[PATCH] x86_64: reliable stack trace support

These are the generic bits needed to enable reliable stack traces based
on Dwarf2-like (.eh_frame) unwind information. Subsequent patches will
enable x86-64 and i386 to make use of this.

Thanks to Andi Kleen and Ingo Molnar, who pointed out several possibilities
for improvement.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/kernel/module.c b/kernel/module.c
index d75275de1c28..08811e26ac9d 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -40,6 +40,7 @@
 #include <linux/string.h>
 #include <linux/sched.h>
 #include <linux/mutex.h>
+#include <linux/unwind.h>
 #include <asm/uaccess.h>
 #include <asm/semaphore.h>
 #include <asm/cacheflush.h>
@@ -1051,6 +1052,8 @@ static void free_module(struct module *mod)
         remove_sect_attrs(mod);
         mod_kobject_remove(mod);
 
+        unwind_remove_table(mod->unwind_info, 0);
+
         /* Arch-specific cleanup. */
         module_arch_cleanup(mod);
 
@@ -1412,7 +1415,7 @@ static struct module *load_module(void __user *umod,
         unsigned int i, symindex = 0, strindex = 0, setupindex, exindex,
                 exportindex, modindex, obsparmindex, infoindex, gplindex,
                 crcindex, gplcrcindex, versindex, pcpuindex, gplfutureindex,
-                gplfuturecrcindex;
+                gplfuturecrcindex, unwindex = 0;
         struct module *mod;
         long err = 0;
         void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -1502,6 +1505,9 @@ static struct module *load_module(void __user *umod,
         versindex = find_sec(hdr, sechdrs, secstrings, "__versions");
         infoindex = find_sec(hdr, sechdrs, secstrings, ".modinfo");
         pcpuindex = find_pcpusec(hdr, sechdrs, secstrings);
+#ifdef ARCH_UNWIND_SECTION_NAME
+        unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
+#endif
 
         /* Don't keep modinfo section */
         sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
@@ -1510,6 +1516,8 @@ static struct module *load_module(void __user *umod,
         sechdrs[symindex].sh_flags |= SHF_ALLOC;
         sechdrs[strindex].sh_flags |= SHF_ALLOC;
 #endif
+        if (unwindex)
+                sechdrs[unwindex].sh_flags |= SHF_ALLOC;
 
         /* Check module struct version now, before we try to use module. */
         if (!check_modstruct_version(sechdrs, versindex, mod)) {
@@ -1738,6 +1746,11 @@ static struct module *load_module(void __user *umod,
                 goto arch_cleanup;
         add_sect_attrs(mod, hdr->e_shnum, secstrings, sechdrs);
 
+        /* Size of section 0 is 0, so this works well if no unwind info. */
+        mod->unwind_info = unwind_add_table(mod,
+                                            (void *)sechdrs[unwindex].sh_addr,
+                                            sechdrs[unwindex].sh_size);
+
         /* Get rid of temporary copy */
         vfree(hdr);
 
@@ -1836,6 +1849,7 @@ sys_init_module(void __user *umod,
         mod->state = MODULE_STATE_LIVE;
         /* Drop initial reference. */
         module_put(mod);
+        unwind_remove_table(mod->unwind_info, 1);
         module_free(mod, mod->module_init);
         mod->module_init = NULL;
         mod->init_size = 0;