--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/utilities/elfFuncDescTable.hpp Thu Dec 05 19:19:09 2013 +0100
@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright 2012, 2013 SAP AG. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP
+#define SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP
+
+#if !defined(_WINDOWS) && !defined(__APPLE__)
+
+
+#include "memory/allocation.hpp"
+#include "utilities/decoder.hpp"
+#include "utilities/elfFile.hpp"
+
+/*
+
+On PowerPC-64 (and other architectures like for example IA64) a pointer to a
+function is not just a plain code address, but instead a pointer to a so called
+function descriptor (which is simply a structure containing 3 pointers).
+This fact is also reflected in the ELF ABI for PowerPC-64.
+
+On architectures like x86 or SPARC, the ELF symbol table contains the start
+address and size of an object. So for example for a function object (i.e. type
+'STT_FUNC') the symbol table's 'st_value' and 'st_size' fields directly
+represent the starting address and size of that function. On PPC64 however, the
+symbol table's 'st_value' field only contains an index into another, PPC64
+specific '.opd' (official procedure descriptors) section, while the 'st_size'
+field still holds the size of the corresponding function. In order to get the
+actual start address of a function, it is necessary to read the corresponding
+function descriptor entry in the '.opd' section at the corresponding index and
+extract the start address from there.
+
+That's exactly what this 'ElfFuncDescTable' class is used for. If the HotSpot
+runs on a PPC64 machine, and the corresponding ELF files contains an '.opd'
+section (which is actually mandatory on PPC64) it will be read into an object
+of type 'ElfFuncDescTable' just like the string and symbol table sections.
+Later on, during symbol lookup in 'ElfSymbolTable::lookup()' this function
+descriptor table will be used if available to find the real function address.
+
+All this is how things work today (2013) on contemporary Linux distributions
+(i.e. SLES 10) and new version of GCC (i.e. > 4.0). However there is a history,
+and it goes like this:
+
+In SLES 9 times (sometimes before GCC 3.4) gcc/ld on PPC64 generated two
+entries in the symbol table for every function. The value of the symbol with
+the name of the function was the address of the function descriptor while the
+dot '.' prefixed name was reserved to hold the actual address of that function
+(http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#FUNC-DES).
+
+For a C-function 'foo' this resulted in two symbol table entries like this
+(extracted from the output of 'readelf -a <lib.so>'):
+
+Section Headers:
+ [ 9] .text PROGBITS 0000000000000a20 00000a20
+ 00000000000005a0 0000000000000000 AX 0 0 16
+ [21] .opd PROGBITS 00000000000113b8 000013b8
+ 0000000000000138 0000000000000000 WA 0 0 8
+
+Symbol table '.symtab' contains 86 entries:
+ Num: Value Size Type Bind Vis Ndx Name
+ 76: 00000000000114c0 24 FUNC GLOBAL DEFAULT 21 foo
+ 78: 0000000000000bb0 76 FUNC GLOBAL DEFAULT 9 .foo
+
+You can see now that the '.foo' entry actually points into the '.text' segment
+('Ndx'=9) and its value and size fields represent the functions actual address
+and size. On the other hand, the entry for plain 'foo' points into the '.opd'
+section ('Ndx'=21) and its value and size fields are the index into the '.opd'
+section and the size of the corresponding '.opd' section entry (3 pointers on
+PPC64).
+
+These so called 'dot symbols' were dropped around gcc 3.4 from GCC and BINUTILS,
+see http://gcc.gnu.org/ml/gcc-patches/2004-08/msg00557.html.
+But nevertheless it may still be necessary to support both formats because we
+either run on an old system or because it is possible at any time that functions
+appear in the stack trace which come from old-style libraries.
+
+Therefore we not only have to check for the presence of the function descriptor
+table during symbol lookup in 'ElfSymbolTable::lookup()'. We additionally have
+to check that the symbol table entry references the '.opd' section. Only in
+that case we can resolve the actual function address from there. Otherwise we
+use the plain 'st_value' field from the symbol table as function address. This
+way we can also lookup the symbols in old-style ELF libraries (although we get
+the 'dotted' versions in that case). However, if present, the 'dot' will be
+conditionally removed on PPC64 from the symbol in 'ElfDecoder::demangle()' in
+decoder_linux.cpp.
+
+Notice that we can not reliably get the function address from old-style
+libraries because the 'st_value' field of the symbol table entries which point
+into the '.opd' section denote the size of the corresponding '.opd' entry and
+not that of the corresponding function. This has changed for the symbol table
+entries in new-style libraries as described at the beginning of this
+documentation.
+
+*/
+
+class ElfFuncDescTable: public CHeapObj<mtInternal> {
+ friend class ElfFile;
+ public:
+ ElfFuncDescTable(FILE* file, Elf_Shdr shdr, int index);
+ ~ElfFuncDescTable();
+
+ // return the function address for the function descriptor at 'index' or NULL on error
+ address lookup(Elf_Word index);
+
+ int get_index() { return m_index; };
+
+ NullDecoder::decoder_status get_status() { return m_status; };
+
+ protected:
+ // holds the complete function descriptor section if
+ // we can allocate enough memory
+ address* m_funcDescs;
+
+ // file contains string table
+ FILE* m_file;
+
+ // section header
+ Elf_Shdr m_shdr;
+
+ // The section index of this function descriptor (i.e. '.opd') section in the ELF file
+ int m_index;
+
+ NullDecoder::decoder_status m_status;
+};
+
+#endif // !_WINDOWS && !__APPLE__
+
+#endif // SHARE_VM_UTILITIES_ELF_FUNC_DESC_TABLE_HPP