Mercurial > jdk8-mips64-public > hotspot / annotate
src/share/vm/utilities/elfFuncDescTable.hpp@f90c822e73f8 (annotated)
src/share/vm/utilities/elfFuncDescTable.hpp
Wed, 27 Apr 2016 01:25:04 +0800
- author
- aoqi
- date
- Wed, 27 Apr 2016 01:25:04 +0800
- changeset 0
- f90c822e73f8
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http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/
changeset: 6782:28b50d07f6f8
tag: jdk8u25-b17
| aoqi@0 | 1 | /* |
| aoqi@0 | 2 | * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. |
| aoqi@0 | 3 | * Copyright 2012, 2013 SAP AG. All rights reserved. |
| aoqi@0 | 4 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| aoqi@0 | 5 | * |
| aoqi@0 | 6 | * This code is free software; you can redistribute it and/or modify it |
| aoqi@0 | 7 | * under the terms of the GNU General Public License version 2 only, as |
| aoqi@0 | 8 | * published by the Free Software Foundation. |
| aoqi@0 | 9 | * |
| aoqi@0 | 10 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| aoqi@0 | 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| aoqi@0 | 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| aoqi@0 | 13 | * version 2 for more details (a copy is included in the LICENSE file that |
| aoqi@0 | 14 | * accompanied this code). |
| aoqi@0 | 15 | * |
| aoqi@0 | 16 | * You should have received a copy of the GNU General Public License version |
| aoqi@0 | 17 | * 2 along with this work; if not, write to the Free Software Foundation, |
| aoqi@0 | 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| aoqi@0 | 19 | * |
| aoqi@0 | 20 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| aoqi@0 | 21 | * or visit www.oracle.com if you need additional information or have any |
| aoqi@0 | 22 | * questions. |
| aoqi@0 | 23 | * |
| aoqi@0 | 24 | */ |
| aoqi@0 | 25 | |
| aoqi@0 | 26 | #ifndef SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP |
| aoqi@0 | 27 | #define SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP |
| aoqi@0 | 28 | |
| aoqi@0 | 29 | #if !defined(_WINDOWS) && !defined(__APPLE__) |
| aoqi@0 | 30 | |
| aoqi@0 | 31 | |
| aoqi@0 | 32 | #include "memory/allocation.hpp" |
| aoqi@0 | 33 | #include "utilities/decoder.hpp" |
| aoqi@0 | 34 | #include "utilities/elfFile.hpp" |
| aoqi@0 | 35 | |
| aoqi@0 | 36 | /* |
| aoqi@0 | 37 | |
| aoqi@0 | 38 | On PowerPC-64 (and other architectures like for example IA64) a pointer to a |
| aoqi@0 | 39 | function is not just a plain code address, but instead a pointer to a so called |
| aoqi@0 | 40 | function descriptor (which is simply a structure containing 3 pointers). |
| aoqi@0 | 41 | This fact is also reflected in the ELF ABI for PowerPC-64. |
| aoqi@0 | 42 | |
| aoqi@0 | 43 | On architectures like x86 or SPARC, the ELF symbol table contains the start |
| aoqi@0 | 44 | address and size of an object. So for example for a function object (i.e. type |
| aoqi@0 | 45 | 'STT_FUNC') the symbol table's 'st_value' and 'st_size' fields directly |
| aoqi@0 | 46 | represent the starting address and size of that function. On PPC64 however, the |
| aoqi@0 | 47 | symbol table's 'st_value' field only contains an index into another, PPC64 |
| aoqi@0 | 48 | specific '.opd' (official procedure descriptors) section, while the 'st_size' |
| aoqi@0 | 49 | field still holds the size of the corresponding function. In order to get the |
| aoqi@0 | 50 | actual start address of a function, it is necessary to read the corresponding |
| aoqi@0 | 51 | function descriptor entry in the '.opd' section at the corresponding index and |
| aoqi@0 | 52 | extract the start address from there. |
| aoqi@0 | 53 | |
| aoqi@0 | 54 | That's exactly what this 'ElfFuncDescTable' class is used for. If the HotSpot |
| aoqi@0 | 55 | runs on a PPC64 machine, and the corresponding ELF files contains an '.opd' |
| aoqi@0 | 56 | section (which is actually mandatory on PPC64) it will be read into an object |
| aoqi@0 | 57 | of type 'ElfFuncDescTable' just like the string and symbol table sections. |
| aoqi@0 | 58 | Later on, during symbol lookup in 'ElfSymbolTable::lookup()' this function |
| aoqi@0 | 59 | descriptor table will be used if available to find the real function address. |
| aoqi@0 | 60 | |
| aoqi@0 | 61 | All this is how things work today (2013) on contemporary Linux distributions |
| aoqi@0 | 62 | (i.e. SLES 10) and new version of GCC (i.e. > 4.0). However there is a history, |
| aoqi@0 | 63 | and it goes like this: |
| aoqi@0 | 64 | |
| aoqi@0 | 65 | In SLES 9 times (sometimes before GCC 3.4) gcc/ld on PPC64 generated two |
| aoqi@0 | 66 | entries in the symbol table for every function. The value of the symbol with |
| aoqi@0 | 67 | the name of the function was the address of the function descriptor while the |
| aoqi@0 | 68 | dot '.' prefixed name was reserved to hold the actual address of that function |
| aoqi@0 | 69 | (http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#FUNC-DES). |
| aoqi@0 | 70 | |
| aoqi@0 | 71 | For a C-function 'foo' this resulted in two symbol table entries like this |
| aoqi@0 | 72 | (extracted from the output of 'readelf -a <lib.so>'): |
| aoqi@0 | 73 | |
| aoqi@0 | 74 | Section Headers: |
| aoqi@0 | 75 | [ 9] .text PROGBITS 0000000000000a20 00000a20 |
| aoqi@0 | 76 | 00000000000005a0 0000000000000000 AX 0 0 16 |
| aoqi@0 | 77 | [21] .opd PROGBITS 00000000000113b8 000013b8 |
| aoqi@0 | 78 | 0000000000000138 0000000000000000 WA 0 0 8 |
| aoqi@0 | 79 | |
| aoqi@0 | 80 | Symbol table '.symtab' contains 86 entries: |
| aoqi@0 | 81 | Num: Value Size Type Bind Vis Ndx Name |
| aoqi@0 | 82 | 76: 00000000000114c0 24 FUNC GLOBAL DEFAULT 21 foo |
| aoqi@0 | 83 | 78: 0000000000000bb0 76 FUNC GLOBAL DEFAULT 9 .foo |
| aoqi@0 | 84 | |
| aoqi@0 | 85 | You can see now that the '.foo' entry actually points into the '.text' segment |
| aoqi@0 | 86 | ('Ndx'=9) and its value and size fields represent the functions actual address |
| aoqi@0 | 87 | and size. On the other hand, the entry for plain 'foo' points into the '.opd' |
| aoqi@0 | 88 | section ('Ndx'=21) and its value and size fields are the index into the '.opd' |
| aoqi@0 | 89 | section and the size of the corresponding '.opd' section entry (3 pointers on |
| aoqi@0 | 90 | PPC64). |
| aoqi@0 | 91 | |
| aoqi@0 | 92 | These so called 'dot symbols' were dropped around gcc 3.4 from GCC and BINUTILS, |
| aoqi@0 | 93 | see http://gcc.gnu.org/ml/gcc-patches/2004-08/msg00557.html. |
| aoqi@0 | 94 | But nevertheless it may still be necessary to support both formats because we |
| aoqi@0 | 95 | either run on an old system or because it is possible at any time that functions |
| aoqi@0 | 96 | appear in the stack trace which come from old-style libraries. |
| aoqi@0 | 97 | |
| aoqi@0 | 98 | Therefore we not only have to check for the presence of the function descriptor |
| aoqi@0 | 99 | table during symbol lookup in 'ElfSymbolTable::lookup()'. We additionally have |
| aoqi@0 | 100 | to check that the symbol table entry references the '.opd' section. Only in |
| aoqi@0 | 101 | that case we can resolve the actual function address from there. Otherwise we |
| aoqi@0 | 102 | use the plain 'st_value' field from the symbol table as function address. This |
| aoqi@0 | 103 | way we can also lookup the symbols in old-style ELF libraries (although we get |
| aoqi@0 | 104 | the 'dotted' versions in that case). However, if present, the 'dot' will be |
| aoqi@0 | 105 | conditionally removed on PPC64 from the symbol in 'ElfDecoder::demangle()' in |
| aoqi@0 | 106 | decoder_linux.cpp. |
| aoqi@0 | 107 | |
| aoqi@0 | 108 | Notice that we can not reliably get the function address from old-style |
| aoqi@0 | 109 | libraries because the 'st_value' field of the symbol table entries which point |
| aoqi@0 | 110 | into the '.opd' section denote the size of the corresponding '.opd' entry and |
| aoqi@0 | 111 | not that of the corresponding function. This has changed for the symbol table |
| aoqi@0 | 112 | entries in new-style libraries as described at the beginning of this |
| aoqi@0 | 113 | documentation. |
| aoqi@0 | 114 | |
| aoqi@0 | 115 | */ |
| aoqi@0 | 116 | |
| aoqi@0 | 117 | class ElfFuncDescTable: public CHeapObj<mtInternal> { |
| aoqi@0 | 118 | friend class ElfFile; |
| aoqi@0 | 119 | public: |
| aoqi@0 | 120 | ElfFuncDescTable(FILE* file, Elf_Shdr shdr, int index); |
| aoqi@0 | 121 | ~ElfFuncDescTable(); |
| aoqi@0 | 122 | |
| aoqi@0 | 123 | // return the function address for the function descriptor at 'index' or NULL on error |
| aoqi@0 | 124 | address lookup(Elf_Word index); |
| aoqi@0 | 125 | |
| aoqi@0 | 126 | int get_index() { return m_index; }; |
| aoqi@0 | 127 | |
| aoqi@0 | 128 | NullDecoder::decoder_status get_status() { return m_status; }; |
| aoqi@0 | 129 | |
| aoqi@0 | 130 | protected: |
| aoqi@0 | 131 | // holds the complete function descriptor section if |
| aoqi@0 | 132 | // we can allocate enough memory |
| aoqi@0 | 133 | address* m_funcDescs; |
| aoqi@0 | 134 | |
| aoqi@0 | 135 | // file contains string table |
| aoqi@0 | 136 | FILE* m_file; |
| aoqi@0 | 137 | |
| aoqi@0 | 138 | // section header |
| aoqi@0 | 139 | Elf_Shdr m_shdr; |
| aoqi@0 | 140 | |
| aoqi@0 | 141 | // The section index of this function descriptor (i.e. '.opd') section in the ELF file |
| aoqi@0 | 142 | int m_index; |
| aoqi@0 | 143 | |
| aoqi@0 | 144 | NullDecoder::decoder_status m_status; |
| aoqi@0 | 145 | }; |
| aoqi@0 | 146 | |
| aoqi@0 | 147 | #endif // !_WINDOWS && !__APPLE__ |
| aoqi@0 | 148 | |
| aoqi@0 | 149 | #endif // SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP |
