1 /* Subroutine for function pointer canonicalization on PA-RISC with ELF32.
2 Copyright (C) 2002-2016 Free Software Foundation, Inc.
3 Contributed by John David Anglin (dave.anglin@nrc.ca).
4
5 This file is part of GCC.
6
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
10 version.
11
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 for more details.
16
17 Under Section 7 of GPL version 3, you are granted additional
18 permissions described in the GCC Runtime Library Exception, version
19 3.1, as published by the Free Software Foundation.
20
21 You should have received a copy of the GNU General Public License and
22 a copy of the GCC Runtime Library Exception along with this program;
23 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 <http://www.gnu.org/licenses/>. */
25
26
27 /* WARNING: The code is this function depends on internal and undocumented
28 details of the GNU linker and dynamic loader as implemented for parisc
29 linux. */
30
31 /* This MUST match the defines sysdeps/hppa/dl-machine.h and
32 bfd/elf32-hppa.c. */
33 #define GOT_FROM_PLT_STUB (4*4)
34
35 /* List of byte offsets in _dl_runtime_resolve to search for "bl" branches.
36 The first "bl" branch instruction found MUST be a call to fixup. See
37 the define for TRAMPOLINE_TEMPLATE in sysdeps/hppa/dl-machine.h. If
38 the trampoline template is changed, the list must be appropriately
39 updated. The offset of -4 allows for a magic branch at the start of
40 the template should it be necessary to change the current branch
41 position. */
42 #define NOFFSETS 2
43 static int fixup_branch_offset[NOFFSETS] = { -4, 32 };
44
45 #define GET_FIELD(X, FROM, TO) \
46 ((X) >> (31 - (TO)) & ((1 << ((TO) - (FROM) + 1)) - 1))
47 #define SIGN_EXTEND(VAL,BITS) \
48 ((int) ((VAL) >> ((BITS) - 1) ? ((unsigned)(-1) << (BITS)) | (VAL) : (VAL)))
49
50 struct link_map;
51 typedef int (*fptr_t) (void);
52 typedef int (*fixup_t) (struct link_map *, unsigned int);
53 extern unsigned int _GLOBAL_OFFSET_TABLE_;
54
55 static inline int
_dl_read_access_allowed(unsigned int * addr)56 _dl_read_access_allowed (unsigned int *addr)
57 {
58 int result;
59
60 asm ("proberi (%1),3,%0" : "=r" (result) : "r" (addr) : );
61
62 return result;
63 }
64
65 /* __canonicalize_funcptr_for_compare must be hidden so that it is not
66 placed in the dynamic symbol table. Like millicode functions, it
67 must be linked into all binaries in order access the got table of
68 that binary. However, we don't use the millicode calling convention
69 and the routine must be a normal function so that it can be compiled
70 as pic code. */
71 unsigned int __canonicalize_funcptr_for_compare (fptr_t)
72 __attribute__ ((visibility ("hidden")));
73
74 unsigned int
__canonicalize_funcptr_for_compare(fptr_t fptr)75 __canonicalize_funcptr_for_compare (fptr_t fptr)
76 {
77 static unsigned int fixup_plabel[2] __attribute__((used));
78 fixup_t fixup;
79 unsigned int *got, *iptr, *plabel;
80 int i;
81
82 /* -1 and page 0 are special. -1 is used in crtend to mark the end of
83 a list of function pointers. Also return immediately if the plabel
84 bit is not set in the function pointer. In this case, the function
85 pointer points directly to the function. */
86 if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2))
87 return (unsigned int) fptr;
88
89 /* The function pointer points to a function descriptor (plabel). If
90 the plabel hasn't been resolved, the first word of the plabel points
91 to the entry of the PLT stub just before the global offset table.
92 The second word in the plabel contains the relocation offset for the
93 function. */
94 plabel = (unsigned int *) ((unsigned int) fptr & ~3);
95 if (!_dl_read_access_allowed (plabel))
96 return (unsigned int) fptr;
97
98 /* Load first word of candidate descriptor. It should be a pointer
99 with word alignment and point to memory that can be read. */
100 got = (unsigned int *) plabel[0];
101 if (((unsigned int) got & 3) != 0
102 || !_dl_read_access_allowed (got))
103 return (unsigned int) fptr;
104
105 got = (unsigned int *) (plabel[0] + GOT_FROM_PLT_STUB);
106
107 /* Return the address of the function if the plabel has been resolved. */
108 if (got != &_GLOBAL_OFFSET_TABLE_)
109 return plabel[0];
110
111 /* Find the first "bl" branch in the offset search list. This is a
112 call to _dl_fixup or a magic branch to fixup at the beginning of the
113 trampoline template. The fixup function does the actual runtime
114 resolution of function descriptors. We only look for "bl" branches
115 with a 17-bit pc-relative displacement. */
116 for (i = 0; i < NOFFSETS; i++)
117 {
118 iptr = (unsigned int *) (got[-2] + fixup_branch_offset[i]);
119 if ((*iptr & 0xfc00e000) == 0xe8000000)
120 break;
121 }
122
123 /* This should not happen... */
124 if (i == NOFFSETS)
125 return ~0;
126
127 /* Extract the 17-bit displacement from the instruction. */
128 iptr += SIGN_EXTEND (GET_FIELD (*iptr, 19, 28) |
129 GET_FIELD (*iptr, 29, 29) << 10 |
130 GET_FIELD (*iptr, 11, 15) << 11 |
131 GET_FIELD (*iptr, 31, 31) << 16, 17);
132
133 /* Build a plabel for an indirect call to _dl_fixup. */
134 fixup_plabel[0] = (unsigned int) iptr + 8; /* address of fixup */
135 fixup_plabel[1] = got[-1]; /* ltp for fixup */
136 fixup = (fixup_t) ((int) fixup_plabel | 3);
137
138 /* Call fixup to resolve the function address. got[1] contains the
139 link_map pointer and plabel[1] the relocation offset. */
140 fixup ((struct link_map *) got[1], plabel[1]);
141
142 return plabel[0];
143 }
144