allow bug table entries to use relative pointers (and use it on x86-64)

Impact: reduce bug table size

This allows reducing the bug table size by half. Perhaps there are
other 64-bit architectures that could also make use of this.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

4 files changed, 30 insertions, 3 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ac22bb7719f7..ab98cca84e1b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -87,6 +87,10 @@ config GENERIC_IOMAP
 config GENERIC_BUG
         def_bool y
         depends on BUG
+        select GENERIC_BUG_RELATIVE_POINTERS if X86_64
+
+config GENERIC_BUG_RELATIVE_POINTERS
+        bool
 
 config GENERIC_HWEIGHT
         def_bool y
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 3def2065fcea..d9cf1cd156d2 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -9,7 +9,7 @@
 #ifdef CONFIG_X86_32
 # define __BUG_C0       "2:\t.long 1b, %c0\n"
 #else
-# define __BUG_C0       "2:\t.quad 1b, %c0\n"
+# define __BUG_C0       "2:\t.long 1b - 2b, %c0 - 2b\n"
 #endif
 
 #define BUG()                                                   \
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 12c07c1866b2..4c794d73fb84 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -8,9 +8,17 @@
 #ifdef CONFIG_GENERIC_BUG
 #ifndef __ASSEMBLY__
 struct bug_entry {
+#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
         unsigned long   bug_addr;
+#else
+        signed int      bug_addr_disp;
+#endif
 #ifdef CONFIG_DEBUG_BUGVERBOSE
+#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
         const char      *file;
+#else
+        signed int      file_disp;
+#endif
         unsigned short  line;
 #endif
         unsigned short  flags;
diff --git a/lib/bug.c b/lib/bug.c
index bfeafd60ee9f..300e41afbf97 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -5,6 +5,8 @@
 
   CONFIG_BUG - emit BUG traps.  Nothing happens without this.
   CONFIG_GENERIC_BUG - enable this code.
+  CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
+        the containing struct bug_entry for bug_addr and file.
   CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
 
   CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
@@ -43,6 +45,15 @@
 
 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
 
+static inline unsigned long bug_addr(const struct bug_entry *bug)
+{
+#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
+        return bug->bug_addr;
+#else
+        return (unsigned long)bug + bug->bug_addr_disp;
+#endif
+}
+
 #ifdef CONFIG_MODULES
 static LIST_HEAD(module_bug_list);
 
@@ -55,7 +66,7 @@ static const struct bug_entry *module_find_bug(unsigned long bugaddr)
                 unsigned i;
 
                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
-                        if (bugaddr == bug->bug_addr)
+                        if (bugaddr == bug_addr(bug))
                                 return bug;
         }
         return NULL;
@@ -108,7 +119,7 @@ const struct bug_entry *find_bug(unsigned long bugaddr)
         const struct bug_entry *bug;
 
         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
-                if (bugaddr == bug->bug_addr)
+                if (bugaddr == bug_addr(bug))
                         return bug;
 
         return module_find_bug(bugaddr);
@@ -133,7 +144,11 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 
         if (bug) {
 #ifdef CONFIG_DEBUG_BUGVERBOSE
+#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
                 file = bug->file;
+#else
+                file = (const char *)bug + bug->file_disp;
+#endif
                 line = bug->line;
 #endif
                 warning = (bug->flags & BUGFLAG_WARNING) != 0;