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The relocInfo.hpp Java example source code
/*
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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#ifndef SHARE_VM_CODE_RELOCINFO_HPP
#define SHARE_VM_CODE_RELOCINFO_HPP
#include "memory/allocation.hpp"
#include "utilities/top.hpp"
class NativeMovConstReg;
// Types in this file:
// relocInfo
// One element of an array of halfwords encoding compressed relocations.
// Also, the source of relocation types (relocInfo::oop_type, ...).
// Relocation
// A flyweight object representing a single relocation.
// It is fully unpacked from the compressed relocation array.
// metadata_Relocation, ... (subclasses of Relocation)
// The location of some type-specific operations (metadata_addr, ...).
// Also, the source of relocation specs (metadata_Relocation::spec, ...).
// oop_Relocation, ... (subclasses of Relocation)
// oops in the code stream (strings, class loaders)
// Also, the source of relocation specs (oop_Relocation::spec, ...).
// RelocationHolder
// A ValueObj type which acts as a union holding a Relocation object.
// Represents a relocation spec passed into a CodeBuffer during assembly.
// RelocIterator
// A StackObj which iterates over the relocations associated with
// a range of code addresses. Can be used to operate a copy of code.
// BoundRelocation
// An _internal_ type shared by packers and unpackers of relocations.
// It pastes together a RelocationHolder with some pointers into
// code and relocInfo streams.
// Notes on relocType:
//
// These hold enough information to read or write a value embedded in
// the instructions of an CodeBlob. They're used to update:
//
// 1) embedded oops (isOop() == true)
// 2) inline caches (isIC() == true)
// 3) runtime calls (isRuntimeCall() == true)
// 4) internal word ref (isInternalWord() == true)
// 5) external word ref (isExternalWord() == true)
//
// when objects move (GC) or if code moves (compacting the code heap).
// They are also used to patch the code (if a call site must change)
//
// A relocInfo is represented in 16 bits:
// 4 bits indicating the relocation type
// 12 bits indicating the offset from the previous relocInfo address
//
// The offsets accumulate along the relocInfo stream to encode the
// address within the CodeBlob, which is named RelocIterator::addr().
// The address of a particular relocInfo always points to the first
// byte of the relevant instruction (and not to any of its subfields
// or embedded immediate constants).
//
// The offset value is scaled appropriately for the target machine.
// (See relocInfo_<arch>.hpp for the offset scaling.)
//
// On some machines, there may also be a "format" field which may provide
// additional information about the format of the instruction stream
// at the corresponding code address. The format value is usually zero.
// Any machine (such as Intel) whose instructions can sometimes contain
// more than one relocatable constant needs format codes to distinguish
// which operand goes with a given relocation.
//
// If the target machine needs N format bits, the offset has 12-N bits,
// the format is encoded between the offset and the type, and the
// relocInfo_<arch>.hpp file has manifest constants for the format codes.
//
// If the type is "data_prefix_tag" then the offset bits are further encoded,
// and in fact represent not a code-stream offset but some inline data.
// The data takes the form of a counted sequence of halfwords, which
// precedes the actual relocation record. (Clients never see it directly.)
// The interpetation of this extra data depends on the relocation type.
//
// On machines that have 32-bit immediate fields, there is usually
// little need for relocation "prefix" data, because the instruction stream
// is a perfectly reasonable place to store the value. On machines in
// which 32-bit values must be "split" across instructions, the relocation
// data is the "true" specification of the value, which is then applied
// to some field of the instruction (22 or 13 bits, on SPARC).
//
// Whenever the location of the CodeBlob changes, any PC-relative
// relocations, and any internal_word_type relocations, must be reapplied.
// After the GC runs, oop_type relocations must be reapplied.
//
//
// Here are meanings of the types:
//
// relocInfo::none -- a filler record
// Value: none
// Instruction: The corresponding code address is ignored
// Data: Any data prefix and format code are ignored
// (This means that any relocInfo can be disabled by setting
// its type to none. See relocInfo::remove.)
//
// relocInfo::oop_type, relocInfo::metadata_type -- a reference to an oop or meta data
// Value: an oop, or else the address (handle) of an oop
// Instruction types: memory (load), set (load address)
// Data: [] an oop stored in 4 bytes of instruction
// [n] n is the index of an oop in the CodeBlob's oop pool
// [[N]n l] and l is a byte offset to be applied to the oop
// [Nn Ll] both index and offset may be 32 bits if necessary
// Here is a special hack, used only by the old compiler:
// [[N]n 00] the value is the __address__ of the nth oop in the pool
// (Note that the offset allows optimal references to class variables.)
//
// relocInfo::internal_word_type -- an address within the same CodeBlob
// relocInfo::section_word_type -- same, but can refer to another section
// Value: an address in the CodeBlob's code or constants section
// Instruction types: memory (load), set (load address)
// Data: [] stored in 4 bytes of instruction
// [[L]l] a relative offset (see [About Offsets] below)
// In the case of section_word_type, the offset is relative to a section
// base address, and the section number (e.g., SECT_INSTS) is encoded
// into the low two bits of the offset L.
//
// relocInfo::external_word_type -- a fixed address in the runtime system
// Value: an address
// Instruction types: memory (load), set (load address)
// Data: [] stored in 4 bytes of instruction
// [n] the index of a "well-known" stub (usual case on RISC)
// [Ll] a 32-bit address
//
// relocInfo::runtime_call_type -- a fixed subroutine in the runtime system
// Value: an address
// Instruction types: PC-relative call (or a PC-relative branch)
// Data: [] stored in 4 bytes of instruction
//
// relocInfo::static_call_type -- a static call
// Value: an CodeBlob, a stub, or a fixup routine
// Instruction types: a call
// Data: []
// The identity of the callee is extracted from debugging information.
// //%note reloc_3
//
// relocInfo::virtual_call_type -- a virtual call site (which includes an inline
// cache)
// Value: an CodeBlob, a stub, the interpreter, or a fixup routine
// Instruction types: a call, plus some associated set-oop instructions
// Data: [] the associated set-oops are adjacent to the call
// [n] n is a relative offset to the first set-oop
// [[N]n l] and l is a limit within which the set-oops occur
// [Nn Ll] both n and l may be 32 bits if necessary
// The identity of the callee is extracted from debugging information.
//
// relocInfo::opt_virtual_call_type -- a virtual call site that is statically bound
//
// Same info as a static_call_type. We use a special type, so the handling of
// virtuals and statics are separated.
//
//
// The offset n points to the first set-oop. (See [About Offsets] below.)
// In turn, the set-oop instruction specifies or contains an oop cell devoted
// exclusively to the IC call, which can be patched along with the call.
//
// The locations of any other set-oops are found by searching the relocation
// information starting at the first set-oop, and continuing until all
// relocations up through l have been inspected. The value l is another
// relative offset. (Both n and l are relative to the call's first byte.)
//
// The limit l of the search is exclusive. However, if it points within
// the call (e.g., offset zero), it is adjusted to point after the call and
// any associated machine-specific delay slot.
//
// Since the offsets could be as wide as 32-bits, these conventions
// put no restrictions whatever upon code reorganization.
//
// The compiler is responsible for ensuring that transition from a clean
// state to a monomorphic compiled state is MP-safe. This implies that
// the system must respond well to intermediate states where a random
// subset of the set-oops has been correctly from the clean state
// upon entry to the VEP of the compiled method. In the case of a
// machine (Intel) with a single set-oop instruction, the 32-bit
// immediate field must not straddle a unit of memory coherence.
// //%note reloc_3
//
// relocInfo::static_stub_type -- an extra stub for each static_call_type
// Value: none
// Instruction types: a virtual call: { set_oop; jump; }
// Data: [[N]n] the offset of the associated static_call reloc
// This stub becomes the target of a static call which must be upgraded
// to a virtual call (because the callee is interpreted).
// See [About Offsets] below.
// //%note reloc_2
//
// For example:
//
// INSTRUCTIONS RELOC: TYPE PREFIX DATA
// ------------ ---- -----------
// sethi %hi(myObject), R oop_type [n(myObject)]
// ld [R+%lo(myObject)+fldOffset], R2 oop_type [n(myObject) fldOffset]
// add R2, 1, R2
// st R2, [R+%lo(myObject)+fldOffset] oop_type [n(myObject) fldOffset]
//%note reloc_1
//
// This uses 4 instruction words, 8 relocation halfwords,
// and an entry (which is sharable) in the CodeBlob's oop pool,
// for a total of 36 bytes.
//
// Note that the compiler is responsible for ensuring the "fldOffset" when
// added to "%lo(myObject)" does not overflow the immediate fields of the
// memory instructions.
//
//
// [About Offsets] Relative offsets are supplied to this module as
// positive byte offsets, but they may be internally stored scaled
// and/or negated, depending on what is most compact for the target
// system. Since the object pointed to by the offset typically
// precedes the relocation address, it is profitable to store
// these negative offsets as positive numbers, but this decision
// is internal to the relocation information abstractions.
//
class Relocation;
class CodeBuffer;
class CodeSection;
class RelocIterator;
class relocInfo VALUE_OBJ_CLASS_SPEC {
friend class RelocIterator;
public:
enum relocType {
none = 0, // Used when no relocation should be generated
oop_type = 1, // embedded oop
virtual_call_type = 2, // a standard inline cache call for a virtual send
opt_virtual_call_type = 3, // a virtual call that has been statically bound (i.e., no IC cache)
static_call_type = 4, // a static send
static_stub_type = 5, // stub-entry for static send (takes care of interpreter case)
runtime_call_type = 6, // call to fixed external routine
external_word_type = 7, // reference to fixed external address
internal_word_type = 8, // reference within the current code blob
section_word_type = 9, // internal, but a cross-section reference
poll_type = 10, // polling instruction for safepoints
poll_return_type = 11, // polling instruction for safepoints at return
metadata_type = 12, // metadata that used to be oops
yet_unused_type_1 = 13, // Still unused
yet_unused_type_2 = 14, // Still unused
data_prefix_tag = 15, // tag for a prefix (carries data arguments)
type_mask = 15 // A mask which selects only the above values
};
protected:
unsigned short _value;
enum RawBitsToken { RAW_BITS };
relocInfo(relocType type, RawBitsToken ignore, int bits)
: _value((type << nontype_width) + bits) { }
relocInfo(relocType type, RawBitsToken ignore, int off, int f)
: _value((type << nontype_width) + (off / (unsigned)offset_unit) + (f << offset_width)) { }
public:
// constructor
relocInfo(relocType type, int offset, int format = 0)
#ifndef ASSERT
{
(*this) = relocInfo(type, RAW_BITS, offset, format);
}
#else
// Put a bunch of assertions out-of-line.
;
#endif
#define APPLY_TO_RELOCATIONS(visitor) \
visitor(oop) \
visitor(metadata) \
visitor(virtual_call) \
visitor(opt_virtual_call) \
visitor(static_call) \
visitor(static_stub) \
visitor(runtime_call) \
visitor(external_word) \
visitor(internal_word) \
visitor(poll) \
visitor(poll_return) \
visitor(section_word) \
public:
enum {
value_width = sizeof(unsigned short) * BitsPerByte,
type_width = 4, // == log2(type_mask+1)
nontype_width = value_width - type_width,
datalen_width = nontype_width-1,
datalen_tag = 1 << datalen_width, // or-ed into _value
datalen_limit = 1 << datalen_width,
datalen_mask = (1 << datalen_width)-1
};
// accessors
public:
relocType type() const { return (relocType)((unsigned)_value >> nontype_width); }
int format() const { return format_mask==0? 0: format_mask &
((unsigned)_value >> offset_width); }
int addr_offset() const { assert(!is_prefix(), "must have offset");
return (_value & offset_mask)*offset_unit; }
protected:
const short* data() const { assert(is_datalen(), "must have data");
return (const short*)(this + 1); }
int datalen() const { assert(is_datalen(), "must have data");
return (_value & datalen_mask); }
int immediate() const { assert(is_immediate(), "must have immed");
return (_value & datalen_mask); }
public:
static int addr_unit() { return offset_unit; }
static int offset_limit() { return (1 << offset_width) * offset_unit; }
void set_type(relocType type);
void set_format(int format);
void remove() { set_type(none); }
protected:
bool is_none() const { return type() == none; }
bool is_prefix() const { return type() == data_prefix_tag; }
bool is_datalen() const { assert(is_prefix(), "must be prefix");
return (_value & datalen_tag) != 0; }
bool is_immediate() const { assert(is_prefix(), "must be prefix");
return (_value & datalen_tag) == 0; }
public:
// Occasionally records of type relocInfo::none will appear in the stream.
// We do not bother to filter these out, but clients should ignore them.
// These records serve as "filler" in three ways:
// - to skip large spans of unrelocated code (this is rare)
// - to pad out the relocInfo array to the required oop alignment
// - to disable old relocation information which is no longer applicable
inline friend relocInfo filler_relocInfo();
// Every non-prefix relocation may be preceded by at most one prefix,
// which supplies 1 or more halfwords of associated data. Conventionally,
// an int is represented by 0, 1, or 2 halfwords, depending on how
// many bits are required to represent the value. (In addition,
// if the sole halfword is a 10-bit unsigned number, it is made
// "immediate" in the prefix header word itself. This optimization
// is invisible outside this module.)
inline friend relocInfo prefix_relocInfo(int datalen = 0);
protected:
// an immediate relocInfo optimizes a prefix with one 10-bit unsigned value
static relocInfo immediate_relocInfo(int data0) {
assert(fits_into_immediate(data0), "data0 in limits");
return relocInfo(relocInfo::data_prefix_tag, RAW_BITS, data0);
}
static bool fits_into_immediate(int data0) {
return (data0 >= 0 && data0 < datalen_limit);
}
public:
// Support routines for compilers.
// This routine takes an infant relocInfo (unprefixed) and
// edits in its prefix, if any. It also updates dest.locs_end.
void initialize(CodeSection* dest, Relocation* reloc);
// This routine updates a prefix and returns the limit pointer.
// It tries to compress the prefix from 32 to 16 bits, and if
// successful returns a reduced "prefix_limit" pointer.
relocInfo* finish_prefix(short* prefix_limit);
// bit-packers for the data array:
// As it happens, the bytes within the shorts are ordered natively,
// but the shorts within the word are ordered big-endian.
// This is an arbitrary choice, made this way mainly to ease debugging.
static int data0_from_int(jint x) { return x >> value_width; }
static int data1_from_int(jint x) { return (short)x; }
static jint jint_from_data(short* data) {
return (data[0] << value_width) + (unsigned short)data[1];
}
static jint short_data_at(int n, short* data, int datalen) {
return datalen > n ? data[n] : 0;
}
static jint jint_data_at(int n, short* data, int datalen) {
return datalen > n+1 ? jint_from_data(&data[n]) : short_data_at(n, data, datalen);
}
// Update methods for relocation information
// (since code is dynamically patched, we also need to dynamically update the relocation info)
// Both methods takes old_type, so it is able to performe sanity checks on the information removed.
static void change_reloc_info_for_address(RelocIterator *itr, address pc, relocType old_type, relocType new_type);
static void remove_reloc_info_for_address(RelocIterator *itr, address pc, relocType old_type);
// Machine dependent stuff
#ifdef TARGET_ARCH_x86
# include "relocInfo_x86.hpp"
#endif
#ifdef TARGET_ARCH_sparc
# include "relocInfo_sparc.hpp"
#endif
#ifdef TARGET_ARCH_zero
# include "relocInfo_zero.hpp"
#endif
#ifdef TARGET_ARCH_arm
# include "relocInfo_arm.hpp"
#endif
#ifdef TARGET_ARCH_ppc
# include "relocInfo_ppc.hpp"
#endif
protected:
// Derived constant, based on format_width which is PD:
enum {
offset_width = nontype_width - format_width,
offset_mask = (1<
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