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llvm-project/llvm/lib/CodeGen/AsmPrinter/DIEHash.cpp

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//===-- llvm/CodeGen/DIEHash.cpp - Dwarf Hashing Framework ----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains support for DWARF4 hashing of DIEs.
//
//===----------------------------------------------------------------------===//
#include "DIEHash.h"
#include "ByteStreamer.h"
#include "DwarfDebug.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/DIE.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "dwarfdebug"
/// Grabs the string in whichever attribute is passed in and returns
/// a reference to it.
static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) {
// Iterate through all the attributes until we find the one we're
// looking for, if we can't find it return an empty string.
for (const auto &V : Die.values())
if (V.getAttribute() == Attr)
return V.getDIEString().getString();
return StringRef("");
}
/// Adds the string in \p Str to the hash. This also hashes
/// a trailing NULL with the string.
void DIEHash::addString(StringRef Str) {
LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");
Hash.update(Str);
Hash.update(makeArrayRef((uint8_t)'\0'));
}
// FIXME: The LEB128 routines are copied and only slightly modified out of
// LEB128.h.
/// Adds the unsigned in \p Value to the hash encoded as a ULEB128.
void DIEHash::addULEB128(uint64_t Value) {
LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
do {
uint8_t Byte = Value & 0x7f;
Value >>= 7;
if (Value != 0)
Byte |= 0x80; // Mark this byte to show that more bytes will follow.
Hash.update(Byte);
} while (Value != 0);
}
void DIEHash::addSLEB128(int64_t Value) {
LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
bool More;
do {
uint8_t Byte = Value & 0x7f;
Value >>= 7;
More = !((((Value == 0) && ((Byte & 0x40) == 0)) ||
((Value == -1) && ((Byte & 0x40) != 0))));
if (More)
Byte |= 0x80; // Mark this byte to show that more bytes will follow.
Hash.update(Byte);
} while (More);
}
/// Including \p Parent adds the context of Parent to the hash..
void DIEHash::addParentContext(const DIE &Parent) {
LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");
// [7.27.2] For each surrounding type or namespace beginning with the
// outermost such construct...
SmallVector<const DIE *, 1> Parents;
const DIE *Cur = &Parent;
while (Cur->getParent()) {
Parents.push_back(Cur);
Cur = Cur->getParent();
}
assert(Cur->getTag() == dwarf::DW_TAG_compile_unit ||
Cur->getTag() == dwarf::DW_TAG_type_unit);
// Reverse iterate over our list to go from the outermost construct to the
// innermost.
for (SmallVectorImpl<const DIE *>::reverse_iterator I = Parents.rbegin(),
E = Parents.rend();
I != E; ++I) {
const DIE &Die = **I;
// ... Append the letter "C" to the sequence...
addULEB128('C');
// ... Followed by the DWARF tag of the construct...
addULEB128(Die.getTag());
// ... Then the name, taken from the DW_AT_name attribute.
StringRef Name = getDIEStringAttr(Die, dwarf::DW_AT_name);
LLVM_DEBUG(dbgs() << "... adding context: " << Name << "\n");
if (!Name.empty())
addString(Name);
}
}
// Collect all of the attributes for a particular DIE in single structure.
void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) {
for (const auto &V : Die.values()) {
LLVM_DEBUG(dbgs() << "Attribute: "
<< dwarf::AttributeString(V.getAttribute())
<< " added.\n");
switch (V.getAttribute()) {
#define HANDLE_DIE_HASH_ATTR(NAME) \
case dwarf::NAME: \
Attrs.NAME = V; \
break;
#include "DIEHashAttributes.def"
default:
break;
}
}
}
void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute,
const DIE &Entry, StringRef Name) {
// append the letter 'N'
addULEB128('N');
// the DWARF attribute code (DW_AT_type or DW_AT_friend),
addULEB128(Attribute);
// the context of the tag,
if (const DIE *Parent = Entry.getParent())
addParentContext(*Parent);
// the letter 'E',
addULEB128('E');
// and the name of the type.
addString(Name);
// Currently DW_TAG_friends are not used by Clang, but if they do become so,
// here's the relevant spec text to implement:
//
// For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram,
// the context is omitted and the name to be used is the ABI-specific name
// of the subprogram (e.g., the mangled linker name).
}
void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute,
unsigned DieNumber) {
// a) If T is in the list of [previously hashed types], use the letter
// 'R' as the marker
addULEB128('R');
addULEB128(Attribute);
// and use the unsigned LEB128 encoding of [the index of T in the
// list] as the attribute value;
addULEB128(DieNumber);
}
void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag,
const DIE &Entry) {
assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend "
"tags. Add support here when there's "
"a use case");
// Step 5
// If the tag in Step 3 is one of [the below tags]
if ((Tag == dwarf::DW_TAG_pointer_type ||
Tag == dwarf::DW_TAG_reference_type ||
Tag == dwarf::DW_TAG_rvalue_reference_type ||
Tag == dwarf::DW_TAG_ptr_to_member_type) &&
// and the referenced type (via the [below attributes])
// FIXME: This seems overly restrictive, and causes hash mismatches
// there's a decl/def difference in the containing type of a
// ptr_to_member_type, but it's what DWARF says, for some reason.
Attribute == dwarf::DW_AT_type) {
// ... has a DW_AT_name attribute,
StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name);
if (!Name.empty()) {
hashShallowTypeReference(Attribute, Entry, Name);
return;
}
}
unsigned &DieNumber = Numbering[&Entry];
if (DieNumber) {
hashRepeatedTypeReference(Attribute, DieNumber);
return;
}
// otherwise, b) use the letter 'T' as the marker, ...
addULEB128('T');
addULEB128(Attribute);
// ... process the type T recursively by performing Steps 2 through 7, and
// use the result as the attribute value.
DieNumber = Numbering.size();
computeHash(Entry);
}
// Hash all of the values in a block like set of values. This assumes that
// all of the data is going to be added as integers.
void DIEHash::hashBlockData(const DIE::const_value_range &Values) {
for (const auto &V : Values)
Hash.update((uint64_t)V.getDIEInteger().getValue());
}
// Hash the contents of a loclistptr class.
void DIEHash::hashLocList(const DIELocList &LocList) {
HashingByteStreamer Streamer(*this);
DwarfDebug &DD = *AP->getDwarfDebug();
const DebugLocStream &Locs = DD.getDebugLocs();
for (const auto &Entry : Locs.getEntries(Locs.getList(LocList.getValue())))
DD.emitDebugLocEntry(Streamer, Entry);
}
// Hash an individual attribute \param Attr based on the type of attribute and
// the form.
void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {
dwarf::Attribute Attribute = Value.getAttribute();
// Other attribute values use the letter 'A' as the marker, and the value
// consists of the form code (encoded as an unsigned LEB128 value) followed by
// the encoding of the value according to the form code. To ensure
// reproducibility of the signature, the set of forms used in the signature
// computation is limited to the following: DW_FORM_sdata, DW_FORM_flag,
// DW_FORM_string, and DW_FORM_block.
switch (Value.getType()) {
case DIEValue::isNone:
llvm_unreachable("Expected valid DIEValue");
// 7.27 Step 3
// ... An attribute that refers to another type entry T is processed as
// follows:
case DIEValue::isEntry:
hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry());
break;
case DIEValue::isInteger: {
addULEB128('A');
addULEB128(Attribute);
switch (Value.getForm()) {
case dwarf::DW_FORM_data1:
case dwarf::DW_FORM_data2:
case dwarf::DW_FORM_data4:
case dwarf::DW_FORM_data8:
case dwarf::DW_FORM_udata:
case dwarf::DW_FORM_sdata:
addULEB128(dwarf::DW_FORM_sdata);
addSLEB128((int64_t)Value.getDIEInteger().getValue());
break;
// DW_FORM_flag_present is just flag with a value of one. We still give it a
// value so just use the value.
case dwarf::DW_FORM_flag_present:
case dwarf::DW_FORM_flag:
addULEB128(dwarf::DW_FORM_flag);
addULEB128((int64_t)Value.getDIEInteger().getValue());
break;
default:
llvm_unreachable("Unknown integer form!");
}
break;
}
case DIEValue::isString:
addULEB128('A');
addULEB128(Attribute);
addULEB128(dwarf::DW_FORM_string);
addString(Value.getDIEString().getString());
break;
case DIEValue::isInlineString:
addULEB128('A');
addULEB128(Attribute);
addULEB128(dwarf::DW_FORM_string);
addString(Value.getDIEInlineString().getString());
break;
case DIEValue::isBlock:
case DIEValue::isLoc:
case DIEValue::isLocList:
addULEB128('A');
addULEB128(Attribute);
addULEB128(dwarf::DW_FORM_block);
if (Value.getType() == DIEValue::isBlock) {
addULEB128(Value.getDIEBlock().ComputeSize(AP));
hashBlockData(Value.getDIEBlock().values());
} else if (Value.getType() == DIEValue::isLoc) {
addULEB128(Value.getDIELoc().ComputeSize(AP));
hashBlockData(Value.getDIELoc().values());
} else {
// We could add the block length, but that would take
// a bit of work and not add a lot of uniqueness
// to the hash in some way we could test.
hashLocList(Value.getDIELocList());
}
break;
// FIXME: It's uncertain whether or not we should handle this at the moment.
case DIEValue::isExpr:
case DIEValue::isLabel:
case DIEValue::isDelta:
llvm_unreachable("Add support for additional value types.");
}
}
// Go through the attributes from \param Attrs in the order specified in 7.27.4
// and hash them.
void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) {
#define HANDLE_DIE_HASH_ATTR(NAME) \
{ \
if (Attrs.NAME) \
hashAttribute(Attrs.NAME, Tag); \
}
#include "DIEHashAttributes.def"
// FIXME: Add the extended attributes.
}
// Add all of the attributes for \param Die to the hash.
void DIEHash::addAttributes(const DIE &Die) {
DIEAttrs Attrs = {};
collectAttributes(Die, Attrs);
hashAttributes(Attrs, Die.getTag());
}
void DIEHash::hashNestedType(const DIE &Die, StringRef Name) {
// 7.27 Step 7
// ... append the letter 'S',
addULEB128('S');
// the tag of C,
addULEB128(Die.getTag());
// and the name.
addString(Name);
}
// Compute the hash of a DIE. This is based on the type signature computation
// given in section 7.27 of the DWARF4 standard. It is the md5 hash of a
// flattened description of the DIE.
void DIEHash::computeHash(const DIE &Die) {
// Append the letter 'D', followed by the DWARF tag of the DIE.
addULEB128('D');
addULEB128(Die.getTag());
// Add each of the attributes of the DIE.
addAttributes(Die);
// Then hash each of the children of the DIE.
for (auto &C : Die.children()) {
// 7.27 Step 7
// If C is a nested type entry or a member function entry, ...
if (isType(C.getTag()) || C.getTag() == dwarf::DW_TAG_subprogram) {
StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);
// ... and has a DW_AT_name attribute
if (!Name.empty()) {
hashNestedType(C, Name);
continue;
}
}
computeHash(C);
}
// Following the last (or if there are no children), append a zero byte.
Hash.update(makeArrayRef((uint8_t)'\0'));
}
/// This is based on the type signature computation given in section 7.27 of the
/// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
/// with the inclusion of the full CU and all top level CU entities.
// TODO: Initialize the type chain at 0 instead of 1 for CU signatures.
uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) {
Numbering.clear();
Numbering[&Die] = 1;
if (!DWOName.empty())
Hash.update(DWOName);
// Hash the DIE.
computeHash(Die);
// Now return the result.
MD5::MD5Result Result;
Hash.final(Result);
// ... take the least significant 8 bytes and return those. Our MD5
// implementation always returns its results in little endian, so we actually
// need the "high" word.
return Result.high();
}
/// This is based on the type signature computation given in section 7.27 of the
/// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
/// with the inclusion of additional forms not specifically called out in the
/// standard.
uint64_t DIEHash::computeTypeSignature(const DIE &Die) {
Numbering.clear();
Numbering[&Die] = 1;
if (const DIE *Parent = Die.getParent())
addParentContext(*Parent);
// Hash the DIE.
computeHash(Die);
// Now return the result.
MD5::MD5Result Result;
Hash.final(Result);
// ... take the least significant 8 bytes and return those. Our MD5
// implementation always returns its results in little endian, so we actually
// need the "high" word.
return Result.high();
}
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