On Thu 12 May 2022 01:45:06, Masahiro Yamada wrote:
> 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@xxxxxxxxxx>
> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
>
> 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 e0f9c02d9f83..6b47a8723389 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1040,6 +1040,7 @@ 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");
> @@ -1074,20 +1075,26 @@ 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" : "");
> }
> }
>
> @@ -1224,6 +1231,18 @@ 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)
> {
> @@ -1235,6 +1254,7 @@ 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);
> @@ -1432,9 +1452,9 @@ 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
Tested-by: Nicolas Schier <nicolas@xxxxxxxxx>
Reviewed-by: Nicolas Schier <nicolas@xxxxxxxxx>
