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authorPeter Zijlstra <peterz@infradead.org>2017-02-02 14:43:51 +0100
committerIngo Molnar <mingo@kernel.org>2017-03-27 10:20:28 +0200
commit9a93848fe787a53aec404e4e00d8f7f9bbdaebb4 (patch)
tree4e3b4f0b97838278a72f47a4b4ed2825610e1969 /arch/x86/include/asm/bug.h
parent1fa9d67a2f07893fc7e4a880867a6cbb81dda547 (diff)
x86/debug: Implement __WARN() using UD0
By using "UD0" for WARN()s we remove the function call and its possible __FILE__ and __LINE__ immediate arguments from the instruction stream. Total image size will not change much, what we win in the instruction stream we'll lose because of the __bug_table entries. Still, saves on I$ footprint and the total image size does go down a bit. text data filename 10702123 4530992 defconfig-build/vmlinux.orig 10682460 4530992 defconfig-build/vmlinux.patched (UML didn't seem to use GENERIC_BUG at all, so remove it) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Richard Weinberger <richard.weinberger@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/include/asm/bug.h')
-rw-r--r--arch/x86/include/asm/bug.h78
1 files changed, 60 insertions, 18 deletions
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index ba38ebbaced3..4fde330c44b7 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -1,36 +1,78 @@
#ifndef _ASM_X86_BUG_H
#define _ASM_X86_BUG_H
-#define HAVE_ARCH_BUG
+#include <linux/stringify.h>
-#ifdef CONFIG_DEBUG_BUGVERBOSE
+/*
+ * Since some emulators terminate on UD2, we cannot use it for WARN.
+ * Since various instruction decoders disagree on the length of UD1,
+ * we cannot use it either. So use UD0 for WARN.
+ *
+ * (binutils knows about "ud1" but {en,de}codes it as 2 bytes, whereas
+ * our kernel decoder thinks it takes a ModRM byte, which seems consistent
+ * with various things like the Intel SDM instruction encoding rules)
+ */
+
+#define ASM_UD0 ".byte 0x0f, 0xff"
+#define ASM_UD1 ".byte 0x0f, 0xb9" /* + ModRM */
+#define ASM_UD2 ".byte 0x0f, 0x0b"
+
+#define INSN_UD0 0xff0f
+#define INSN_UD2 0x0b0f
+
+#define LEN_UD0 2
+
+#ifdef CONFIG_GENERIC_BUG
+#define HAVE_ARCH_BUG
#ifdef CONFIG_X86_32
-# define __BUG_C0 "2:\t.long 1b, %c0\n"
+# define __BUG_REL(val) ".long " __stringify(val)
#else
-# define __BUG_C0 "2:\t.long 1b - 2b, %c0 - 2b\n"
+# define __BUG_REL(val) ".long " __stringify(val) " - 2b"
#endif
-#define BUG() \
-do { \
- asm volatile("1:\tud2\n" \
- ".pushsection __bug_table,\"a\"\n" \
- __BUG_C0 \
- "\t.word %c1, 0\n" \
- "\t.org 2b+%c2\n" \
- ".popsection" \
- : : "i" (__FILE__), "i" (__LINE__), \
- "i" (sizeof(struct bug_entry))); \
- unreachable(); \
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+#define _BUG_FLAGS(ins, flags) \
+do { \
+ asm volatile("1:\t" ins "\n" \
+ ".pushsection __bug_table,\"a\"\n" \
+ "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
+ "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \
+ "\t.word %c1" "\t# bug_entry::line\n" \
+ "\t.word %c2" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c3\n" \
+ ".popsection" \
+ : : "i" (__FILE__), "i" (__LINE__), \
+ "i" (flags), \
+ "i" (sizeof(struct bug_entry))); \
} while (0)
-#else
+#else /* !CONFIG_DEBUG_BUGVERBOSE */
+
+#define _BUG_FLAGS(ins, flags) \
+do { \
+ asm volatile("1:\t" ins "\n" \
+ ".pushsection __bug_table,\"a\"\n" \
+ "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
+ "\t.word %c0" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c1\n" \
+ ".popsection" \
+ : : "i" (flags), \
+ "i" (sizeof(struct bug_entry))); \
+} while (0)
+
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+
#define BUG() \
do { \
- asm volatile("ud2"); \
+ _BUG_FLAGS(ASM_UD2, 0); \
unreachable(); \
} while (0)
-#endif
+
+#define __WARN_TAINT(taint) _BUG_FLAGS(ASM_UD0, BUGFLAG_TAINT(taint))
+
+#endif /* CONFIG_GENERIC_BUG */
#include <asm-generic/bug.h>