1 /* Subroutine for function pointer canonicalization on PA-RISC with ELF32.
2 Copyright 2002 Free Software Foundation, Inc.
3 Contributed by John David Anglin (dave.anglin@nrc.ca).
5 This file is part of GNU CC.
7 GNU CC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2, or (at your option)
12 GNU CC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GNU CC; see the file COPYING. If not, write to
19 the Free Software Foundation, 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
22 /* WARNING: The code is this function depends on internal and undocumented
23 details of the GNU linker and dynamic loader as implemented for parisc
26 /* This MUST match the defines sysdeps/hppa/dl-machine.h and
28 #define GOT_FROM_PLT_STUB (4*4)
30 /* List of byte offsets in _dl_runtime_resolve to search for "bl" branches.
31 The first "bl" branch instruction found MUST be a call to fixup. See
32 the define for TRAMPOLINE_TEMPLATE in sysdeps/hppa/dl-machine.h. If
33 the trampoline template is changed, the list must be appropriately
34 updated. The offset of -4 allows for a magic branch at the start of
35 the template should it be necessary to change the current branch
38 static int fixup_branch_offset[NOFFSETS] = { 32, -4 };
40 #define GET_FIELD(X, FROM, TO) \
41 ((X) >> (31 - (TO)) & ((1 << ((TO) - (FROM) + 1)) - 1))
42 #define SIGN_EXTEND(VAL,BITS) \
43 ((int) ((VAL) >> ((BITS) - 1) ? (-1 << (BITS)) | (VAL) : (VAL)))
46 typedef int (*fptr_t) (void);
47 typedef int (*fixup_t) (struct link_map *, unsigned int);
48 extern unsigned int _GLOBAL_OFFSET_TABLE_;
50 /* __canonicalize_funcptr_for_compare must be hidden so that it is not
51 placed in the dynamic symbol table. Like millicode functions, it
52 must be linked into all binaries in order access the got table of
53 that binary. However, we don't use the millicode calling convention
54 and the routine must be a normal function so that it can be compiled
56 unsigned int __canonicalize_funcptr_for_compare (fptr_t)
57 __attribute__ ((visibility ("hidden")));
60 __canonicalize_funcptr_for_compare (fptr)
63 static unsigned int fixup_plabel[2];
65 unsigned int *plabel, *got;
67 /* -1 and page 0 are special. -1 is used in crtend to mark the end of
68 a list of function pointers. Also return immediately if the plabel
69 bit is not set in the function pointer. In this case, the function
70 pointer points directly to the function. */
71 if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2))
72 return (unsigned int) fptr;
74 /* The function pointer points to a function descriptor (plabel). If
75 the plabel hasn't been resolved, the first word of the plabel points
76 to the entry of the PLT stub just before the global offset table.
77 The second word in the plabel contains the relocation offset for the
79 plabel = (unsigned int *) ((unsigned int) fptr & ~3);
80 got = (unsigned int *) (plabel[0] + GOT_FROM_PLT_STUB);
82 /* Return the address of the function if the plabel has been resolved. */
83 if (got != &_GLOBAL_OFFSET_TABLE_)
86 /* Initialize our plabel for calling fixup if we haven't done so already.
87 This code needs to be thread safe but we don't have to be too careful
88 as the result is invariant. */
94 /* Find the first "bl" branch in the offset search list. This is a
95 call to fixup or a magic branch to fixup at the beginning of the
96 trampoline template. The fixup function does the actual runtime
97 resolution of function descriptors. We only look for "bl" branches
98 with a 17-bit pc-relative displacement. */
99 for (i = 0; i < NOFFSETS; i++)
101 iptr = (unsigned int *) (got[-2] + fixup_branch_offset[i]);
102 if ((*iptr & 0xfc00e000) == 0xe8000000)
106 /* This should not happen... */
110 /* Extract the 17-bit displacement from the instruction. */
111 iptr += SIGN_EXTEND (GET_FIELD (*iptr, 19, 28) |
112 GET_FIELD (*iptr, 29, 29) << 10 |
113 GET_FIELD (*iptr, 11, 15) << 11 |
114 GET_FIELD (*iptr, 31, 31) << 16, 17);
116 /* Build a plabel for an indirect call to fixup. */
117 fixup_plabel[0] = (unsigned int) iptr + 8; /* address of fixup */
118 fixup_plabel[1] = got[-1]; /* ltp for fixup */
119 fixup = (fixup_t) ((int) fixup_plabel | 3);
122 /* Call fixup to resolve the function address. got[1] contains the
123 link_map pointer and plabel[1] the relocation offset. */
124 fixup ((struct link_map *) got[1], plabel[1]);