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Date: Fri, 27 Sep 2019 18:58:47 +0900
From: Masahiro Yamada <yamada.masahiro@...ionext.com>
To: Jessica Yu <jeyu@...nel.org>
Cc: Matthias Maennich <maennich@...gle.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Joel Fernandes <joel@...lfernandes.org>,
Martijn Coenen <maco@...roid.com>,
Will Deacon <will.deacon@....com>,
Will Deacon <will@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] module: avoid code duplication in include/linux/export.h
On Fri, Sep 27, 2019 at 6:37 PM Masahiro Yamada
<yamada.masahiro@...ionext.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@...ionext.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
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