arch/x86/include/uapi/asm/ucontext.h

   1 #ifndef _ASM_X86_UCONTEXT_H
   2 #define _ASM_X86_UCONTEXT_H
   3
   4 /*
   5  * Indicates the presence of extended state information in the memory
   6  * layout pointed by the fpstate pointer in the ucontext's sigcontext
   7  * struct (uc_mcontext).
   8  */
   9 #define UC_FP_XSTATE    0x1
  10
  11 #ifdef __x86_64__
  12 /*
  13  * UC_SIGCONTEXT_SS will be set when delivering 64-bit or x32 signals on
  14  * kernels that save SS in the sigcontext.  All kernels that set
  15  * UC_SIGCONTEXT_SS will correctly restore at least the low 32 bits of esp
  16  * regardless of SS (i.e. they implement espfix).
  17  *
  18  * Kernels that set UC_SIGCONTEXT_SS will also set UC_STRICT_RESTORE_SS
  19  * when delivering a signal that came from 64-bit code.
  20  *
  21  * Sigreturn restores SS as follows:
  22  *
  23  * if (saved SS is valid || UC_STRICT_RESTORE_SS is set ||
  24  *     saved CS is not 64-bit)
  25  *         new SS = saved SS  (will fail IRET and signal if invalid)
  26  * else
  27  *         new SS = a flat 32-bit data segment
  28  *
  29  * This behavior serves three purposes:
  30  *
  31  * - Legacy programs that construct a 64-bit sigcontext from scratch
  32  *   with zero or garbage in the SS slot (e.g. old CRIU) and call
  33  *   sigreturn will still work.
  34  *
  35  * - Old DOSEMU versions sometimes catch a signal from a segmented
  36  *   context, delete the old SS segment (with modify_ldt), and change
  37  *   the saved CS to a 64-bit segment.  These DOSEMU versions expect
  38  *   sigreturn to send them back to 64-bit mode without killing them,
  39  *   despite the fact that the SS selector when the signal was raised is
  40  *   no longer valid.  UC_STRICT_RESTORE_SS will be clear, so the kernel
  41  *   will fix up SS for these DOSEMU versions.
  42  *
  43  * - Old and new programs that catch a signal and return without
  44  *   modifying the saved context will end up in exactly the state they
  45  *   started in, even if they were running in a segmented context when
  46  *   the signal was raised..  Old kernels would lose track of the
  47  *   previous SS value.
  48  */
  49 #define UC_SIGCONTEXT_SS        0x2
  50 #define UC_STRICT_RESTORE_SS    0x4
  51 #endif
  52
  53 #include <asm-generic/ucontext.h>
  54
  55 #endif /* _ASM_X86_UCONTEXT_H */