s390x/pci: use a PCI Group structure
[qemu.git] / exec-vary.c
1 /*
2 * Variable page size handling
3 *
4 * Copyright (c) 2003 Fabrice Bellard
5 *
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2 of the License, or (at your option) any later version.
10 *
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
18 */
19
20 #include "qemu/osdep.h"
21 #include "qemu-common.h"
22
23 #define IN_EXEC_VARY 1
24
25 #include "exec/exec-all.h"
26
27 #ifdef TARGET_PAGE_BITS_VARY
28 # ifdef CONFIG_ATTRIBUTE_ALIAS
29 /*
30 * We want to declare the "target_page" variable as const, which tells
31 * the compiler that it can cache any value that it reads across calls.
32 * This avoids multiple assertions and multiple reads within any one user.
33 *
34 * This works because we finish initializing the data before we ever read
35 * from the "target_page" symbol.
36 *
37 * This also requires that we have a non-constant symbol by which we can
38 * perform the actual initialization, and which forces the data to be
39 * allocated within writable memory. Thus "init_target_page", and we use
40 * that symbol exclusively in the two functions that initialize this value.
41 *
42 * The "target_page" symbol is created as an alias of "init_target_page".
43 */
44 static TargetPageBits init_target_page;
45
46 /*
47 * Note that this is *not* a redundant decl, this is the definition of
48 * the "target_page" symbol. The syntax for this definition requires
49 * the use of the extern keyword. This seems to be a GCC bug in
50 * either the syntax for the alias attribute or in -Wredundant-decls.
51 *
52 * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91765
53 */
54 # pragma GCC diagnostic push
55 # pragma GCC diagnostic ignored "-Wredundant-decls"
56
57 extern const TargetPageBits target_page
58 __attribute__((alias("init_target_page")));
59
60 # pragma GCC diagnostic pop
61 # else
62 /*
63 * When aliases are not supported then we force two different declarations,
64 * by way of suppressing the header declaration with IN_EXEC_VARY.
65 * We assume that on such an old compiler, LTO cannot be used, and so the
66 * compiler cannot not detect the mismatched declarations, and all is well.
67 */
68 TargetPageBits target_page;
69 # define init_target_page target_page
70 # endif
71 #endif
72
73 bool set_preferred_target_page_bits(int bits)
74 {
75 /*
76 * The target page size is the lowest common denominator for all
77 * the CPUs in the system, so we can only make it smaller, never
78 * larger. And we can't make it smaller once we've committed to
79 * a particular size.
80 */
81 #ifdef TARGET_PAGE_BITS_VARY
82 assert(bits >= TARGET_PAGE_BITS_MIN);
83 if (init_target_page.bits == 0 || init_target_page.bits > bits) {
84 if (init_target_page.decided) {
85 return false;
86 }
87 init_target_page.bits = bits;
88 }
89 #endif
90 return true;
91 }
92
93 void finalize_target_page_bits(void)
94 {
95 #ifdef TARGET_PAGE_BITS_VARY
96 if (init_target_page.bits == 0) {
97 init_target_page.bits = TARGET_PAGE_BITS_MIN;
98 }
99 init_target_page.mask = (target_long)-1 << init_target_page.bits;
100 init_target_page.decided = true;
101
102 /*
103 * For the benefit of an -flto build, prevent the compiler from
104 * hoisting a read from target_page before we finish initializing.
105 */
106 barrier();
107 #endif
108 }