Mercurial > hg > truffle
comparison src/share/vm/utilities/elfFuncDescTable.hpp @ 14441:e7cbc95179c4
8019929: PPC64 (part 107): Extend ELF-decoder to support PPC64 function descriptor tables
Summary: Extend ELF-decoder to support PPC64 function descriptor tables
Reviewed-by: kvn, zgu
author | simonis |
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date | Thu, 05 Dec 2013 19:19:09 +0100 |
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14440:41b780b43b74 | 14441:e7cbc95179c4 |
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1 /* | |
2 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. | |
3 * Copyright 2012, 2013 SAP AG. All rights reserved. | |
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
5 * | |
6 * This code is free software; you can redistribute it and/or modify it | |
7 * under the terms of the GNU General Public License version 2 only, as | |
8 * published by the Free Software Foundation. | |
9 * | |
10 * This code is distributed in the hope that it will be useful, but WITHOUT | |
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
13 * version 2 for more details (a copy is included in the LICENSE file that | |
14 * accompanied this code). | |
15 * | |
16 * You should have received a copy of the GNU General Public License version | |
17 * 2 along with this work; if not, write to the Free Software Foundation, | |
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
19 * | |
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
21 * or visit www.oracle.com if you need additional information or have any | |
22 * questions. | |
23 * | |
24 */ | |
25 | |
26 #ifndef SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP | |
27 #define SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP | |
28 | |
29 #if !defined(_WINDOWS) && !defined(__APPLE__) | |
30 | |
31 | |
32 #include "memory/allocation.hpp" | |
33 #include "utilities/decoder.hpp" | |
34 #include "utilities/elfFile.hpp" | |
35 | |
36 /* | |
37 | |
38 On PowerPC-64 (and other architectures like for example IA64) a pointer to a | |
39 function is not just a plain code address, but instead a pointer to a so called | |
40 function descriptor (which is simply a structure containing 3 pointers). | |
41 This fact is also reflected in the ELF ABI for PowerPC-64. | |
42 | |
43 On architectures like x86 or SPARC, the ELF symbol table contains the start | |
44 address and size of an object. So for example for a function object (i.e. type | |
45 'STT_FUNC') the symbol table's 'st_value' and 'st_size' fields directly | |
46 represent the starting address and size of that function. On PPC64 however, the | |
47 symbol table's 'st_value' field only contains an index into another, PPC64 | |
48 specific '.opd' (official procedure descriptors) section, while the 'st_size' | |
49 field still holds the size of the corresponding function. In order to get the | |
50 actual start address of a function, it is necessary to read the corresponding | |
51 function descriptor entry in the '.opd' section at the corresponding index and | |
52 extract the start address from there. | |
53 | |
54 That's exactly what this 'ElfFuncDescTable' class is used for. If the HotSpot | |
55 runs on a PPC64 machine, and the corresponding ELF files contains an '.opd' | |
56 section (which is actually mandatory on PPC64) it will be read into an object | |
57 of type 'ElfFuncDescTable' just like the string and symbol table sections. | |
58 Later on, during symbol lookup in 'ElfSymbolTable::lookup()' this function | |
59 descriptor table will be used if available to find the real function address. | |
60 | |
61 All this is how things work today (2013) on contemporary Linux distributions | |
62 (i.e. SLES 10) and new version of GCC (i.e. > 4.0). However there is a history, | |
63 and it goes like this: | |
64 | |
65 In SLES 9 times (sometimes before GCC 3.4) gcc/ld on PPC64 generated two | |
66 entries in the symbol table for every function. The value of the symbol with | |
67 the name of the function was the address of the function descriptor while the | |
68 dot '.' prefixed name was reserved to hold the actual address of that function | |
69 (http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#FUNC-DES). | |
70 | |
71 For a C-function 'foo' this resulted in two symbol table entries like this | |
72 (extracted from the output of 'readelf -a <lib.so>'): | |
73 | |
74 Section Headers: | |
75 [ 9] .text PROGBITS 0000000000000a20 00000a20 | |
76 00000000000005a0 0000000000000000 AX 0 0 16 | |
77 [21] .opd PROGBITS 00000000000113b8 000013b8 | |
78 0000000000000138 0000000000000000 WA 0 0 8 | |
79 | |
80 Symbol table '.symtab' contains 86 entries: | |
81 Num: Value Size Type Bind Vis Ndx Name | |
82 76: 00000000000114c0 24 FUNC GLOBAL DEFAULT 21 foo | |
83 78: 0000000000000bb0 76 FUNC GLOBAL DEFAULT 9 .foo | |
84 | |
85 You can see now that the '.foo' entry actually points into the '.text' segment | |
86 ('Ndx'=9) and its value and size fields represent the functions actual address | |
87 and size. On the other hand, the entry for plain 'foo' points into the '.opd' | |
88 section ('Ndx'=21) and its value and size fields are the index into the '.opd' | |
89 section and the size of the corresponding '.opd' section entry (3 pointers on | |
90 PPC64). | |
91 | |
92 These so called 'dot symbols' were dropped around gcc 3.4 from GCC and BINUTILS, | |
93 see http://gcc.gnu.org/ml/gcc-patches/2004-08/msg00557.html. | |
94 But nevertheless it may still be necessary to support both formats because we | |
95 either run on an old system or because it is possible at any time that functions | |
96 appear in the stack trace which come from old-style libraries. | |
97 | |
98 Therefore we not only have to check for the presence of the function descriptor | |
99 table during symbol lookup in 'ElfSymbolTable::lookup()'. We additionally have | |
100 to check that the symbol table entry references the '.opd' section. Only in | |
101 that case we can resolve the actual function address from there. Otherwise we | |
102 use the plain 'st_value' field from the symbol table as function address. This | |
103 way we can also lookup the symbols in old-style ELF libraries (although we get | |
104 the 'dotted' versions in that case). However, if present, the 'dot' will be | |
105 conditionally removed on PPC64 from the symbol in 'ElfDecoder::demangle()' in | |
106 decoder_linux.cpp. | |
107 | |
108 Notice that we can not reliably get the function address from old-style | |
109 libraries because the 'st_value' field of the symbol table entries which point | |
110 into the '.opd' section denote the size of the corresponding '.opd' entry and | |
111 not that of the corresponding function. This has changed for the symbol table | |
112 entries in new-style libraries as described at the beginning of this | |
113 documentation. | |
114 | |
115 */ | |
116 | |
117 class ElfFuncDescTable: public CHeapObj<mtInternal> { | |
118 friend class ElfFile; | |
119 public: | |
120 ElfFuncDescTable(FILE* file, Elf_Shdr shdr, int index); | |
121 ~ElfFuncDescTable(); | |
122 | |
123 // return the function address for the function descriptor at 'index' or NULL on error | |
124 address lookup(Elf_Word index); | |
125 | |
126 int get_index() { return m_index; }; | |
127 | |
128 NullDecoder::decoder_status get_status() { return m_status; }; | |
129 | |
130 protected: | |
131 // holds the complete function descriptor section if | |
132 // we can allocate enough memory | |
133 address* m_funcDescs; | |
134 | |
135 // file contains string table | |
136 FILE* m_file; | |
137 | |
138 // section header | |
139 Elf_Shdr m_shdr; | |
140 | |
141 // The section index of this function descriptor (i.e. '.opd') section in the ELF file | |
142 int m_index; | |
143 | |
144 NullDecoder::decoder_status m_status; | |
145 }; | |
146 | |
147 #endif // !_WINDOWS && !__APPLE__ | |
148 | |
149 #endif // SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP |