kernel: constructor support

Call constructors (gcc-generated initcall-like functions) during kernel start and module load. Constructors are e.g. used for gcov data initialization. Disable constructor support for usermode Linux to prevent conflicts with host glibc. Signed-off-by: Peter Oberparleiter <[email protected]> Acked-by: Rusty Russell <[email protected]> Acked-by: WANG Cong <[email protected]> Cc: Sam Ravnborg <[email protected]> Cc: Jeff Dike <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Huang Ying <[email protected]> Cc: Li Wei <[email protected]> Cc: Michael Ellerman <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Heiko Carstens <[email protected]> Cc: Martin Schwidefsky <[email protected]> Cc: Al Viro <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
primiano · Jun 18, 2009 · b99b87f · b99b87f
1 parent e24aca6
commit b99b87f
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diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
@@ -14,6 +14,9 @@ extern char __kprobes_text_start[], __kprobes_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
 
+/* Start and end of .ctors section - used for constructor calls. */
+extern char __ctors_start[], __ctors_end[];
+
 /* function descriptor handling (if any). Override
  * in asm/sections.h */
 #ifndef dereference_function_descriptor

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
@@ -440,12 +440,21 @@
  INIT_TASK \
  }
 
+#ifdef CONFIG_CONSTRUCTORS
+#define KERNEL_CTORS() VMLINUX_SYMBOL(__ctors_start) = .; \
+ *(.ctors) \
+ VMLINUX_SYMBOL(__ctors_end) = .;
+#else
+#define KERNEL_CTORS()
+#endif
+
 /* init and exit section handling */
 #define INIT_DATA \
  *(.init.data) \
  DEV_DISCARD(init.data) \
  CPU_DISCARD(init.data) \
  MEM_DISCARD(init.data) \
+ KERNEL_CTORS() \
  *(.init.rodata) \
  DEV_DISCARD(init.rodata) \
  CPU_DISCARD(init.rodata) \

diff --git a/include/linux/init.h b/include/linux/init.h
@@ -134,6 +134,9 @@ typedef void (*exitcall_t)(void);
 extern initcall_t __con_initcall_start[], __con_initcall_end[];
 extern initcall_t __security_initcall_start[], __security_initcall_end[];
 
+/* Used for contructor calls. */
+typedef void (*ctor_fn_t)(void);
+
 /* Defined in init/main.c */
 extern int do_one_initcall(initcall_t fn);
 extern char __initdata boot_command_line[];

diff --git a/include/linux/module.h b/include/linux/module.h
@@ -363,6 +363,12 @@ struct module
  local_t ref;
 #endif
 #endif
+
+#ifdef CONFIG_CONSTRUCTORS
+ /* Constructor functions. */
+ ctor_fn_t *ctors;
+ unsigned int num_ctors;
+#endif
 };
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}

diff --git a/init/Kconfig b/init/Kconfig
@@ -16,6 +16,11 @@ config DEFCONFIG_LIST
  default "$ARCH_DEFCONFIG"
  default "arch/$ARCH/defconfig"
 
+config CONSTRUCTORS
+ bool
+ depends on !UML
+ default y
+
 menu "General setup"
 
 config EXPERIMENTAL

diff --git a/init/main.c b/init/main.c
@@ -720,6 +720,17 @@ asmlinkage void __init start_kernel(void)
  rest_init();
 }
 
+/* Call all constructor functions linked into the kernel. */
+static void __init do_ctors(void)
+{
+#ifdef CONFIG_CONSTRUCTORS
+ ctor_fn_t *call = (ctor_fn_t *) __ctors_start;
+
+ for (; call < (ctor_fn_t *) __ctors_end; call++)
+ (*call)();
+#endif
+}
+
 int initcall_debug;
 core_param(initcall_debug, initcall_debug, bool, 0644);
 
@@ -800,6 +811,7 @@ static void __init do_basic_setup(void)
  usermodehelper_init();
  driver_init();
  init_irq_proc();
+ do_ctors();
  do_initcalls();
 }
 

diff --git a/kernel/module.c b/kernel/module.c
@@ -2216,6 +2216,10 @@ static noinline struct module *load_module(void __user *umod,
  mod->unused_gpl_crcs = section_addr(hdr, sechdrs, secstrings,
  "__kcrctab_unused_gpl");
 #endif
+#ifdef CONFIG_CONSTRUCTORS
+ mod->ctors = section_objs(hdr, sechdrs, secstrings, ".ctors",
+ sizeof(*mod->ctors), &mod->num_ctors);
+#endif
 
 #ifdef CONFIG_MARKERS
  mod->markers = section_objs(hdr, sechdrs, secstrings, "__markers",
@@ -2389,6 +2393,17 @@ static noinline struct module *load_module(void __user *umod,
  goto free_hdr;
 }
 
+/* Call module constructors. */
+static void do_mod_ctors(struct module *mod)
+{
+#ifdef CONFIG_CONSTRUCTORS
+ unsigned long i;
+
+ for (i = 0; i < mod->num_ctors; i++)
+ mod->ctors[i]();
+#endif
+}
+
 /* This is where the real work happens */
 SYSCALL_DEFINE3(init_module, void __user *, umod,
  unsigned long, len, const char __user *, uargs)
@@ -2417,6 +2432,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
  blocking_notifier_call_chain(&module_notify_list,
  MODULE_STATE_COMING, mod);
 
+ do_mod_ctors(mod);
  /* Start the module */
  if (mod->init != NULL)
  ret = do_one_initcall(mod->init);