linux-kernel - [PATCH 4/7] DWARF: initialize structures for kernel and modules

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Date:   Fri,  5 May 2017 14:21:57 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     akpm@...ux-foundation.org
Cc:     torvalds@...ux-foundation.org, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
        Jessica Yu <jeyu@...hat.com>,
        Rusty Russell <rusty@...tcorp.com.au>
Subject: [PATCH 4/7] DWARF: initialize structures for kernel and modules

When booting, initialize eh_frame for use in the DWARF unwinder. Do the
same for every coming module's info.

And destroy the information when a module is going away.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Cc: Jessica Yu <jeyu@...hat.com>
Cc: Rusty Russell <rusty@...tcorp.com.au>
---
 include/linux/module.h |  4 ++++
 init/main.c            |  3 +++
 kernel/module.c        | 32 +++++++++++++++++++++++++++++++-
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 21f56393602f..21f7a23f8004 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -257,6 +257,7 @@ extern const typeof(name) __mod_##type##__##name##_device_table		\
  * files require multiple MODULE_FIRMWARE() specifiers */
 #define MODULE_FIRMWARE(_firmware) MODULE_INFO(firmware, _firmware)
 
+struct dwarf_table;
 struct notifier_block;
 
 #ifdef CONFIG_MODULES
@@ -393,6 +394,9 @@ struct module {
 	struct module_layout core_layout __module_layout_align;
 	struct module_layout init_layout;
 
+	/* The handle returned from dwarf_add_table. */
+	struct dwarf_table *dwarf_info;
+
 	/* Arch-specific module values */
 	struct mod_arch_specific arch;
 
diff --git a/init/main.c b/init/main.c
index cc48053bb39f..5acedeae355d 100644
--- a/init/main.c
+++ b/init/main.c
@@ -22,6 +22,7 @@
 #include <linux/string.h>
 #include <linux/ctype.h>
 #include <linux/delay.h>
+#include <linux/dwarf.h>
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/initrd.h>
@@ -490,6 +491,7 @@ asmlinkage __visible void __init start_kernel(void)
 	char *command_line;
 	char *after_dashes;
 
+	dwarf_init();
 	set_task_stack_end_magic(&init_task);
 	smp_setup_processor_id();
 	debug_objects_early_init();
@@ -514,6 +516,7 @@ asmlinkage __visible void __init start_kernel(void)
 	setup_arch(&command_line);
 	mm_init_cpumask(&init_mm);
 	setup_command_line(command_line);
+	dwarf_setup();
 	setup_nr_cpu_ids();
 	setup_per_cpu_areas();
 	boot_cpu_state_init();
diff --git a/kernel/module.c b/kernel/module.c
index 4a3665f8f837..3571328e41fe 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -38,6 +38,7 @@
 #include <linux/capability.h>
 #include <linux/cpu.h>
 #include <linux/moduleparam.h>
+#include <linux/dwarf.h>
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/vermagic.h>
@@ -314,7 +315,7 @@ struct load_info {
 	unsigned long mod_kallsyms_init_off;
 #endif
 	struct {
-		unsigned int sym, str, mod, vers, info, pcpu;
+		unsigned int sym, str, mod, vers, info, pcpu, dwarf;
 	} index;
 };
 
@@ -753,6 +754,27 @@ bool __is_module_percpu_address(unsigned long addr, unsigned long *can_addr)
 
 #endif /* CONFIG_SMP */
 
+static unsigned int find_dwarf(struct load_info *info)
+{
+	unsigned int section = 0;
+#ifdef ARCH_DWARF_SECTION_NAME
+	section = find_sec(info, ARCH_DWARF_SECTION_NAME);
+	if (section)
+		info->sechdrs[section].sh_flags |= SHF_ALLOC;
+#endif
+	return section;
+}
+
+static void add_dwarf_table(struct module *mod, struct load_info *info)
+{
+	int index = info->index.dwarf;
+
+	/* Size of section 0 is 0, so this is ok if there is no dwarf info. */
+	mod->dwarf_info = dwarf_add_table(mod,
+					  (void *)info->sechdrs[index].sh_addr,
+					  info->sechdrs[index].sh_size);
+}
+
 #define MODINFO_ATTR(field)	\
 static void setup_modinfo_##field(struct module *mod, const char *s)  \
 {                                                                     \
@@ -2133,6 +2155,8 @@ static void free_module(struct module *mod)
 	/* Remove dynamic debug info */
 	ddebug_remove_module(mod->name);
 
+	dwarf_remove_table(mod->dwarf_info, false);
+
 	/* Arch-specific cleanup. */
 	module_arch_cleanup(mod);
 
@@ -2970,6 +2994,8 @@ static struct module *setup_load_info(struct load_info *info, int flags)
 
 	info->index.pcpu = find_pcpusec(info);
 
+	info->index.dwarf = find_dwarf(info);
+
 	/* Check module struct version now, before we try to use module. */
 	if (!check_modstruct_version(info->sechdrs, info->index.vers, mod))
 		return ERR_PTR(-ENOEXEC);
@@ -3459,6 +3485,7 @@ static noinline int do_init_module(struct module *mod)
 	/* Drop initial reference. */
 	module_put(mod);
 	trim_init_extable(mod);
+	dwarf_remove_table(mod->dwarf_info, true);
 #ifdef CONFIG_KALLSYMS
 	/* Switch to core kallsyms now init is done: kallsyms may be walking! */
 	rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
@@ -3734,6 +3761,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
 			goto sysfs_cleanup;
 	}
 
+	/* Initialize dwarf table */
+	add_dwarf_table(mod, info);
+
 	/* Get rid of temporary copy. */
 	free_copy(info);
 
-- 
2.12.2