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    Subject[PATCH] 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.
    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

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