[PATCH v4 2/8] allow for per-symbol configurable EXPORT_SYMBOL()

Nicolas Pitre
2016-02-29T03:48:22Z

Similar to include/generated/autoconf.h, include/generated/autoksyms.h
will contain a list of defines for each EXPORT_SYMBOL() that we want
active. The format is:

#define __KSYM_<symbol_name> 1

This list will be auto-generated with another patch. For now we only
include the preprocessor magic to automatically create or omit the
corresponding struct kernel_symbol declaration.

Given the content of include/generated/autoksyms.h may not be known in
advance, an empty file is created early on to let the build proceed.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
---
Makefile | 2 ++
include/linux/export.h | 22 ++++++++++++++++++++--
2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 6c1a3c2479..e916428cf7 100644
--- a/Makefile
+++ b/Makefile
@@ -986,6 +986,8 @@ prepare2: prepare3 outputmakefile asm-generic
prepare1: prepare2 $(version_h) include/generated/utsrelease.h \
include/config/auto.conf
$(cmd_crmodverdir)
+ $(Q)test -e include/generated/autoksyms.h || \
+ touch include/generated/autoksyms.h

archprepare: archheaders archscripts prepare1 scripts_basic

diff --git a/include/linux/export.h b/include/linux/export.h
index 96e45ea463..77afdb2a25 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -38,7 +38,7 @@ extern struct module __this_module;

#ifdef CONFIG_MODULES

-#ifndef __GENKSYMS__
+#if defined(__KERNEL__) && !defined(__GENKSYMS__)
#ifdef CONFIG_MODVERSIONS
/* Mark the CRC weak since genksyms apparently decides not to
* generate a checksums for some symbols */
@@ -53,7 +53,7 @@ extern struct module __this_module;
#endif

/* For every exported symbol, place a struct in the __ksymtab section */
-#define __EXPORT_SYMBOL(sym, sec) \
+#define ___EXPORT_SYMBOL(sym, sec) \
extern typeof(sym) sym; \
__CRC_SYMBOL(sym, sec) \
static const char __kstrtab_##sym[] \
@@ -65,6 +65,24 @@ extern struct module __this_module;
__attribute__((section("___ksymtab" sec "+" #sym), unused)) \
= { (unsigned long)&sym, __kstrtab_##sym }

+#ifdef CONFIG_TRIM_UNUSED_KSYMS
+
+#include <linux/kconfig.h>
+#include <generated/autoksyms.h>
+
+#define __EXPORT_SYMBOL(sym, sec) \
+ __cond_export_sym(sym, sec, config_enabled(__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 */
+
+#else
+#define __EXPORT_SYMBOL ___EXPORT_SYMBOL
+#endif
+
#define EXPORT_SYMBOL(sym) \
__EXPORT_SYMBOL(sym, "")

--
2.5.0