[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>

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 027285d0c26c1e4e366237e2893b12c231b37a78..033ac91da07a81f0038b05dd52a4ab029d13f509 100644 (file)
--- 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 9d11550b481810e6f459598dcac969187c1f6a4b..db5a3732f1065a79dde1660e8149d70e2a18091b 100644 (file)
--- 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 9ebbb74b7b729ee8fe17a8ed783c1a3327944fb8..9e9dc7c24d9589e50e84913c76f46ac9ec3b2ae5 100644 (file)
--- 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 10e5b872adf6f56d2755976dee65a6e8a9a6ab8a..03b738172a8c31b662ae43b24befd454989aadd5 100644 (file)
--- 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 5330911ebd303ed875657c3e739e5bb966dd5c71..e4fcbd12cf6ef75b75d7eebc40d1b45de3a22236 100644 (file)
--- 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