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Merged
JDevlieghere merged 15 commits into from
Jul 12, 2025
Merged

[lldb] Add DWARFExpressionEntry and GetExpressionEntryAtAddress() to … #144238

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8ed8c54
[lldb] Add DWARFExpressionEntry and GetExpressionEntryAtAddress() to …
UltimateForce21 Jun 11, 2025
1db5002
Update lldb/include/lldb/Expression/DWARFExpressionList.h
UltimateForce21 Jun 19, 2025
a26010b
Update lldb/include/lldb/Expression/DWARFExpressionList.h
UltimateForce21 Jun 19, 2025
72237b7
Update lldb/source/Expression/DWARFExpressionList.cpp
UltimateForce21 Jun 19, 2025
94e4951
Update DWARFExpressionList.h
UltimateForce21 Jun 24, 2025
e8142da
Update DWARFExpressionList.cpp
UltimateForce21 Jun 24, 2025
7e8741e
Update DWARFExpressionList.h
UltimateForce21 Jun 28, 2025
c4cd77f
Update DWARFExpressionList.cpp
UltimateForce21 Jun 28, 2025
62c02a9
Change GetExpressionEntryAtAddress to return std::optional instead of…
UltimateForce21 Jun 29, 2025
d015971
Update DWARFExpressionList.cpp
UltimateForce21 Jul 2, 2025
60898ea
Add underflow/overflow checks to GetExpressionEntryAtAddressi
UltimateForce21 Jul 3, 2025
3462165
Make file_range optional in DWARFExpressionEntry for always-valid expr
UltimateForce21 Jul 8, 2025
c01a747
Merge branch 'main' into add-dwarfexprentry-api
UltimateForce21 Jul 9, 2025
ec3ac93
Merge branch 'main' into add-dwarfexprentry-api
UltimateForce21 Jul 10, 2025
38baa90
Fixed formating issues
UltimateForce21 Jul 10, 2025
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15 changes: 15 additions & 0 deletions lldb/include/lldb/Expression/DWARFExpressionList.h
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
#ifndef LLDB_EXPRESSION_DWARFEXPRESSIONLIST_H
#define LLDB_EXPRESSION_DWARFEXPRESSIONLIST_H

#include "lldb/Core/AddressRange.h"
#include "lldb/Core/Value.h"
#include "lldb/Expression/DWARFExpression.h"
#include "lldb/Utility/RangeMap.h"
Expand Down Expand Up @@ -58,6 +59,20 @@ class DWARFExpressionList {
}

lldb::addr_t GetFuncFileAddress() { return m_func_file_addr; }

/// Represents an entry in the DWARFExpressionList with all needed metadata.
struct DWARFExpressionEntry {
/// Represents a DWARF location range in the DWARF unit’s file‐address space
AddressRange file_range;
const DWARFExpression *expr;
};

/// Returns a DWARFExpressionEntry whose file_range contains the given
/// load‐address. `func_load_addr` is the load‐address of the function
/// start; `load_addr` is the full runtime PC. On success, `expr` is non-null.
std::optional<DWARFExpressionEntry>
GetExpressionEntryAtAddress(lldb::addr_t func_load_addr,
lldb::addr_t load_addr) const;

const DWARFExpression *GetExpressionAtAddress(lldb::addr_t func_load_addr,
lldb::addr_t load_addr) const;
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25 changes: 25 additions & 0 deletions lldb/source/Expression/DWARFExpressionList.cpp
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Expand Up @@ -6,6 +6,7 @@
//
//===----------------------------------------------------------------------===//

#include "lldb/Core/AddressRange.h"
#include "lldb/Expression/DWARFExpressionList.h"
#include "lldb/Symbol/Function.h"
#include "lldb/Target/RegisterContext.h"
Expand Down Expand Up @@ -53,6 +54,30 @@ bool DWARFExpressionList::ContainsAddress(lldb::addr_t func_load_addr,
return GetExpressionAtAddress(func_load_addr, addr) != nullptr;
}

std::optional<DWARFExpressionList::DWARFExpressionEntry>
DWARFExpressionList::GetExpressionEntryAtAddress(lldb::addr_t func_load_addr,
lldb::addr_t load_addr) const {
if (const DWARFExpression *always = GetAlwaysValidExpr()) {
AddressRange full_range(m_func_file_addr, /*size=*/LLDB_INVALID_ADDRESS);
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@JDevlieghere JDevlieghere Jul 7, 2025

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The name of the argument is byte_size so let's match that.

Suggested change
AddressRange full_range(m_func_file_addr, /*size=*/LLDB_INVALID_ADDRESS);
AddressRange full_range(m_func_file_addr, /*byte_size=*/LLDB_INVALID_ADDRESS);

I'm somewhat skeptical of LLDB_INVALID_ADDRESS as the size. Is there precedent for using that to indicate we don't know the size? I'm worried about whether the existing code is resilient to that. Would it make sense to make the AddressRange optional in the struct for the always-valid-single-expression case?

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@UltimateForce21 UltimateForce21 Jul 8, 2025

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I believe using an optional AddressRange the way you said is a safer option and probably more clear for users, I have committed the change.

return DWARFExpressionEntry{full_range, always};
}

if (func_load_addr == LLDB_INVALID_ADDRESS)
func_load_addr = m_func_file_addr;

// translate to file-relative PC
lldb::addr_t file_pc = load_addr - func_load_addr + m_func_file_addr;
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@adrian-prantl adrian-prantl Jun 30, 2025

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You should be using subOverflow (https://llvm.org/doxygen/MathExtras_8h.html) here to guard against wrap-around.

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@UltimateForce21 UltimateForce21 Jul 3, 2025

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I dug into MathExtras and found that its AddOverflow and SubOverflow helpers are only defined for signed types. I they rely on two’s-complement signed overflow semantics and return the truncated signed result. Since lldb::addr_t is an unsigned address, I think using those helpers would either fail to compile or silently convert to signed semantics. So I tried to implement the signed overflow check into the function. Please let me know if you think it is alright.


if (const auto *entry = m_exprs.FindEntryThatContains(file_pc)) {
AddressRange range_in_file(entry->GetRangeBase(),
entry->GetRangeEnd() - entry->GetRangeBase());
return DWARFExpressionEntry{range_in_file, &entry->data};
}

// No entry covers this PC:
return std::nullopt;
}

const DWARFExpression *
DWARFExpressionList::GetExpressionAtAddress(lldb::addr_t func_load_addr,
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@adrian-prantl adrian-prantl Jun 16, 2025

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Out of curiosity: Do we still need this API, or is it just a subset of the function above?

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@UltimateForce21 UltimateForce21 Jun 19, 2025

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As you know the new function GetExpressionEntryAtAddress, does almost exact same thing as this one. I don't see this function being used anywhere else in the lldb code base, so maybe it can be removed, but to be safe I did not want to alter it. But from what I can tell, it should be okay to remove it. We can also choose to keep it and maybe refactor it to just call the GetExpressionEntryAtAddress and just return the DWARFExpression *expr.

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@adrian-prantl adrian-prantl Jun 21, 2025

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If it's completely unused, and there is no indication that was added in support of any downstream clients (either as a comment or in the commit message) we could consider deleting it in a separate PR. Not urgent.

lldb::addr_t load_addr) const {
Expand Down