rom/exec/setfunction.c

   1 /*
   2     Copyright © 1995-2008, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Patch a library or device function
   6     Lang: english
   7 */
   8 #include <aros/config.h>
   9 #include <exec/execbase.h>
  10 #include <aros/libcall.h>
  11 #include <proto/exec.h>
  12 #include "exec_debug.h"
  13
  14 #ifndef DEBUG_SetFunction
  15 #   define DEBUG_SetFunction 0
  16 #endif
  17 #undef DEBUG
  18 #if DEBUG_SetFunction
  19 #   define DEBUG 1
  20 #endif
  21 #include <aros/debug.h>
  22 #undef kprintf
  23
  24 /*****************************************************************************
  25
  26     NAME */
  27
  28         AROS_LH3(APTR, SetFunction,
  29
  30 /*  SYNOPSIS */
  31         AROS_LHA(struct Library *, library,     A1),
  32         AROS_LHA(LONG,             funcOffset,  A0),
  33         AROS_LHA(APTR,             newFunction, D0),
  34
  35 /*  LOCATION */
  36         struct ExecBase *, SysBase, 70, Exec)
  37
  38 /*  FUNCTION
  39         Replaces a certain jumptable entry with another one. This function only
  40         Forbid()s taskswitching but doesn't Disable() interrupts. You have
  41         to do your own arbitration for functions which are callable from
  42         interrupts.
  43
  44     INPUTS
  45         library     - Pointer to library structure.
  46         funcOffset  - Offset of the jumpvector from the library base address in
  47                       bytes. It's the negative LVO (library vector offset)
  48                       multiplied with LIB_VECTSIZE.
  49         newFunction - New jumptable entry (pointer to the new function).
  50
  51     RESULT
  52         Old jumptable entry (pointer to the old function).
  53
  54     NOTES
  55         While it's more or less safe to patch a library vector with
  56         SetFunction() it's not possible to safely remove the patch later.
  57         So don't use this function if it can be avoided.
  58
  59     EXAMPLE
  60         Patch of the function Open() from dos.library:
  61         You can find the LVO of 5 in clib/dos_protos.h.
  62         SetFunction(DOSBase, -5 * LIB_VECTSIZE, NewOpen);
  63         NewOpen must be prepared with AROS_UFH macros.
  64
  65     BUGS
  66         On native builds, this contains a hack to fix dos.library/ramlib
  67         attempts to setfunction exec functions. Because of this, a funcOffset
  68         of more than 32 kB be truncated. This hack will also fix other programs
  69         only using the lower 16 bits of funcOffset and leaving garbage in the
  70         upper 16 bits. These programs should be fixed.
  71
  72     SEE ALSO
  73         MakeLibrary(), MakeFunctions(), SumLibrary()
  74
  75     INTERNALS
  76
  77 ******************************************************************************/
  78 {
  79     AROS_LIBFUNC_INIT
  80     APTR ret;
  81 #if (AROS_FLAVOUR & AROS_FLAVOUR_NATIVE)
  82     ULONG *vecaddr;
  83 #endif
  84
  85     D(bug("SetFunction(%s, %lx, %lx) = ", (ULONG)library->lib_Node.ln_Name, funcOffset, (ULONG)newFunction));
  86
  87 #if (AROS_FLAVOUR & AROS_FLAVOUR_NATIVE)
  88     /*
  89         Fix dos.library/ramlib attempts to SetFunction() CloseDevice/
  90         CloseLibrary/RemDevice/RemLibrary/OpenDevice/OpenLibrary.
  91
  92         This also effectively limits the max offset to 32k, but this limit was
  93         already in the original, though not really documented.
  94
  95         What happens is this: the prototype for the funcOffset says it is a
  96         long, but the autodoc also says that only a0.w (lower 16 bits) is used.
  97         Dos.library/ramlib only sets the lower 16 bits of a0 to the required
  98         offset, without sign-extending to the upper 16 bits, in fact without
  99         even clearing them. These high 16 bits will therefore contain garbage:
 100
 101         SetFunction(exec.library, 7804fe3e, fc6524) = 30303030 CloseDevice
 102         SetFunction(exec.library, 3030fe62, fc6528) = 30303030 CloseLibrary
 103         SetFunction(exec.library, 3030fe4a, fc651c) = 30303030 RemDevice
 104         SetFunction(exec.library, 3030fe6e, fc6520) = 30303030 RemLibrary
 105         SetFunction(exec.library, 3030fe44, fc6564) = 30303030 OpenDevice
 106         SetFunction(exec.library, 3030fdd8, fc659a) = 30303030 OpenLibrary
 107
 108         In my [ldp] opinion, the autodoc should never have said that only A0.W
 109         is used for the funcOffset, while specifying a "long" in the prototype.
 110         This will stay broken and this fix will stay here until we fix
 111         dos.library/ramlib.
 112     */
 113     if (funcOffset & 0x00008000)
 114     {
 115         funcOffset |= 0xffff0000;
 116     }
 117     else
 118     {
 119         funcOffset &= 0x0000ffff;
 120     }
 121
 122 #else
 123     /* Vector pre-processing for non-native machines: */
 124     funcOffset = (-funcOffset) / LIB_VECTSIZE;
 125
 126 #endif
 127
 128     /*
 129         Arbitrate for the jumptable. This isn't enough for interrupt callable
 130         functions - but it need not be.
 131     */
 132     Forbid();
 133
 134     /* Mark the library as changed. */
 135     library->lib_Flags|=LIBF_CHANGED;
 136
 137 #if (AROS_FLAVOUR & AROS_FLAVOUR_NATIVE)
 138     /* The following section is coded like this (instead of using the macros),
 139        because else gcc will output 64-bit muls instructions, that are not
 140        present on the 68060 (and will crash it). It's faster this way, too. :) */
 141     vecaddr = (APTR)((ULONG)library + funcOffset);
 142
 143     /* Get the old vector pointer */
 144     ret = (APTR)*(ULONG *)(((ULONG)vecaddr)+2);
 145
 146     /* Set new vector and jmp instruction */
 147     *(UWORD *)vecaddr = 0x4ef9;
 148     *(ULONG *)(((ULONG)vecaddr)+2) = (ULONG)newFunction;
 149
 150 #else /* non-native section follows */
 151     /* Get old vector. */
 152     ret = __AROS_GETVECADDR (library, funcOffset);
 153
 154     /* Don't forget to initialise the vector, or else there would be no actual
 155        assembler jump instruction in the vector */
 156     __AROS_INITVEC (library, funcOffset);
 157
 158     /* Write new one. */
 159     __AROS_SETVECADDR (library, funcOffset, newFunction);
 160
 161 #endif /* end if system specific sections */
 162
 163 #if 1
 164     /* And clear the instruction cache. */
 165     /* Simply clear the entire cache... */
 166     CacheClearU();
 167 #else
 168     /* ...or clear the vector address range specifically */
 169     CacheClearE (__AROS_GETJUMPVEC(library,funcOffset),LIB_VECTSIZE,CACRF_ClearI|CACRF_ClearD);
 170 #endif
 171
 172     /* Arbitration is no longer needed */
 173     Permit();
 174
 175     /* Sum the library up again */
 176     SumLibrary(library);
 177
 178     D(bug("%lx\n", ret));
 179
 180     /* All done. */
 181     return ret;
 182     AROS_LIBFUNC_EXIT
 183 } /* SetFunction */
 184