Files
clang-p2996/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.h
Pavel Labath 7cfa74fc69 [lldb/DWARF] Trust CU DW_AT_low/high_pc information when building address tables
Summary:
The code in DWARFCompileUnit::BuildAddressRangeTable tries hard to avoid
relying on DW_AT_low/high_pc for compile unit range information, and
this logic is a big cause of llvm/lldb divergence in the lowest layers
of dwarf parsing code.

The implicit assumption in that code is that this information (as opposed to
DW_AT_ranges) is unreliable. However, I have not been able to verify
that assumption. It is definitely not true for all present-day
compilers (gcc, clang, icc), and it was also not the case for the
historic compilers that I have been able to get a hold of (thanks Matt
Godbolt).

All compiler included in my research either produced correct
DW_AT_ranges or .debug_aranges entries, or they produced no DW_AT_hi/lo
pc at all. The detailed findings are:
- gcc >= 4.4: produces DW_AT_ranges and .debug_aranges
- 4.1 <= gcc < 4.4: no DW_AT_ranges, no DW_AT_high_pc, .debug_aranges
  present. The upper version range here is uncertain as godbolt.org does
  not have intermediate versions.
- gcc < 4.1: no versions on godbolt.org
- clang >= 3.5: produces DW_AT_ranges, and (optionally) .debug_aranges
- 3.4 <= clang < 3.5: no DW_AT_ranges, no DW_AT_high_pc, .debug_aranges
  present.
- clang <= 3.3: no DW_AT_ranges, no DW_AT_high_pc, no .debug_aranges
- icc >= 16.0.1: produces DW_AT_ranges
- icc < 16.0.1: no functional versions on godbolt.org (some are present
  but fail to compile)

Based on this analysis, I believe it is safe to start trusting
DW_AT_low/high_pc information in dwarf as well as remove the code for
manually reconstructing range information by traversing the DIE
structure, and just keep the line table fallback. The only compilers
where this will change behavior are pre-3.4 clangs, which are almost 7
years old now. However, the functionality should remain unchanged
because we will be able to reconstruct this information from the line
table, which seems to be needed for some line-tables-only scenarios
anyway (haven't researched this too much, but at least some compilers
seem to emit DW_AT_ranges even in these situations).

In addition, benchmarks showed that for these compilers computing the
ranges via line tables is noticably faster than doing so via the DIE
tree.

Other advantages include simplifying the code base, removing some
untested code (the only test changes are recent tests with overly
reduced synthetic dwarf), and increasing llvm convergence.

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D78489
2020-04-23 16:12:41 +02:00

191 lines
7.4 KiB
C++

//===-- DWARFDebugInfoEntry.h -----------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
#ifndef LLDB_SOURCE_PLUGINS_SYMBOLFILE_DWARF_DWARFDEBUGINFOENTRY_H
#define LLDB_SOURCE_PLUGINS_SYMBOLFILE_DWARF_DWARFDEBUGINFOENTRY_H
#include "SymbolFileDWARF.h"
#include "llvm/ADT/SmallVector.h"
#include "DWARFAbbreviationDeclaration.h"
#include "DWARFDebugAbbrev.h"
#include "DWARFDebugRanges.h"
#include <map>
#include <set>
#include <vector>
class DWARFDeclContext;
#define DIE_SIBLING_IDX_BITSIZE 31
/// DWARFDebugInfoEntry objects assume that they are living in one big
/// vector and do pointer arithmetic on their this pointers. Don't
/// pass them by value. Due to the way they are constructed in a
/// std::vector, we cannot delete the copy constructor.
class DWARFDebugInfoEntry {
public:
typedef std::vector<DWARFDebugInfoEntry> collection;
typedef collection::iterator iterator;
typedef collection::const_iterator const_iterator;
DWARFDebugInfoEntry()
: m_offset(DW_INVALID_OFFSET), m_parent_idx(0), m_sibling_idx(0),
m_has_children(false), m_abbr_idx(0), m_tag(llvm::dwarf::DW_TAG_null) {}
explicit operator bool() const { return m_offset != DW_INVALID_OFFSET; }
bool operator==(const DWARFDebugInfoEntry &rhs) const;
bool operator!=(const DWARFDebugInfoEntry &rhs) const;
void BuildFunctionAddressRangeTable(const DWARFUnit *cu,
DWARFDebugAranges *debug_aranges) const;
bool Extract(const lldb_private::DWARFDataExtractor &data,
const DWARFUnit *cu, lldb::offset_t *offset_ptr);
size_t GetAttributes(const DWARFUnit *cu,
DWARFAttributes &attrs,
uint32_t curr_depth = 0)
const; // "curr_depth" for internal use only, don't set this yourself!!!
dw_offset_t
GetAttributeValue(const DWARFUnit *cu, const dw_attr_t attr,
DWARFFormValue &formValue,
dw_offset_t *end_attr_offset_ptr = nullptr,
bool check_specification_or_abstract_origin = false) const;
const char *GetAttributeValueAsString(
const DWARFUnit *cu, const dw_attr_t attr, const char *fail_value,
bool check_specification_or_abstract_origin = false) const;
uint64_t GetAttributeValueAsUnsigned(
const DWARFUnit *cu, const dw_attr_t attr, uint64_t fail_value,
bool check_specification_or_abstract_origin = false) const;
DWARFDIE GetAttributeValueAsReference(
const DWARFUnit *cu, const dw_attr_t attr,
bool check_specification_or_abstract_origin = false) const;
uint64_t GetAttributeValueAsAddress(
const DWARFUnit *cu, const dw_attr_t attr, uint64_t fail_value,
bool check_specification_or_abstract_origin = false) const;
dw_addr_t
GetAttributeHighPC(const DWARFUnit *cu, dw_addr_t lo_pc, uint64_t fail_value,
bool check_specification_or_abstract_origin = false) const;
bool GetAttributeAddressRange(
const DWARFUnit *cu, dw_addr_t &lo_pc, dw_addr_t &hi_pc,
uint64_t fail_value,
bool check_specification_or_abstract_origin = false) const;
size_t GetAttributeAddressRanges(
DWARFUnit *cu, DWARFRangeList &ranges, bool check_hi_lo_pc,
bool check_specification_or_abstract_origin = false) const;
const char *GetName(const DWARFUnit *cu) const;
const char *GetMangledName(const DWARFUnit *cu,
bool substitute_name_allowed = true) const;
const char *GetPubname(const DWARFUnit *cu) const;
const char *GetQualifiedName(DWARFUnit *cu, std::string &storage) const;
const char *GetQualifiedName(DWARFUnit *cu, const DWARFAttributes &attributes,
std::string &storage) const;
void Dump(const DWARFUnit *cu, lldb_private::Stream &s,
uint32_t recurse_depth) const;
static void
DumpAttribute(const DWARFUnit *cu,
const lldb_private::DWARFDataExtractor &data,
lldb::offset_t *offset_ptr, lldb_private::Stream &s,
dw_attr_t attr, DWARFFormValue &form_value);
bool GetDIENamesAndRanges(
DWARFUnit *cu, const char *&name, const char *&mangled,
DWARFRangeList &rangeList, int &decl_file, int &decl_line,
int &decl_column, int &call_file, int &call_line, int &call_column,
lldb_private::DWARFExpression *frame_base = nullptr) const;
const DWARFAbbreviationDeclaration *
GetAbbreviationDeclarationPtr(const DWARFUnit *cu) const;
lldb::offset_t GetFirstAttributeOffset() const;
dw_tag_t Tag() const { return m_tag; }
bool IsNULL() const { return m_abbr_idx == 0; }
dw_offset_t GetOffset() const { return m_offset; }
bool HasChildren() const { return m_has_children; }
void SetHasChildren(bool b) { m_has_children = b; }
// We know we are kept in a vector of contiguous entries, so we know
// our parent will be some index behind "this".
DWARFDebugInfoEntry *GetParent() {
return m_parent_idx > 0 ? this - m_parent_idx : nullptr;
}
const DWARFDebugInfoEntry *GetParent() const {
return m_parent_idx > 0 ? this - m_parent_idx : nullptr;
}
// We know we are kept in a vector of contiguous entries, so we know
// our sibling will be some index after "this".
DWARFDebugInfoEntry *GetSibling() {
return m_sibling_idx > 0 ? this + m_sibling_idx : nullptr;
}
const DWARFDebugInfoEntry *GetSibling() const {
return m_sibling_idx > 0 ? this + m_sibling_idx : nullptr;
}
// We know we are kept in a vector of contiguous entries, so we know
// we don't need to store our child pointer, if we have a child it will
// be the next entry in the list...
DWARFDebugInfoEntry *GetFirstChild() {
return HasChildren() ? this + 1 : nullptr;
}
const DWARFDebugInfoEntry *GetFirstChild() const {
return HasChildren() ? this + 1 : nullptr;
}
DWARFDeclContext GetDWARFDeclContext(DWARFUnit *cu) const;
DWARFDIE GetParentDeclContextDIE(DWARFUnit *cu) const;
DWARFDIE GetParentDeclContextDIE(DWARFUnit *cu,
const DWARFAttributes &attributes) const;
void SetSiblingIndex(uint32_t idx) { m_sibling_idx = idx; }
void SetParentIndex(uint32_t idx) { m_parent_idx = idx; }
// This function returns true if the variable scope is either
// global or (file-static). It will return false for static variables
// that are local to a function, as they have local scope.
bool IsGlobalOrStaticScopeVariable() const;
protected:
static DWARFDeclContext
GetDWARFDeclContextStatic(const DWARFDebugInfoEntry *die, DWARFUnit *cu);
dw_offset_t m_offset; // Offset within the .debug_info/.debug_types
uint32_t m_parent_idx; // How many to subtract from "this" to get the parent.
// If zero this die has no parent
uint32_t m_sibling_idx : 31, // How many to add to "this" to get the sibling.
// If it is zero, then the DIE doesn't have children, or the
// DWARF claimed it had children but the DIE only contained
// a single NULL terminating child.
m_has_children : 1;
uint16_t m_abbr_idx;
/// A copy of the DW_TAG value so we don't have to go through the compile
/// unit abbrev table
dw_tag_t m_tag = llvm::dwarf::DW_TAG_null;
};
#endif // LLDB_SOURCE_PLUGINS_SYMBOLFILE_DWARF_DWARFDEBUGINFOENTRY_H