1 /* Subroutine for function pointer canonicalization on PA-RISC with ELF32.
2 Copyright 2002, 2003, 2004, 2007 Free Software Foundation, Inc.
3 Contributed by John David Anglin (dave.anglin@nrc.ca).
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 3, or (at your option) any later
12 In addition to the permissions in the GNU General Public License, the
13 Free Software Foundation gives you unlimited permission to link the
14 compiled version of this file into combinations with other programs,
15 and to distribute those combinations without any restriction coming
16 from the use of this file. (The General Public License restrictions
17 do apply in other respects; for example, they cover modification of
18 the file, and distribution when not linked into a combine
21 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
22 WARRANTY; without even the implied warranty of MERCHANTABILITY or
23 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
26 You should have received a copy of the GNU General Public License
27 along with GCC; see the file COPYING3. If not see
28 <http://www.gnu.org/licenses/>. */
30 /* WARNING: The code is this function depends on internal and undocumented
31 details of the GNU linker and dynamic loader as implemented for parisc
34 /* This MUST match the defines sysdeps/hppa/dl-machine.h and
36 #define GOT_FROM_PLT_STUB (4*4)
38 /* List of byte offsets in _dl_runtime_resolve to search for "bl" branches.
39 The first "bl" branch instruction found MUST be a call to fixup. See
40 the define for TRAMPOLINE_TEMPLATE in sysdeps/hppa/dl-machine.h. If
41 the trampoline template is changed, the list must be appropriately
42 updated. The offset of -4 allows for a magic branch at the start of
43 the template should it be necessary to change the current branch
46 static int fixup_branch_offset[NOFFSETS] = { 32, -4 };
48 #define GET_FIELD(X, FROM, TO) \
49 ((X) >> (31 - (TO)) & ((1 << ((TO) - (FROM) + 1)) - 1))
50 #define SIGN_EXTEND(VAL,BITS) \
51 ((int) ((VAL) >> ((BITS) - 1) ? (-1 << (BITS)) | (VAL) : (VAL)))
54 typedef int (*fptr_t) (void);
55 typedef int (*fixup_t) (struct link_map *, unsigned int);
56 extern unsigned int _GLOBAL_OFFSET_TABLE_;
58 /* __canonicalize_funcptr_for_compare must be hidden so that it is not
59 placed in the dynamic symbol table. Like millicode functions, it
60 must be linked into all binaries in order access the got table of
61 that binary. However, we don't use the millicode calling convention
62 and the routine must be a normal function so that it can be compiled
64 unsigned int __canonicalize_funcptr_for_compare (fptr_t)
65 __attribute__ ((visibility ("hidden")));
68 __canonicalize_funcptr_for_compare (fptr_t fptr)
70 static unsigned int fixup_plabel[2];
72 unsigned int *plabel, *got;
74 /* -1 and page 0 are special. -1 is used in crtend to mark the end of
75 a list of function pointers. Also return immediately if the plabel
76 bit is not set in the function pointer. In this case, the function
77 pointer points directly to the function. */
78 if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2))
79 return (unsigned int) fptr;
81 /* The function pointer points to a function descriptor (plabel). If
82 the plabel hasn't been resolved, the first word of the plabel points
83 to the entry of the PLT stub just before the global offset table.
84 The second word in the plabel contains the relocation offset for the
86 plabel = (unsigned int *) ((unsigned int) fptr & ~3);
87 got = (unsigned int *) (plabel[0] + GOT_FROM_PLT_STUB);
89 /* Return the address of the function if the plabel has been resolved. */
90 if (got != &_GLOBAL_OFFSET_TABLE_)
93 /* Initialize our plabel for calling fixup if we haven't done so already.
94 This code needs to be thread safe but we don't have to be too careful
95 as the result is invariant. */
101 /* Find the first "bl" branch in the offset search list. This is a
102 call to fixup or a magic branch to fixup at the beginning of the
103 trampoline template. The fixup function does the actual runtime
104 resolution of function descriptors. We only look for "bl" branches
105 with a 17-bit pc-relative displacement. */
106 for (i = 0; i < NOFFSETS; i++)
108 iptr = (unsigned int *) (got[-2] + fixup_branch_offset[i]);
109 if ((*iptr & 0xfc00e000) == 0xe8000000)
113 /* This should not happen... */
117 /* Extract the 17-bit displacement from the instruction. */
118 iptr += SIGN_EXTEND (GET_FIELD (*iptr, 19, 28) |
119 GET_FIELD (*iptr, 29, 29) << 10 |
120 GET_FIELD (*iptr, 11, 15) << 11 |
121 GET_FIELD (*iptr, 31, 31) << 16, 17);
123 /* Build a plabel for an indirect call to fixup. */
124 fixup_plabel[0] = (unsigned int) iptr + 8; /* address of fixup */
125 fixup_plabel[1] = got[-1]; /* ltp for fixup */
126 fixup = (fixup_t) ((int) fixup_plabel | 3);
129 /* Call fixup to resolve the function address. got[1] contains the
130 link_map pointer and plabel[1] the relocation offset. */
131 fixup ((struct link_map *) got[1], plabel[1]);