linux-2.6.33/RELOC_HIDE()(gcc)

参照元†

linux-2.6.33/RELOC_HIDE()

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説明†

パス: linux-2.6.33/include/linux/compiler-gcc.h

FIXME: これは何？
- 説明

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実装†

/*
 * This macro obfuscates arithmetic on a variable address so that gcc
 * shouldn't recognize the original var, and make assumptions about it.
 *
 * This is needed because the C standard makes it undefined to do
 * pointer arithmetic on "objects" outside their boundaries and the
 * gcc optimizers assume this is the case. In particular they
 * assume such arithmetic does not wrap.
 *
 * A miscompilation has been observed because of this on PPC.
 * To work around it we hide the relationship of the pointer and the object
 * using this macro.
 *
 * Versions of the ppc64 compiler before 4.1 had a bug where use of
 * RELOC_HIDE could trash r30. The bug can be worked around by changing
 * the inline assembly constraint from =g to =r, in this particular
 * case either is valid.
 */
#define RELOC_HIDE(ptr, off)                                    \
  ({ unsigned long __ptr;                                       \
    __asm__ ("" : "=r"(__ptr) : "0"(ptr));              \
    (typeof(ptr)) (__ptr + (off)); })

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