1 /* Subroutine for function pointer canonicalization on PA-RISC with ELF32.
2 Copyright (C) 2002-2019 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 volatile unsigned int *plabel;
80 unsigned int *got, *iptr, reloc_offset;
81 int i;
82
83 /* -1 and page 0 are special. -1 is used in crtend to mark the end of
84 a list of function pointers. Also return immediately if the plabel
85 bit is not set in the function pointer. In this case, the function
86 pointer points directly to the function. */
87 if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2))
88 return (unsigned int) fptr;
89
90 /* The function pointer points to a function descriptor (plabel). If
91 the plabel hasn't been resolved, the first word of the plabel points
92 to the entry of the PLT stub just before the global offset table.
93 The second word in the plabel contains the relocation offset for the
94 function. */
95 plabel = (volatile unsigned int *) ((unsigned int) fptr & ~3);
96 if (!_dl_read_access_allowed ((unsigned int)plabel))
97 return (unsigned int) fptr;
98
99 /* Load first word of candidate descriptor. It should be a pointer
100 with word alignment and point to memory that can be read. */
101 got = (unsigned int *) plabel[0];
102 if (((unsigned int) got & 3) != 0
103 || !_dl_read_access_allowed ((unsigned int)got))
104 return (unsigned int) fptr;
105
106 /* We need to load the relocation offset before the function address. */
107 reloc_offset = plabel[1];
108 __sync_synchronize();
109 got = (unsigned int *) (plabel[0] + GOT_FROM_PLT_STUB);
110
111 /* Return the address of the function if the plabel has been resolved. */
112 if (got != &_GLOBAL_OFFSET_TABLE_)
113 return plabel[0];
114
115 /* Find the first "bl" branch in the offset search list. This is a
116 call to _dl_fixup or a magic branch to fixup at the beginning of the
117 trampoline template. The fixup function does the actual runtime
118 resolution of function descriptors. We only look for "bl" branches
119 with a 17-bit pc-relative displacement. */
120 for (i = 0; i < NOFFSETS; i++)
121 {
122 iptr = (unsigned int *) (got[-2] + fixup_branch_offset[i]);
123 if ((*iptr & 0xfc00e000) == 0xe8000000)
124 break;
125 }
126
127 /* This should not happen... */
128 if (i == NOFFSETS)
129 return ~0;
130
131 /* Extract the 17-bit displacement from the instruction. */
132 iptr += SIGN_EXTEND (GET_FIELD (*iptr, 19, 28) |
133 GET_FIELD (*iptr, 29, 29) << 10 |
134 GET_FIELD (*iptr, 11, 15) << 11 |
135 GET_FIELD (*iptr, 31, 31) << 16, 17);
136
137 /* Build a plabel for an indirect call to _dl_fixup. */
138 fixup_plabel[0] = (unsigned int) iptr + 8; /* address of fixup */
139 fixup_plabel[1] = got[-1]; /* ltp for fixup */
140 fixup = (fixup_t) ((int) fixup_plabel | 2);
141
142 /* Call fixup to resolve the function address. got[1] contains the
143 link_map pointer and plabel[1] the relocation offset. */
144 fixup ((struct link_map *) got[1], reloc_offset);
145
146 return plabel[0];
147 }
148