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References: <20190927093603.9140-1-yamada.masahiro@socionext.com> <20190927093603.9140-5-yamada.masahiro@socionext.com>
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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Fri, 27 Sep 2019 18:58:47 +0900
Message-ID: <CAK7LNAR1ON6XjbpzDS-WXLGB49mvXkOyddHZ4mxoA-gXNrJOzQ@mail.gmail.com>
Subject: Re: [PATCH 4/7] module: avoid code duplication in include/linux/export.h
To:     Jessica Yu <jeyu@kernel.org>
Cc:     Matthias Maennich <maennich@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Martijn Coenen <maco@android.com>,
        Will Deacon <will.deacon@arm.com>,
        Will Deacon <will@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Sep 27, 2019 at 6:37 PM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> include/linux/export.h has lots of code duplication between
> EXPORT_SYMBOL and EXPORT_SYMBOL_NS.
>
> To improve the maintainability and readability, unify the
> implementation.
>
> When the symbol has no namespace, pass the empty string "" to
> the 'ns' parameter.
>
> The drawback of this change is, it grows the code size.
> When the symbol has no namespace, sym->namespace was previously
> NULL, but it is now am empty string "". So, it increases 1 byte


Just a nit.
I meant "an empty string" instead of "am empty string".


> for every no namespace EXPORT_SYMBOL.
>
> A typical kernel configuration has 10K exported symbols, so it
> increases 10KB in rough estimation.
>
> I did not come up with a good idea to refactor it without increasing
> the code size.
>
> I am not sure how big a deal it is, but at least include/linux/export.h
> looks nicer.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
>
>  include/linux/export.h | 100 +++++++++++++----------------------------
>  kernel/module.c        |   2 +-
>  2 files changed, 33 insertions(+), 69 deletions(-)
>
> diff --git a/include/linux/export.h b/include/linux/export.h
> index 621158ecd2e2..55245a405a2f 100644
> --- a/include/linux/export.h
> +++ b/include/linux/export.h
> @@ -48,45 +48,28 @@ extern struct module __this_module;
>   * absolute relocations that require runtime processing on relocatable
>   * kernels.
>   */
> -#define __KSYMTAB_ENTRY_NS(sym, sec, ns)                               \
> +#define __KSYMTAB_ENTRY(sym, sec, ns)                                  \
>         __ADDRESSABLE(sym)                                              \
>         asm("   .section \"___ksymtab" sec "+" #sym "\", \"a\"  \n"     \
>             "   .balign 4                                       \n"     \
> -           "__ksymtab_" #ns NS_SEPARATOR #sym ":               \n"     \
> +           "__ksymtab_" ns NS_SEPARATOR #sym ":                \n"     \
>             "   .long   " #sym "- .                             \n"     \
>             "   .long   __kstrtab_" #sym "- .                   \n"     \
>             "   .long   __kstrtabns_" #sym "- .                 \n"     \
>             "   .previous                                       \n")
>
> -#define __KSYMTAB_ENTRY(sym, sec)                                      \
> -       __ADDRESSABLE(sym)                                              \
> -       asm("   .section \"___ksymtab" sec "+" #sym "\", \"a\"  \n"     \
> -           "   .balign 4                                       \n"     \
> -           "__ksymtab_" #sym ":                                \n"     \
> -           "   .long   " #sym "- .                             \n"     \
> -           "   .long   __kstrtab_" #sym "- .                   \n"     \
> -           "   .long   0                                       \n"     \
> -           "   .previous                                       \n")
> -
>  struct kernel_symbol {
>         int value_offset;
>         int name_offset;
>         int namespace_offset;
>  };
>  #else
> -#define __KSYMTAB_ENTRY_NS(sym, sec, ns)                               \
> -       static const struct kernel_symbol __ksymtab_##sym##__##ns       \
> -       asm("__ksymtab_" #ns NS_SEPARATOR #sym)                         \
> -       __attribute__((section("___ksymtab" sec "+" #sym), used))       \
> -       __aligned(sizeof(void *))                                       \
> -       = { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }
> -
> -#define __KSYMTAB_ENTRY(sym, sec)                                      \
> +#define __KSYMTAB_ENTRY(sym, sec, ns)                                  \
>         static const struct kernel_symbol __ksymtab_##sym               \
> -       asm("__ksymtab_" #sym)                                          \
> +       asm("__ksymtab_" ns NS_SEPARATOR #sym)                          \
>         __attribute__((section("___ksymtab" sec "+" #sym), used))       \
>         __aligned(sizeof(void *))                                       \
> -       = { (unsigned long)&sym, __kstrtab_##sym, NULL }
> +       = { (unsigned long)&sym, __kstrtab_##sym, __kstrtabns_##sym }
>
>  struct kernel_symbol {
>         unsigned long value;
> @@ -97,29 +80,21 @@ struct kernel_symbol {
>
>  #ifdef __GENKSYMS__
>
> -#define ___EXPORT_SYMBOL(sym,sec)      __GENKSYMS_EXPORT_SYMBOL(sym)
> -#define ___EXPORT_SYMBOL_NS(sym,sec,ns)        __GENKSYMS_EXPORT_SYMBOL(sym)
> +#define ___EXPORT_SYMBOL(sym, sec, ns) __GENKSYMS_EXPORT_SYMBOL(sym)
>
>  #else
>
> -#define ___export_symbol_common(sym, sec)                              \
> +/* For every exported symbol, place a struct in the __ksymtab section */
> +#define ___EXPORT_SYMBOL(sym, sec, ns)                         \
>         extern typeof(sym) sym;                                         \
>         __CRC_SYMBOL(sym, sec);                                         \
>         static const char __kstrtab_##sym[]                             \
>         __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
> -       = #sym                                                          \
> -
> -/* For every exported symbol, place a struct in the __ksymtab section */
> -#define ___EXPORT_SYMBOL_NS(sym, sec, ns)                              \
> -       ___export_symbol_common(sym, sec);                              \
> +       = #sym;                                                         \
>         static const char __kstrtabns_##sym[]                           \
>         __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
> -       = #ns;                                                          \
> -       __KSYMTAB_ENTRY_NS(sym, sec, ns)
> -
> -#define ___EXPORT_SYMBOL(sym, sec)                                     \
> -       ___export_symbol_common(sym, sec);                              \
> -       __KSYMTAB_ENTRY(sym, sec)
> +       = ns;                                                           \
> +       __KSYMTAB_ENTRY(sym, sec, ns)
>
>  #endif
>
> @@ -130,8 +105,7 @@ struct kernel_symbol {
>   * be reused in other execution contexts such as the UEFI stub or the
>   * decompressor.
>   */
> -#define __EXPORT_SYMBOL_NS(sym, sec, ns)
> -#define __EXPORT_SYMBOL(sym, sec)
> +#define __EXPORT_SYMBOL(sym, sec, ns)
>
>  #elif defined(CONFIG_TRIM_UNUSED_KSYMS)
>
> @@ -147,48 +121,38 @@ struct kernel_symbol {
>  #define __ksym_marker(sym)     \
>         static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
>
> -#define __EXPORT_SYMBOL(sym, sec)                              \
> +#define __EXPORT_SYMBOL(sym, sec, ns)                          \
>         __ksym_marker(sym);                                     \
> -       __cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
> -#define __cond_export_sym(sym, sec, conf)                      \
> -       ___cond_export_sym(sym, sec, conf)
> -#define ___cond_export_sym(sym, sec, enabled)                  \
> -       __cond_export_sym_##enabled(sym, sec)
> -#define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec)
> -#define __cond_export_sym_0(sym, sec) /* nothing */
> -
> -#define __EXPORT_SYMBOL_NS(sym, sec, ns)                               \
> -       __ksym_marker(sym);                                             \
> -       __cond_export_ns_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
> -#define __cond_export_ns_sym(sym, sec, ns, conf)                       \
> -       ___cond_export_ns_sym(sym, sec, ns, conf)
> -#define ___cond_export_ns_sym(sym, sec, ns, enabled)                   \
> -       __cond_export_ns_sym_##enabled(sym, sec, ns)
> -#define __cond_export_ns_sym_1(sym, sec, ns) ___EXPORT_SYMBOL_NS(sym, sec, ns)
> -#define __cond_export_ns_sym_0(sym, sec, ns) /* nothing */
> +       __cond_export_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
> +#define __cond_export_sym(sym, sec, ns, conf)                  \
> +       ___cond_export_sym(sym, sec, ns, conf)
> +#define ___cond_export_sym(sym, sec, ns, enabled)              \
> +       __cond_export_sym_##enabled(sym, sec, ns)
> +#define __cond_export_sym_1(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
> +#define __cond_export_sym_0(sym, sec, ns) /* nothing */
>
>  #else
>
> -#define __EXPORT_SYMBOL_NS(sym,sec,ns) ___EXPORT_SYMBOL_NS(sym,sec,ns)
> -#define __EXPORT_SYMBOL(sym,sec)       ___EXPORT_SYMBOL(sym,sec)
> +#define __EXPORT_SYMBOL(sym, sec, ns)  ___EXPORT_SYMBOL(sym, sec, ns)
>
>  #endif /* CONFIG_MODULES */
>
>  #ifdef DEFAULT_SYMBOL_NAMESPACE
> -#undef __EXPORT_SYMBOL
> -#define __EXPORT_SYMBOL(sym, sec)                              \
> -       __EXPORT_SYMBOL_NS(sym, sec, DEFAULT_SYMBOL_NAMESPACE)
> +#include <linux/stringify.h>
> +#define _EXPORT_SYMBOL(sym, sec)       __EXPORT_SYMBOL(sym, sec, __stringify(DEFAULT_SYMBOL_NAMESPACE))
> +#else
> +#define _EXPORT_SYMBOL(sym, sec)       __EXPORT_SYMBOL(sym, sec, "")
>  #endif
>
> -#define EXPORT_SYMBOL(sym)             __EXPORT_SYMBOL(sym, "")
> -#define EXPORT_SYMBOL_GPL(sym)         __EXPORT_SYMBOL(sym, "_gpl")
> -#define EXPORT_SYMBOL_GPL_FUTURE(sym)  __EXPORT_SYMBOL(sym, "_gpl_future")
> -#define EXPORT_SYMBOL_NS(sym, ns)      __EXPORT_SYMBOL_NS(sym, "", ns)
> -#define EXPORT_SYMBOL_NS_GPL(sym, ns)  __EXPORT_SYMBOL_NS(sym, "_gpl", ns)
> +#define EXPORT_SYMBOL(sym)             _EXPORT_SYMBOL(sym, "")
> +#define EXPORT_SYMBOL_GPL(sym)         _EXPORT_SYMBOL(sym, "_gpl")
> +#define EXPORT_SYMBOL_GPL_FUTURE(sym)  _EXPORT_SYMBOL(sym, "_gpl_future")
> +#define EXPORT_SYMBOL_NS(sym, ns)      __EXPORT_SYMBOL(sym, "", #ns)
> +#define EXPORT_SYMBOL_NS_GPL(sym, ns)  __EXPORT_SYMBOL(sym, "_gpl", #ns)
>
>  #ifdef CONFIG_UNUSED_SYMBOLS
> -#define EXPORT_UNUSED_SYMBOL(sym)      __EXPORT_SYMBOL(sym, "_unused")
> -#define EXPORT_UNUSED_SYMBOL_GPL(sym)  __EXPORT_SYMBOL(sym, "_unused_gpl")
> +#define EXPORT_UNUSED_SYMBOL(sym)      _EXPORT_SYMBOL(sym, "_unused")
> +#define EXPORT_UNUSED_SYMBOL_GPL(sym)  _EXPORT_SYMBOL(sym, "_unused_gpl")
>  #else
>  #define EXPORT_UNUSED_SYMBOL(sym)
>  #define EXPORT_UNUSED_SYMBOL_GPL(sym)
> diff --git a/kernel/module.c b/kernel/module.c
> index 32873bcce738..73f69ff86db5 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1399,7 +1399,7 @@ static int verify_namespace_is_imported(const struct load_info *info,
>         char *imported_namespace;
>
>         namespace = kernel_symbol_namespace(sym);
> -       if (namespace) {
> +       if (namespace && namespace[0]) {
>                 imported_namespace = get_modinfo(info, "import_ns");
>                 while (imported_namespace) {
>                         if (strcmp(namespace, imported_namespace) == 0)
> --
> 2.17.1
>


-- 
Best Regards
Masahiro Yamada