Commit 9a93848f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarJosh 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: default avatarIngo Molnar <mingo@kernel.org>
parent 1fa9d67a

arch/um/Kconfig.common

+0 −5
Original line number Diff line number Diff line
@@ -50,11 +50,6 @@ config GENERIC_CALIBRATE_DELAY 
	bool

	default y



config GENERIC_BUG

	bool

	default y

	depends on BUG



config HZ

	int

	default 100

arch/x86/include/asm/bug.h

+60 −18
Original line number Diff line number Diff line 
#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()							\

#ifdef CONFIG_DEBUG_BUGVERBOSE



#define _BUG_FLAGS(ins, flags)						\

do {									\

	asm volatile("1:\tud2\n"				\

	asm volatile("1:\t" ins "\n"					\

		     ".pushsection __bug_table,\"a\"\n"			\

		     __BUG_C0					\

		     "\t.word %c1, 0\n"				\

		     "\t.org 2b+%c2\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)));		\

	unreachable();						\

} 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>

arch/x86/kernel/dumpstack.c

+0 −3
Original line number Diff line number Diff line
@@ -289,9 +289,6 @@ void die(const char *str, struct pt_regs *regs, long err) 
	unsigned long flags = oops_begin();

	int sig = SIGSEGV;



	if (!user_mode(regs))

		report_bug(regs->ip, regs);



	if (__die(str, regs, err))

		sig = 0;

	oops_end(flags, regs, sig);

arch/x86/kernel/dumpstack_32.c

+0 −12
Original line number Diff line number Diff line
@@ -162,15 +162,3 @@ void show_regs(struct pt_regs *regs) 
	}

	pr_cont("\n");

}
 


int is_valid_bugaddr(unsigned long ip)

{

	unsigned short ud2;



	if (ip < PAGE_OFFSET)

		return 0;

	if (probe_kernel_address((unsigned short *)ip, ud2))

		return 0;



	return ud2 == 0x0b0f;

}

arch/x86/kernel/dumpstack_64.c

+0 −10
Original line number Diff line number Diff line
@@ -178,13 +178,3 @@ void show_regs(struct pt_regs *regs) 
	}

	pr_cont("\n");

}
 


int is_valid_bugaddr(unsigned long ip)

{

	unsigned short ud2;



	if (__copy_from_user(&ud2, (const void __user *) ip, sizeof(ud2)))

		return 0;



	return ud2 == 0x0b0f;

}

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