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 <siddhesh.poyarekar@gmail.com>
Link: http://lkml.kernel.org/r/1330273075-2949-1-git-send-email-siddhesh.poyarekar@gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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