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Commit e40cd10c authored Mar 05, 2008 by Aurelien Jarno Committed by Ingo Molnar Mar 07, 2008

x86: clear DF before calling signal handler



The Linux kernel currently does not clear the direction flag before
calling a signal handler, whereas the x86/x86-64 ABI requires that.

Linux had this behavior/bug forever, but this becomes a real problem
with gcc version 4.3, which assumes that the direction flag is
correctly cleared at the entry of a function.

This patches changes the setup_frame() functions to clear the
direction before entering the signal handler.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: H. Peter Anvin <hpa@zytor.com>

parent ce4796d1

arch/x86/ia32/ia32_signal.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -500,7 +500,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka,
	regs->ss = __USER32_DS;		regs->ss = __USER32_DS;

	set_fs(USER_DS);		set_fs(USER_DS);
	regs->flags &= ~X86_EFLAGS_TF;		regs->flags &= ~(X86_EFLAGS_TF \| X86_EFLAGS_DF);
	if (test_thread_flag(TIF_SINGLESTEP))		if (test_thread_flag(TIF_SINGLESTEP))
	ptrace_notify(SIGTRAP);		ptrace_notify(SIGTRAP);

	@@ -600,7 +600,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction ka, siginfo_t info,
	regs->ss = __USER32_DS;		regs->ss = __USER32_DS;

	set_fs(USER_DS);		set_fs(USER_DS);
	regs->flags &= ~X86_EFLAGS_TF;		regs->flags &= ~(X86_EFLAGS_TF \| X86_EFLAGS_DF);
	if (test_thread_flag(TIF_SINGLESTEP))		if (test_thread_flag(TIF_SINGLESTEP))
	ptrace_notify(SIGTRAP);		ptrace_notify(SIGTRAP);

arch/x86/kernel/signal_32.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -407,7 +407,7 @@ static int setup_frame(int sig, struct k_sigaction *ka,
	* The tracer may want to single-step inside the		* The tracer may want to single-step inside the
	* handler too.		* handler too.
	*/		*/
	regs->flags &= ~TF_MASK;		regs->flags &= ~(TF_MASK \| X86_EFLAGS_DF);
	if (test_thread_flag(TIF_SINGLESTEP))		if (test_thread_flag(TIF_SINGLESTEP))
	ptrace_notify(SIGTRAP);		ptrace_notify(SIGTRAP);

	@@ -500,7 +500,7 @@ static int setup_rt_frame(int sig, struct k_sigaction ka, siginfo_t info,
	* The tracer may want to single-step inside the		* The tracer may want to single-step inside the
	* handler too.		* handler too.
	*/		*/
	regs->flags &= ~TF_MASK;		regs->flags &= ~(TF_MASK \| X86_EFLAGS_DF);
	if (test_thread_flag(TIF_SINGLESTEP))		if (test_thread_flag(TIF_SINGLESTEP))
	ptrace_notify(SIGTRAP);		ptrace_notify(SIGTRAP);

arch/x86/kernel/signal_64.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -295,7 +295,7 @@ static int setup_rt_frame(int sig, struct k_sigaction ka, siginfo_t info,
	see include/asm-x86_64/uaccess.h for details. */		see include/asm-x86_64/uaccess.h for details. */
	set_fs(USER_DS);		set_fs(USER_DS);

	regs->flags &= ~X86_EFLAGS_TF;		regs->flags &= ~(X86_EFLAGS_TF \| X86_EFLAGS_DF);
	if (test_thread_flag(TIF_SINGLESTEP))		if (test_thread_flag(TIF_SINGLESTEP))
	ptrace_notify(SIGTRAP);		ptrace_notify(SIGTRAP);
	#ifdef DEBUG_SIG		#ifdef DEBUG_SIG