[PATCH] Add EXPORT_UNUSED_SYMBOL and EXPORT_UNUSED_SYMBOL_GPL

Temporarily add EXPORT_UNUSED_SYMBOL and EXPORT_UNUSED_SYMBOL_GPL.  These
will be used as a transition measure for symbols that aren't used in the
kernel and are on the way out.  When a module uses such a symbol, a warning
is printk'd at modprobe time.

The main reason for removing unused exports is size: eacho export takes
roughly between 100 and 150 bytes of kernel space in the binary.  This
patch gives users the option to immediately get this size gain via a config
option.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 150 insertions, 2 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 027285d0c26c..033ac91da07a 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -177,6 +177,16 @@ Who:	Jean Delvare <khali@linux-fr.org>
 
 ---------------------------
 
+What:   Unused EXPORT_SYMBOL/EXPORT_SYMBOL_GPL exports
+        (temporary transition config option provided until then)
+        The transition config option will also be removed at the same time.
+When:   before 2.6.19
+Why:    Unused symbols are both increasing the size of the kernel binary
+        and are often a sign of "wrong API"
+Who:    Arjan van de Ven <arjan@linux.intel.com>
+
+---------------------------
+
 What:   remove EXPORT_SYMBOL(tasklist_lock)
 When:   August 2006
 Files:  kernel/fork.c
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 9d11550b4818..db5a3732f106 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -58,6 +58,20 @@
                 VMLINUX_SYMBOL(__stop___ksymtab_gpl) = .;               \
         }                                                               \
                                                                         \
+        /* Kernel symbol table: Normal unused symbols */                \
+        __ksymtab_unused  : AT(ADDR(__ksymtab_unused) - LOAD_OFFSET) {  \
+                VMLINUX_SYMBOL(__start___ksymtab_unused) = .;           \
+                *(__ksymtab_unused)                                     \
+                VMLINUX_SYMBOL(__stop___ksymtab_unused) = .;            \
+        }                                                               \
+                                                                        \
+        /* Kernel symbol table: GPL-only unused symbols */              \
+        __ksymtab_unused_gpl : AT(ADDR(__ksymtab_unused_gpl) - LOAD_OFFSET) { \
+                VMLINUX_SYMBOL(__start___ksymtab_unused_gpl) = .;       \
+                *(__ksymtab_unused_gpl)                                 \
+                VMLINUX_SYMBOL(__stop___ksymtab_unused_gpl) = .;        \
+        }                                                               \
+                                                                        \
         /* Kernel symbol table: GPL-future-only symbols */              \
         __ksymtab_gpl_future : AT(ADDR(__ksymtab_gpl_future) - LOAD_OFFSET) { \
                 VMLINUX_SYMBOL(__start___ksymtab_gpl_future) = .;       \
@@ -79,6 +93,20 @@
                 VMLINUX_SYMBOL(__stop___kcrctab_gpl) = .;               \
         }                                                               \
                                                                         \
+        /* Kernel symbol table: Normal unused symbols */                \
+        __kcrctab_unused  : AT(ADDR(__kcrctab_unused) - LOAD_OFFSET) {  \
+                VMLINUX_SYMBOL(__start___kcrctab_unused) = .;           \
+                *(__kcrctab_unused)                                     \
+                VMLINUX_SYMBOL(__stop___kcrctab_unused) = .;            \
+        }                                                               \
+                                                                        \
+        /* Kernel symbol table: GPL-only unused symbols */              \
+        __kcrctab_unused_gpl : AT(ADDR(__kcrctab_unused_gpl) - LOAD_OFFSET) { \
+                VMLINUX_SYMBOL(__start___kcrctab_unused_gpl) = .;       \
+                *(__kcrctab_unused_gpl)                                 \
+                VMLINUX_SYMBOL(__stop___kcrctab_unused_gpl) = .;        \
+        }                                                               \
+                                                                        \
         /* Kernel symbol table: GPL-future-only symbols */              \
         __kcrctab_gpl_future : AT(ADDR(__kcrctab_gpl_future) - LOAD_OFFSET) { \
                 VMLINUX_SYMBOL(__start___kcrctab_gpl_future) = .;       \
diff --git a/include/linux/module.h b/include/linux/module.h
index 9ebbb74b7b72..9e9dc7c24d95 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -203,6 +203,15 @@ void *__symbol_get_gpl(const char *symbol);
 #define EXPORT_SYMBOL_GPL_FUTURE(sym)                           \
         __EXPORT_SYMBOL(sym, "_gpl_future")
 
+
+#ifdef CONFIG_UNUSED_SYMBOLS
+#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)
+#endif
+
 #endif
 
 struct module_ref
@@ -261,6 +270,15 @@ struct module
         unsigned int num_gpl_syms;
         const unsigned long *gpl_crcs;
 
+        /* unused exported symbols. */
+        const struct kernel_symbol *unused_syms;
+        unsigned int num_unused_syms;
+        const unsigned long *unused_crcs;
+        /* GPL-only, unused exported symbols. */
+        const struct kernel_symbol *unused_gpl_syms;
+        unsigned int num_unused_gpl_syms;
+        const unsigned long *unused_gpl_crcs;
+
         /* symbols that will be GPL-only in the near future. */
         const struct kernel_symbol *gpl_future_syms;
         unsigned int num_gpl_future_syms;
@@ -456,6 +474,8 @@ void module_remove_driver(struct device_driver *);
 #define EXPORT_SYMBOL(sym)
 #define EXPORT_SYMBOL_GPL(sym)
 #define EXPORT_SYMBOL_GPL_FUTURE(sym)
+#define EXPORT_UNUSED_SYMBOL(sym)
+#define EXPORT_UNUSED_SYMBOL_GPL(sym)
 
 /* Given an address, look for it in the exception tables. */
 static inline const struct exception_table_entry *
diff --git a/kernel/module.c b/kernel/module.c
index 10e5b872adf6..03b738172a8c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1,4 +1,4 @@
-/* Rewritten by Rusty Russell, on the backs of many others...
+/*
    Copyright (C) 2002 Richard Henderson
    Copyright (C) 2001 Rusty Russell, 2002 Rusty Russell IBM.
 
@@ -122,9 +122,17 @@ extern const struct kernel_symbol __start___ksymtab_gpl[];
 extern const struct kernel_symbol __stop___ksymtab_gpl[];
 extern const struct kernel_symbol __start___ksymtab_gpl_future[];
 extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
+extern const struct kernel_symbol __start___ksymtab_unused[];
+extern const struct kernel_symbol __stop___ksymtab_unused[];
+extern const struct kernel_symbol __start___ksymtab_unused_gpl[];
+extern const struct kernel_symbol __stop___ksymtab_unused_gpl[];
+extern const struct kernel_symbol __start___ksymtab_gpl_future[];
+extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
 extern const unsigned long __start___kcrctab[];
 extern const unsigned long __start___kcrctab_gpl[];
 extern const unsigned long __start___kcrctab_gpl_future[];
+extern const unsigned long __start___kcrctab_unused[];
+extern const unsigned long __start___kcrctab_unused_gpl[];
 
 #ifndef CONFIG_MODVERSIONS
 #define symversion(base, idx) NULL
@@ -144,6 +152,17 @@ static const struct kernel_symbol *lookup_symbol(const char *name,
         return NULL;
 }
 
+static void printk_unused_warning(const char *name)
+{
+        printk(KERN_WARNING "Symbol %s is marked as UNUSED, "
+                "however this module is using it.\n", name);
+        printk(KERN_WARNING "This symbol will go away in the future.\n");
+        printk(KERN_WARNING "Please evalute if this is the right api to use, "
+                "and if it really is, submit a report the linux kernel "
+                "mailinglist together with submitting your code for "
+                "inclusion.\n");
+}
+
 /* Find a symbol, return value, crc and module which owns it */
 static unsigned long __find_symbol(const char *name,
                                    struct module **owner,
@@ -186,6 +205,25 @@ static unsigned long __find_symbol(const char *name,
                 return ks->value;
         }
 
+        ks = lookup_symbol(name, __start___ksymtab_unused,
+                                 __stop___ksymtab_unused);
+        if (ks) {
+                printk_unused_warning(name);
+                *crc = symversion(__start___kcrctab_unused,
+                                  (ks - __start___ksymtab_unused));
+                return ks->value;
+        }
+
+        if (gplok)
+                ks = lookup_symbol(name, __start___ksymtab_unused_gpl,
+                                 __stop___ksymtab_unused_gpl);
+        if (ks) {
+                printk_unused_warning(name);
+                *crc = symversion(__start___kcrctab_unused_gpl,
+                                  (ks - __start___ksymtab_unused_gpl));
+                return ks->value;
+        }
+
         /* Now try modules. */ 
         list_for_each_entry(mod, &modules, list) {
                 *owner = mod;
@@ -204,6 +242,23 @@ static unsigned long __find_symbol(const char *name,
                                 return ks->value;
                         }
                 }
+                ks = lookup_symbol(name, mod->unused_syms, mod->unused_syms + mod->num_unused_syms);
+                if (ks) {
+                        printk_unused_warning(name);
+                        *crc = symversion(mod->unused_crcs, (ks - mod->unused_syms));
+                        return ks->value;
+                }
+
+                if (gplok) {
+                        ks = lookup_symbol(name, mod->unused_gpl_syms,
+                                           mod->unused_gpl_syms + mod->num_unused_gpl_syms);
+                        if (ks) {
+                                printk_unused_warning(name);
+                                *crc = symversion(mod->unused_gpl_crcs,
+                                                  (ks - mod->unused_gpl_syms));
+                                return ks->value;
+                        }
+                }
                 ks = lookup_symbol(name, mod->gpl_future_syms,
                                    (mod->gpl_future_syms +
                                     mod->num_gpl_future_syms));
@@ -1407,6 +1462,8 @@ static struct module *load_module(void __user *umod,
                 exportindex, modindex, obsparmindex, infoindex, gplindex,
                 crcindex, gplcrcindex, versindex, pcpuindex, gplfutureindex,
                 gplfuturecrcindex, unwindex = 0;
+        unsigned int unusedindex, unusedcrcindex, unusedgplindex,
+                        unusedgplcrcindex;
         struct module *mod;
         long err = 0;
         void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -1487,9 +1544,13 @@ static struct module *load_module(void __user *umod,
         exportindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab");
         gplindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_gpl");
         gplfutureindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_gpl_future");
+        unusedindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_unused");
+        unusedgplindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_unused_gpl");
         crcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab");
         gplcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_gpl");
         gplfuturecrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_gpl_future");
+        unusedcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_unused");
+        unusedgplcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_unused_gpl");
         setupindex = find_sec(hdr, sechdrs, secstrings, "__param");
         exindex = find_sec(hdr, sechdrs, secstrings, "__ex_table");
         obsparmindex = find_sec(hdr, sechdrs, secstrings, "__obsparm");
@@ -1638,14 +1699,27 @@ static struct module *load_module(void __user *umod,
                 mod->gpl_crcs = (void *)sechdrs[gplcrcindex].sh_addr;
         mod->num_gpl_future_syms = sechdrs[gplfutureindex].sh_size /
                                         sizeof(*mod->gpl_future_syms);
+        mod->num_unused_syms = sechdrs[unusedindex].sh_size /
+                                        sizeof(*mod->unused_syms);
+        mod->num_unused_gpl_syms = sechdrs[unusedgplindex].sh_size /
+                                        sizeof(*mod->unused_gpl_syms);
         mod->gpl_future_syms = (void *)sechdrs[gplfutureindex].sh_addr;
         if (gplfuturecrcindex)
                 mod->gpl_future_crcs = (void *)sechdrs[gplfuturecrcindex].sh_addr;
 
+        mod->unused_syms = (void *)sechdrs[unusedindex].sh_addr;
+        if (unusedcrcindex)
+                mod->unused_crcs = (void *)sechdrs[unusedcrcindex].sh_addr;
+        mod->unused_gpl_syms = (void *)sechdrs[unusedgplindex].sh_addr;
+        if (unusedgplcrcindex)
+                mod->unused_crcs = (void *)sechdrs[unusedgplcrcindex].sh_addr;
+
 #ifdef CONFIG_MODVERSIONS
         if ((mod->num_syms && !crcindex) || 
             (mod->num_gpl_syms && !gplcrcindex) ||
-            (mod->num_gpl_future_syms && !gplfuturecrcindex)) {
+            (mod->num_gpl_future_syms && !gplfuturecrcindex) ||
+            (mod->num_unused_syms && !unusedcrcindex) ||
+            (mod->num_unused_gpl_syms && !unusedgplcrcindex)) {
                 printk(KERN_WARNING "%s: No versions for exported symbols."
                        " Tainting kernel.\n", mod->name);
                 add_taint(TAINT_FORCED_MODULE);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5330911ebd30..e4fcbd12cf6e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -23,6 +23,22 @@ config MAGIC_SYSRQ
           keys are documented in <file:Documentation/sysrq.txt>. Don't say Y
           unless you really know what this hack does.
 
+config UNUSED_SYMBOLS
+        bool "Enable unused/obsolete exported symbols"
+        default y if X86
+        help
+          Unused but exported symbols make the kernel needlessly bigger.  For
+          that reason most of these unused exports will soon be removed.  This
+          option is provided temporarily to provide a transition period in case
+          some external kernel module needs one of these symbols anyway. If you
+          encounter such a case in your module, consider if you are actually
+          using the right API.  (rationale: since nobody in the kernel is using
+          this in a module, there is a pretty good chance it's actually the
+          wrong interface to use).  If you really need the symbol, please send a
+          mail to the linux kernel mailing list mentioning the symbol and why
+          you really need it, and what the merge plan to the mainline kernel for
+          your module is.
+
 config DEBUG_KERNEL
         bool "Kernel debugging"
         help