[PATCH] x86: Clear DF before calling signal handler

Aurelien Jarno
2008-03-05T18:15:27Z

The Linux kernel currently does not clear the direction flag before
calling a signal handler, whereas the x86/x86-64 ABI requires that.
This become 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>
---
arch/x86/ia32/ia32_signal.c | 4 ++--
arch/x86/kernel/signal_32.c | 4 ++--
arch/x86/kernel/signal_64.c | 2 +-
3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 1c0503b..5e7771a 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -500,7 +500,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka,
regs->ss = __USER32_DS;

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

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

diff --git a/arch/x86/kernel/signal_32.c b/arch/x86/kernel/signal_32.c
index caee1f0..0157a6f 100644
--- a/arch/x86/kernel/signal_32.c
+++ b/arch/x86/kernel/signal_32.c
@@ -407,7 +407,7 @@ static int setup_frame(int sig, struct k_sigaction *ka,
* The tracer may want to single-step inside the
* handler too.
*/
- regs->flags &= ~TF_MASK;
+ regs->flags &= ~(TF_MASK | X86_EFLAGS_DF);
if (test_thread_flag(TIF_SINGLESTEP))
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
* handler too.
*/
- regs->flags &= ~TF_MASK;
+ regs->flags &= ~(TF_MASK | X86_EFLAGS_DF);
if (test_thread_flag(TIF_SINGLESTEP))
ptrace_notify(SIGTRAP);

diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index 7347bb1..56b72fb 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -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. */
set_fs(USER_DS);

- regs->flags &= ~X86_EFLAGS_TF;
+ regs->flags &= ~(X86_EFLAGS_TF | X86_EFLAGS_DF);
if (test_thread_flag(TIF_SINGLESTEP))
ptrace_notify(SIGTRAP);
#ifdef DEBUG_SIG
--
1.5.4.3

--
.''`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
`. `' aurel32@debian.org | aurelien@aurel32.net
`- people.debian.org/~aurel32 | www.aurel32.net