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MC: Support quoted symbol names #138817

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Merged
MaskRay merged 3 commits into from
May 8, 2025
Merged

MC: Support quoted symbol names #138817

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1eaf8a5
[𝘀𝗽𝗿] initial version
MaskRay May 7, 2025
5bcfefe
improve test
MaskRay May 8, 2025
688b667
update safeseh.s
MaskRay May 8, 2025
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21 changes: 21 additions & 0 deletions llvm/lib/MC/MCContext.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -212,6 +212,27 @@ MCDataFragment *MCContext::allocInitialFragment(MCSection &Sec) {
MCSymbol *MCContext::getOrCreateSymbol(const Twine &Name) {
SmallString<128> NameSV;
StringRef NameRef = Name.toStringRef(NameSV);
if (NameRef.contains('\\')) {
NameSV = NameRef;
size_t S = 0;
// Support escaped \\ and \" as in GNU Assembler. GAS issues a warning for
// other characters following \\, which we do not implement due to code
// structure.
for (size_t I = 0, E = NameSV.size(); I < E; ++I) {
char C = NameSV[I];
if (C == '\\') {
switch (NameSV[I + 1]) {
case '"':
case '\\':
C = NameSV[++I];
break;
}
}
NameSV[S++] = C;
}
NameSV.resize(S);
NameRef = NameSV;
}
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@nikic nikic Aug 31, 2025

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Shouldn't this unescaping only be done when parsing textual assembly in AsmParser, but not when programmatically creating symbols?

I'd expect the LLVM IR @"\\\22" = constant i8 0 to result in "\\\"": rather than "\"":, as it does with this patch. (Previously it resulted in "\\"":, which is also wrong, but at least only affects the case where you're emitting assembly.)

See rust-lang/rust#146065 for a regression from this change. Of course we could easily apply additional escaping on the Rust side, but I think the current behavior here isn't right.

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@MaskRay MaskRay Sep 8, 2025

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Sorry, just saw this message. I agree that ideally this should be limited to texual assembly in MC/MCParser/AsmParser.cpp. Unfortunately this is challenging because the wide-used API AsmParser::parseIdentifier (used ~107 times) takes a StringRef instead of an owned string. It seems a lot of work to fix parseIdentifier...

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@nikic nikic Sep 11, 2025

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Yes, this is a problem. I put up #158106 to put at least some of these uses behind a common API.

A simple option would be to just keep StringRef and have the backing storage in an Allocator. This would avoid API changes and should not really be a performance or memory usage problem as long as quoted symbols are rare.

Though I'm not sure whether all uses of parseIdentifier should parse quoted strings or not.


assert(!NameRef.empty() && "Normal symbols cannot be unnamed!");

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2 changes: 2 additions & 0 deletions llvm/lib/MC/MCSymbol.cpp
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Expand Up @@ -74,6 +74,8 @@ void MCSymbol::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
OS << "\\n";
else if (C == '"')
OS << "\\\"";
else if (C == '\\')
OS << "\\\\";
else
OS << C;
}
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3 changes: 3 additions & 0 deletions llvm/test/MC/AsmParser/quoted.s
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Expand Up @@ -9,6 +9,9 @@
"a b":
call "a b"

# CHECK: "a b\\":
"a b\\":

#--- err.s
"a\":
# ERR: 1:2: error: unterminated string constant
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4 changes: 2 additions & 2 deletions llvm/test/MC/COFF/safeseh.s
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Expand Up @@ -2,5 +2,5 @@

// check that we quote the output of .safeseh

.safeseh "\01foo"
// CHECK: .safeseh "\01foo"
.safeseh "\\foo"
// CHECK: .safeseh "\\foo"
22 changes: 19 additions & 3 deletions llvm/test/MC/ELF/symbol-names.s
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@@ -1,12 +1,28 @@
// RUN: llvm-mc -triple i686-pc-linux -filetype=obj %s -o - | llvm-readobj --symbols - | FileCheck %s
// RUN: llvm-mc -triple=x86_64 -filetype=obj %s | llvm-objdump -tdr - | FileCheck %s

// MC allows ?'s in symbol names as an extension.

// CHECK-LABEL:SYMBOL TABLE:
// CHECK-NEXT: 0000000000000001 l F .text 0000000000000000 a"b\{{$}}
// CHECK-NEXT: 0000000000000006 l .text 0000000000000000 a\{{$}}
// CHECK-NEXT: 0000000000000000 g F .text 0000000000000000 foo?bar
// CHECK-NEXT: 0000000000000000 *UND* 0000000000000000 a"b\q{{$}}
// CHECK-EMPTY:

.text
.globl foo?bar
.type foo?bar, @function
foo?bar:
ret

// CHECK: Symbol
// CHECK: Name: foo?bar
// CHECK-LABEL:<a"b\>:
// CHECK-NEXT: callq {{.*}} <a"b\>
// CHECK-LABEL:<a\>:
// CHECK-NEXT: callq {{.*}}
// CHECK-NEXT: R_X86_64_PLT32 a"b\q-0x4
.type "a\"b\\", @function
"a\"b\\":
call "a\"b\\"
"a\\":
/// GAS emits a warning for \q
call "a\"b\q"
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