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[BOLT] Check if symbol is in data area of function #160143

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[BOLT] Check if symbol is in data area of function #160143

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36823a0
[BOLT] Check if symbol is in data area of function
Sep 22, 2025
797b5b2
Fix warning messgage and test comment
Sep 23, 2025
550efd1
Make getEntryIDForSymbol() return optional and address review comments
Oct 7, 2025
3e9e9c7
Expand test comment to 80 char
Oct 7, 2025
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3 changes: 2 additions & 1 deletion bolt/include/bolt/Core/BinaryFunction.h
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Original file line number Diff line number Diff line change
Expand Up @@ -650,7 +650,8 @@ class BinaryFunction {
///
/// Prefer to use BinaryContext::getFunctionForSymbol(EntrySymbol, &ID)
/// instead of calling this function directly.
uint64_t getEntryIDForSymbol(const MCSymbol *EntrySymbol) const;
std::optional<uint64_t>
getEntryIDForSymbol(const MCSymbol *EntrySymbol) const;

/// If the function represents a secondary split function fragment, set its
/// parent fragment to \p BF.
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11 changes: 9 additions & 2 deletions bolt/lib/Core/BinaryContext.cpp
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Expand Up @@ -2374,8 +2374,15 @@ BinaryFunction *BinaryContext::getFunctionForSymbol(const MCSymbol *Symbol,
return nullptr;

BinaryFunction *BF = BFI->second;
if (EntryDesc)
*EntryDesc = BF->getEntryIDForSymbol(Symbol);
if (EntryDesc) {
const uint64_t Address = BF->getAddress() + Symbol->getOffset();
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Hmm.. I'm not sure Symbol->getOffset() will always produce the expected output.

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Thanks for taking a look. Could you please elaborate on what might be the problem here?

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Ah yes, sorry. Symbol->getOffset() is not guaranteed to return the offset from the start of the function at arbitrary point of execution.

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As far as I understand, if Symbol->getOffset() does not return the symbol offset, then it returns 0. In which case const uint64_t Address = BF->getAddress() + Symbol->getOffset(); becomes the same as BF->getAddress(). For the purpose of this patch, I think that is fine. Whether we're checking the function address or the symbol address, the point is to check if we're in a data area (constant island) before proceeding. This check is only reached in getFunctionForSymbol as a way to prevent calling getEntryIDForSymbol, and avoid hitting the llvm_unreachable, if we're in a data area.

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I see. I'd prefer to make getEntryIDForSymbol() return an optional (i.e. remove the unreachable) and not rely on the implicit behavior.

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Okay, I'll look into making it an optional.

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Thanks!

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It's now returning an optional. I did keep the Symbol->getOffset() check in order to give a warning to the user, but we are no longer relying on it to avoid thellvm_unreachable.

if (BF->isInConstantIsland(Address)) {
this->outs() << "BOLT-WARNING: symbol " << Symbol->getName()
<< " is in data region of function " << BF->getOneName()
<< "(0x" << Twine::utohexstr(BF->getAddress()) << ").\n";
}
*EntryDesc = BF->getEntryIDForSymbol(Symbol).value_or(0);
}

return BF;
}
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6 changes: 3 additions & 3 deletions bolt/lib/Core/BinaryFunction.cpp
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Expand Up @@ -3855,7 +3855,8 @@ MCSymbol *BinaryFunction::getSymbolForEntryID(uint64_t EntryID) {
return nullptr;
}

uint64_t BinaryFunction::getEntryIDForSymbol(const MCSymbol *Symbol) const {
std::optional<uint64_t>
BinaryFunction::getEntryIDForSymbol(const MCSymbol *Symbol) const {
if (!isMultiEntry())
return 0;

Expand All @@ -3882,8 +3883,7 @@ uint64_t BinaryFunction::getEntryIDForSymbol(const MCSymbol *Symbol) const {
return NumEntries;
++NumEntries;
}

llvm_unreachable("symbol not found");
return std::nullopt;
}

bool BinaryFunction::forEachEntryPoint(EntryPointCallbackTy Callback) const {
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36 changes: 36 additions & 0 deletions bolt/test/AArch64/check-symbol-area.s
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@@ -0,0 +1,36 @@
// This test checks that when looking for a function corresponding to a
// symbol, BOLT is not looking through a data area (constant island).

# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q
# RUN: llvm-bolt %t.exe -o %t.bolt 2>&1 | FileCheck %s

// Before adding a check for constant islands, BOLT would exit with an error
// of the form: "symbol not found" and throw an LLVM UNREACHABLE error.
# CHECK-NOT: symbol not found
# CHECK-NOT: UNREACHABLE

// Now BOLT throws a warning and does not crash.
# CHECK: BOLT-WARNING: symbol third_block/1 is in data region of function first_block(0x{{[0-9a-f]+}}).

.text
.global main
main:
add x0, x1, x1
bl first_block
ret

.global first_block
$d:
first_block:
add x0, x1, x1
bl second_block
ret
second_block:
add x0, x1, x1
bl third_block
ret
$x:
third_block:
add x0, x1, x1
ret
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