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    Subject[tip:x86/process] x86_64: Record stack pointer before task execution begins
    Commit-ID:  42dfc43ee5999ac64284476ea0ac6c937587cf2b
    Author: Siddhesh Poyarekar <>
    AuthorDate: Sun, 26 Feb 2012 21:47:55 +0530
    Committer: H. Peter Anvin <>
    CommitDate: Sun, 26 Feb 2012 12:59:04 -0800

    x86_64: Record stack pointer before task execution begins

    task->thread.usersp is unusable immediately after a binary is exec()'d
    until it undergoes a context switch cycle. The start_thread() function
    called during execve() saves the stack pointer into pt_regs and into
    old_rsp, but fails to record it into task->thread.usersp.

    Because of this, KSTK_ESP(task) returns an incorrect value for a
    64-bit program until the task is switched out and back in since
    switch_to swaps %rsp values in and out into task->thread.usersp.

    Signed-off-by: Siddhesh Poyarekar <>
    Signed-off-by: H. Peter Anvin <>
    arch/x86/kernel/process_64.c | 1 +
    1 files changed, 1 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    index 1fd94bc..eb54dd0 100644
    --- a/arch/x86/kernel/process_64.c
    +++ b/arch/x86/kernel/process_64.c
    @@ -341,6 +341,7 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip,
    loadsegment(es, _ds);
    loadsegment(ds, _ds);
    + current->thread.usersp = new_sp;
    regs->ip = new_ip;
    regs->sp = new_sp;
    percpu_write(old_rsp, new_sp);

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