/export.h
    +++ b/include/asm-generic/export.h
    @@ -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

    diff --git a/include/linux/export-internal.h b/include/linux/export-internal.h
    new file mode 100644
    index 000000000000..77175d561058
    --- /dev/null
    +++ b/include/linux/export-internal.h
    @@ -0,0 +1,16 @@
    +/* SPDX-License-Identifier: GPL-2.0-only */
    +/*
    + * Please do not include this explicitly.
    + * This is used by C files generated by modpost.
    + */
    +
    +#ifndef __LINUX_EXPORT_INTERNAL_H__
    +#define __LINUX_EXPORT_INTERNAL_H__
    +
    +#include <linux/compiler.h>
    +#include <linux/types.h>
    +
    +#define SYMBOL_CRC(sym, crc, sec) \
    + u32 __section("___kcrctab" sec "+" #sym) __crc_##sym = crc
    +
    +#endif /* __LINUX_EXPORT_INTERNAL_H__ */
    diff --git a/include/linux/export.h b/include/linux/export.h
    index 27d848712b90..565c5ffcb26f 100644
    --- a/include/linux/export.h
    +++ b/include/linux/export.h
    @@ -11,6 +11,14 @@
    * hackers place grumpy comments in header files.
    */

    +/*
    + * 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 __ASSEMBLY__
    #ifdef MODULE
    extern struct module __this_module;
    @@ -19,26 +27,6 @@ extern struct module __this_module;
    #define THIS_MODULE ((struct module *)0)
    #endif

    -#ifdef CONFIG_MODVERSIONS
    -/* Mark the CRC weak since genksyms apparently decides not to
    - * generate a checksums for some symbols */
    -#if defined(CONFIG_MODULE_REL_CRCS)
    -#define __CRC_SYMBOL(sym, sec) \
    - asm(" .section \"___kcrctab" sec "+" #sym "\", \"a\" \n" \
    - " .weak __crc_" #sym " \n" \
    - " .long __crc_" #sym " - . \n" \
    - " .previous \n")
    -#else
    -#define __CRC_SYMBOL(sym, sec) \
    - asm(" .section \"___kcrctab" sec "+" #sym "\", \"a\" \n" \
    - " .weak __crc_" #sym " \n" \
    - " .long __crc_" #sym " \n" \
    - " .previous \n")
    -#endif
    -#else
    -#define __CRC_SYMBOL(sym, sec)
    -#endif
    -
    #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
    #include <linux/compiler.h>
    /*
    @@ -85,7 +73,6 @@ struct kernel_symbol {
    /*
    * For every exported symbol, do the following:
    *
    - * - If applicable, place a CRC entry in the __kcrctab section.
    * - 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.
    @@ -98,7 +85,6 @@ struct kernel_symbol {
    extern typeof(sym) sym; \
    extern const char __kstrtab_##sym[]; \
    extern const char __kstrtabns_##sym[]; \
    - __CRC_SYMBOL(sym, sec); \
    asm(" .section \"__ksymtab_strings\",\"aMS\",%progbits,1 \n" \
    "__kstrtab_" #sym ": \n" \
    " .asciz \"" #sym "\" \n" \
    diff --git a/init/Kconfig b/init/Kconfig
    index ddcbefe535e9..f5b14318dfcb 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -2136,10 +2136,6 @@ config ASM_MODVERSIONS
    assembly. This can be enabled only when the target architecture
    supports it.

    -config MODULE_REL_CRCS
    - bool
    - depends on MODVERSIONS
    -
    config MODULE_SRCVERSION_ALL
    bool "Source checksum for all modules"
    help
    diff --git a/kernel/module.c b/kernel/module.c
    index 6cea788fd965..c9e2342da28e 100644
    --- a/kernel/module.c
    +++ b/kernel/module.c
    @@ -1231,11 +1231,6 @@ static int try_to_force_load(struct module *mod, const char *reason)

    #ifdef CONFIG_MODVERSIONS

    -static u32 resolve_rel_crc(const s32 *crc)
    -{
    - return *(u32 *)((void *)crc + *crc);
    -}
    -
    static int check_version(const struct load_info *info,
    const char *symname,
    struct module *mod,
    @@ -1264,10 +1259,7 @@ static int check_version(const struct load_info *info,
    if (strcmp(versions[i].name, symname) != 0)
    continue;

    - if (IS_ENABLED(CONFIG_MODULE_REL_CRCS))
    - crcval = resolve_rel_crc(crc);
    - else
    - crcval = *crc;
    + crcval = *crc;
    if (versions[i].crc == crcval)
    return 1;
    pr_debug("Found checksum %X vs module %lX\n",
    diff --git a/scripts/Makefile.build b/scripts/Makefile.build
    index a1023868775f..ddd9080fc028 100644
    --- a/scripts/Makefile.build
    +++ b/scripts/Makefile.build
    @@ -128,7 +128,6 @@ $(obj)/%.i: $(src)/%.c FORCE

    genksyms = scripts/genksyms/genksyms \
    $(if $(1), -T $(2)) \
    - $(if $(CONFIG_MODULE_REL_CRCS), -R) \
    $(if $(KBUILD_PRESERVE), -p) \
    -r $(or $(wildcard $(2:.symtypes=.symref)), /dev/null)

    @@ -162,19 +161,11 @@ ifdef CONFIG_MODVERSIONS
    # o if <file>.o doesn't contain a __ksymtab version, i.e. does
    # not export symbols, it's done.
    # o otherwise, we calculate symbol versions using the good old
    -# genksyms on the preprocessed source and postprocess them in a way
    -# that they are usable as a linker script
    -# o generate .tmp_<file>.o from <file>.o using the linker to
    -# replace the unresolved symbols __crc_exported_symbol with
    -# the actual value of the checksum generated by genksyms
    -# o remove .tmp_<file>.o to <file>.o
    +# genksyms on the preprocessed source and dump them into the .cmd file.
    +# o modpost will extract versions from that file and create *.c files that will
    +# be compiled and linked to the kernel and/or modules.

    -# Generate .o.symversions files for each .o with exported symbols, and link these
    -# to the kernel and/or modules at the end.
    -
    -genksyms_format_rel_crc := [^_]*__crc_\([^ ]*\) = \.; LONG(\([^)]*\)).*
    -genksyms_format_normal := __crc_\(.*\) = \(.*\);
    -genksyms_format := $(if $(CONFIG_MODULE_REL_CRCS),$(genksyms_format_rel_crc),$(genksyms_format_normal))
    +genksyms_format := __crc_\(.*\) = \(.*\);

    gen_symversions = \
    if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then \
    @@ -188,12 +179,6 @@ gen_symversions = \

    cmd_gen_symversions_c = $(call gen_symversions,c)

    -cmd_modversions = \
    - if [ -r $@.symversions ]; then \
    - $(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ \
    - -T $@.symversions; \
    - mv -f $(@D)/.tmp_$(@F) $@; \
    - fi
    endif

    ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
    @@ -273,7 +258,6 @@ define rule_cc_o_c
    $(call cmd,checkdoc)
    $(call cmd,gen_objtooldep)
    $(call cmd,gen_symversions_c)
    - $(if $(CONFIG_LTO_CLANG),,$(call cmd,modversions))
    $(call cmd,record_mcount)
    endef

    @@ -282,7 +266,6 @@ define rule_as_o_S
    $(call cmd,gen_ksymdeps)
    $(call cmd,gen_objtooldep)
    $(call cmd,gen_symversions_S)
    - $(call cmd,modversions)
    endef

    # Built-in and composite module parts
    @@ -296,8 +279,6 @@ ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
    quiet_cmd_cc_prelink_modules = LD [M] $@
    cmd_cc_prelink_modules = \
    $(LD) $(ld_flags) -r -o $@ \
    - $(shell [ -s $(@:.prelink.o=.o.symversions) ] && \
    - echo -T $(@:.prelink.o=.o.symversions)) \
    --whole-archive $(filter-out FORCE,$^) \
    $(cmd_objtool)

    diff --git a/scripts/genksyms/genksyms.c b/scripts/genksyms/genksyms.c
    index 4827c5abe5b7..67b23cc0df0f 100644
    --- a/scripts/genksyms/genksyms.c
    +++ b/scripts/genksyms/genksyms.c
    @@ -33,7 +33,7 @@ char *cur_filename;
    int in_source_file;

    static int flag_debug, flag_dump_defs, flag_reference, flag_dump_types,
    - flag_preserve, flag_warnings, flag_rel_crcs;
    + flag_preserve, flag_warnings;

    static int errors;
    static int nsyms;
    @@ -680,11 +680,7 @@ void export_symbol(const char *name)
    if (flag_dump_defs)
    fputs(">\n", debugfile);

    - /* Used as a linker script. */
    - printf(!flag_rel_crcs ? "__crc_%s = 0x%08lx;\n" :
    - "SECTIONS { .rodata : ALIGN(4) { "
    - "__crc_%s = .; LONG(0x%08lx); } }\n",
    - name, crc);
    + printf("__crc_%s = 0x%08lx;\n", name, crc);
    }
    }

    @@ -733,7 +729,6 @@ static void genksyms_usage(void)
    " -q, --quiet Disable warnings (default)\n"
    " -h, --help Print this message\n"
    " -V, --version Print the release version\n"
    - " -R, --relative-crc Emit section relative symbol CRCs\n"
    #else /* __GNU_LIBRARY__ */
    " -s Select symbol prefix\n"
    " -d Increment the debug level (repeatable)\n"
    @@ -745,7 +740,6 @@ static void genksyms_usage(void)
    " -q Disable warnings (default)\n"
    " -h Print this message\n"
    " -V Print the release version\n"
    - " -R Emit section relative symbol CRCs\n"
    #endif /* __GNU_LIBRARY__ */
    , stderr);
    }
    @@ -766,14 +760,13 @@ int main(int argc, char **argv)
    {"preserve", 0, 0, 'p'},
    {"version", 0, 0, 'V'},
    {"help", 0, 0, 'h'},
    - {"relative-crc", 0, 0, 'R'},
    {0, 0, 0, 0}
    };

    - while ((o = getopt_long(argc, argv, "s:dwqVDr:T:phR",
    + while ((o = getopt_long(argc, argv, "s:dwqVDr:T:ph",
    &long_opts[0], NULL)) != EOF)
    #else /* __GNU_LIBRARY__ */
    - while ((o = getopt(argc, argv, "s:dwqVDr:T:phR")) != EOF)
    + while ((o = getopt(argc, argv, "s:dwqVDr:T:ph")) != EOF)
    #endif /* __GNU_LIBRARY__ */
    switch (o) {
    case 'd':
    @@ -813,9 +806,6 @@ int main(int argc, char **argv)
    case 'h':
    genksyms_usage();
    return 0;
    - case 'R':
    - flag_rel_crcs = 1;
    - break;
    default:
    genksyms_usage();
    return 1;
    diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
    index eceb3ee7ec06..7313cbd755df 100755
    --- a/scripts/link-vmlinux.sh
    +++ b/scripts/link-vmlinux.sh
    @@ -90,7 +90,6 @@ modpost_link()

    if is_enabled CONFIG_MODVERSIONS; then
    gen_symversions
    - lds="${lds} -T .tmp_symversions.lds"
    fi

    # This might take a while, so indicate that we're doing
    @@ -183,6 +182,10 @@ vmlinux_link()
    libs="${KBUILD_VMLINUX_LIBS}"
    fi

    + if is_enabled CONFIG_MODULES; then
    + objs="${objs} .vmlinux.export.o"
    + fi
    +
    if [ "${SRCARCH}" = "um" ]; then
    wl=-Wl,
    ld="${CC}"
    @@ -312,6 +315,7 @@ cleanup()
    rm -f vmlinux.o
    rm -f .vmlinux.d
    rm -f .vmlinux.objs
    + rm -f .vmlinux.export.c
    }

    # Use "make V=1" to debug this script
    @@ -363,6 +367,14 @@ info GEN modules.builtin
    tr '\0' '\n' < modules.builtin.modinfo | sed -n 's/^[[:alnum:]:_]*\.file=//p' |
    tr ' ' '\n' | uniq | sed -e 's:^:kernel/:' -e 's/$/.ko/' > modules.builtin

    +if is_enabled CONFIG_MODULES; then
    + info CC .vmlinux.export.c
    + ${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} \
    + ${KBUILD_CPPFLAGS} ${KBUILD_CFLAGS} \
    + ${KBUILD_CFLAGS_KERNEL} ${CFLAGS_KERNEL} \
    + -c -o .vmlinux.export.o .vmlinux.export.c
    +fi
    +
    btf_vmlinux_bin_o=""
    if is_enabled CONFIG_DEBUG_INFO_BTF; then
    btf_vmlinux_bin_o=.btf.vmlinux.bin.o
    diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
    index 213a130d1635..2313bdae91bf 100644
    --- a/scripts/mod/modpost.c
    +++ b/scripts/mod/modpost.c
    @@ -1042,6 +1042,7 @@ static void add_header(struct buffer *b, struct module *mod)
    buf_printf(b, "#define INCLUDE_VERMAGIC\n");
    buf_printf(b, "#include <linux/build-salt.h>\n");
    buf_printf(b, "#include <linux/elfnote-lto.h>\n");
    + buf_printf(b, "#include <linux/export-internal.h>\n");
    buf_printf(b, "#include <linux/vermagic.h>\n");
    buf_printf(b, "#include <linux/compiler.h>\n");
    buf_printf(b, "\n");
    @@ -1076,20 +1077,26 @@ static void add_header(struct buffer *b, struct module *mod)
    buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");
    }

    -static void check_symversions(struct module *mod)
    +static void add_exported_symbols(struct buffer *buf, struct module *mod)
    {
    struct symbol *sym;

    if (!modversions)
    return;

    + /* record CRCs for exported symbols */
    + buf_printf(buf, "\n");
    list_for_each_entry(sym, &mod->exported_symbols, list) {
    if (!sym->crc_valid) {
    warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"
    "Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",
    sym->name, mod->name, mod->is_vmlinux ? "" : ".ko",
    sym->name);
    + continue;
    }
    +
    + buf_printf(buf, "SYMBOL_CRC(%s, 0x%08x, \"%s\");\n",
    + sym->name, sym->crc, sym->is_gpl_only ? "_gpl" : "");
    }
    }

    @@ -1226,6 +1233,18 @@ static void write_if_changed(struct buffer *b, const char *fname)
    write_buf(b, fname);
    }

    +static void write_vmlinux_export_c_file(struct module *mod)
    +{
    + struct buffer buf = { };
    +
    + buf_printf(&buf,
    + "#include <linux/export-internal.h>\n");
    +
    + add_exported_symbols(&buf, mod);
    + write_if_changed(&buf, ".vmlinux.export.c");
    + free(buf.p);
    +}
    +
    /* do sanity checks, and generate *.mod.c file */
    static void write_mod_c_file(struct module *mod)
    {
    @@ -1237,6 +1256,7 @@ static void write_mod_c_file(struct module *mod)
    check_exports(mod);

    add_header(&buf, mod);
    + add_exported_symbols(&buf, mod);
    add_versions(&buf, mod);
    add_depends(&buf, mod);
    add_moddevtable(&buf, mod);
    @@ -1434,9 +1454,9 @@ int main(int argc, char **argv)
    if (mod->from_dump)
    continue;

    - check_symversions(mod);
    -
    - if (!mod->is_vmlinux)
    + if (mod->is_vmlinux)
    + write_vmlinux_export_c_file(mod);
    + else
    write_mod_c_file(mod);
    }

    --
    2.32.0
    \
     
     \ /
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