module: reduce symbol table for loaded modules (v2)

Discard all symbols not interesting for kallsyms use: absolute,
section, and in the common case (!KALLSYMS_ALL) data ones.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/module.h b/include/linux/module.h
index 1c755b2..1d3ccb1 100644 (file)
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -308,9 +308,13 @@ struct module
 #endif
 
 #ifdef CONFIG_KALLSYMS
-       /* We keep the symbol and string tables for kallsyms. */
-       Elf_Sym *symtab;
-       unsigned int num_symtab;
+       /*
+        * We keep the symbol and string tables for kallsyms.
+        * The core_* fields below are temporary, loader-only (they
+        * could really be discarded after module init).
+        */
+       Elf_Sym *symtab, *core_symtab;
+       unsigned int num_symtab, core_num_syms;
        char *strtab;
 
        /* Section attributes */

diff --git a/kernel/module.c b/kernel/module.c
index e6bc4b2..97f4d5e 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1862,13 +1862,68 @@ static char elf_type(const Elf_Sym *sym,
        return '?';
 }
 
+static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
+                           unsigned int shnum)
+{
+       const Elf_Shdr *sec;
+
+       if (src->st_shndx == SHN_UNDEF
+           || src->st_shndx >= shnum
+           || !src->st_name)
+               return false;
+
+       sec = sechdrs + src->st_shndx;
+       if (!(sec->sh_flags & SHF_ALLOC)
+#ifndef CONFIG_KALLSYMS_ALL
+           || !(sec->sh_flags & SHF_EXECINSTR)
+#endif
+           || (sec->sh_entsize & INIT_OFFSET_MASK))
+               return false;
+
+       return true;
+}
+
+static unsigned long layout_symtab(struct module *mod,
+                                  Elf_Shdr *sechdrs,
+                                  unsigned int symindex,
+                                  const Elf_Ehdr *hdr,
+                                  const char *secstrings)
+{
+       unsigned long symoffs;
+       Elf_Shdr *symsect = sechdrs + symindex;
+       const Elf_Sym *src;
+       unsigned int i, nsrc, ndst;
+
+       /* Put symbol section at end of init part of module. */
+       symsect->sh_flags |= SHF_ALLOC;
+       symsect->sh_entsize = get_offset(mod, &mod->init_size, symsect,
+                                        symindex) | INIT_OFFSET_MASK;
+       DEBUGP("\t%s\n", secstrings + symsect->sh_name);
+
+       src = (void *)hdr + symsect->sh_offset;
+       nsrc = symsect->sh_size / sizeof(*src);
+       for (ndst = i = 1; i < nsrc; ++i, ++src)
+               if (is_core_symbol(src, sechdrs, hdr->e_shnum))
+                       ++ndst;
+
+       /* Append room for core symbols at end of core part. */
+       symoffs = ALIGN(mod->core_size, symsect->sh_addralign ?: 1);
+       mod->core_size = symoffs + ndst * sizeof(Elf_Sym);
+
+       return symoffs;
+}
+
 static void add_kallsyms(struct module *mod,
                         Elf_Shdr *sechdrs,
+                        unsigned int shnum,
                         unsigned int symindex,
                         unsigned int strindex,
+                        unsigned long symoffs,
                         const char *secstrings)
 {
-       unsigned int i;
+       unsigned int i, ndst;
+       const Elf_Sym *src;
+       Elf_Sym *dst;
 
        mod->symtab = (void *)sechdrs[symindex].sh_addr;
        mod->num_symtab = sechdrs[symindex].sh_size / sizeof(Elf_Sym);
@@ -1878,12 +1933,32 @@ static void add_kallsyms(struct module *mod,
        for (i = 0; i < mod->num_symtab; i++)
                mod->symtab[i].st_info
                        = elf_type(&mod->symtab[i], sechdrs, secstrings, mod);
+
+       mod->core_symtab = dst = mod->module_core + symoffs;
+       src = mod->symtab;
+       *dst = *src;
+       for (ndst = i = 1; i < mod->num_symtab; ++i, ++src) {
+               if (!is_core_symbol(src, sechdrs, shnum))
+                       continue;
+               dst[ndst] = *src;
+               ++ndst;
+       }
+       mod->core_num_syms = ndst;
 }
 #else
+static inline unsigned long layout_symtab(struct module *mod,
+                                         Elf_Shdr *sechdrs,
+                                         unsigned int symindex,
+                                         const Elf_Hdr *hdr,
+                                         const char *secstrings)
+{
+}
 static inline void add_kallsyms(struct module *mod,
                                Elf_Shdr *sechdrs,
+                               unsigned int shnum,
                                unsigned int symindex,
                                unsigned int strindex,
+                               unsigned long symoffs,
                                const char *secstrings)
 {
 }
@@ -1959,6 +2034,9 @@ static noinline struct module *load_module(void __user *umod,
        struct module *mod;
        long err = 0;
        void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
+#ifdef CONFIG_KALLSYMS
+       unsigned long symoffs;
+#endif
        mm_segment_t old_fs;
 
        DEBUGP("load_module: umod=%p, len=%lu, uargs=%p\n",
@@ -2041,8 +2119,7 @@ static noinline struct module *load_module(void __user *umod,
        sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
        sechdrs[versindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
 #ifdef CONFIG_KALLSYMS
-       /* Keep symbol and string tables for decoding later. */
-       sechdrs[symindex].sh_flags |= SHF_ALLOC;
+       /* Keep string table for decoding later. */
        sechdrs[strindex].sh_flags |= SHF_ALLOC;
 #endif
 
@@ -2109,6 +2186,7 @@ static noinline struct module *load_module(void __user *umod,
           this is done generically; there doesn't appear to be any
           special cases for the architectures. */
        layout_sections(mod, hdr, sechdrs, secstrings);
+       symoffs = layout_symtab(mod, sechdrs, symindex, hdr, secstrings);
 
        /* Do the allocs. */
        ptr = module_alloc_update_bounds(mod->core_size);
@@ -2313,7 +2391,8 @@ static noinline struct module *load_module(void __user *umod,
        percpu_modcopy(mod->percpu, (void *)sechdrs[pcpuindex].sh_addr,
                       sechdrs[pcpuindex].sh_size);
 
-       add_kallsyms(mod, sechdrs, symindex, strindex, secstrings);
+       add_kallsyms(mod, sechdrs, hdr->e_shnum, symindex, strindex,
+                    symoffs, secstrings);
 
        if (!mod->taints) {
                struct _ddebug *debug;
@@ -2491,6 +2570,10 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
        /* Drop initial reference. */
        module_put(mod);
        trim_init_extable(mod);
+#ifdef CONFIG_KALLSYMS
+       mod->num_symtab = mod->core_num_syms;
+       mod->symtab = mod->core_symtab;
+#endif
        module_free(mod, mod->module_init);
        mod->module_init = NULL;
        mod->init_size = 0;