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Warn on align directive with non-zero fill value in virtual sections #66792

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Merged
merged 1 commit into from
Sep 20, 2023
Merged

Warn on align directive with non-zero fill value in virtual sections #66792

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14 changes: 13 additions & 1 deletion llvm/lib/MC/MCParser/AsmParser.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3392,6 +3392,7 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, unsigned ValueSize) {
bool HasFillExpr = false;
int64_t FillExpr = 0;
int64_t MaxBytesToFill = 0;
SMLoc FillExprLoc;

auto parseAlign = [&]() -> bool {
if (parseAbsoluteExpression(Alignment))
Expand All @@ -3402,7 +3403,7 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, unsigned ValueSize) {
// .align 3,,4
if (getTok().isNot(AsmToken::Comma)) {
HasFillExpr = true;
if (parseAbsoluteExpression(FillExpr))
if (parseTokenLoc(FillExprLoc) || parseAbsoluteExpression(FillExpr))
return true;
}
if (parseOptionalToken(AsmToken::Comma))
Expand Down Expand Up @@ -3451,6 +3452,17 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, unsigned ValueSize) {
}
}

if (HasFillExpr) {
MCSection *Sec = getStreamer().getCurrentSectionOnly();
if (Sec && Sec->isVirtualSection()) {
ReturnVal |=
Warning(FillExprLoc, "ignoring non-zero fill value in " +
Sec->getVirtualSectionKind() + " section '" +
Sec->getName() + "'");
FillExpr = 0;
}
}

// Diagnose non-sensical max bytes to align.
if (MaxBytesLoc.isValid()) {
if (MaxBytesToFill < 1) {
Expand Down
3 changes: 3 additions & 0 deletions llvm/test/MC/ELF/nobits-non-zero-value.s
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Expand Up @@ -12,5 +12,8 @@
# CHECK: {{.*}}.s:[[#@LINE+1]]:3: error: SHT_NOBITS section '.bss' cannot have instructions
addb %al,(%rax)

# CHECK: {{.*}}.s:[[#@LINE+1]]:11: warning: ignoring non-zero fill value in SHT_NOBITS section '.bss'
.align 4, 42

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Add check lines for --no-warn / --fatal-warnings?

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Add check lines for --no-warn / --fatal-warnings?

Can you walk me through why we might want that, please? I'd have guessed that if we properly emit a warning and the diagnostic infrastructure is working as intended then we wouldn't need to test such interactions for all kinds of warnings.

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Warning() returns true (indicating an error) only in presense of --fatal-warnings. We might want to add the --fatal-warnings check to test that we didn't forget ReturnVal |= part. (However, it appears that omitting it does not change the behavior because top-level loop not only checks for the return value, but also for what hasPendingErrors() returns.)
Regarding --no-warn, I tend to agree with you.

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I added a RUN with --fatal-warnings. Let me know if it addresses your concerns properly.

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This check line would match if Warning was replaced with Error. I expected something like:

# RUN: not llvm-mc ... | FileCheck %s
# RUN: not llvm-mc --fatal-warnings ... | FileCheck --check-prefix=FATAL %s
...
# CHECK: ... warning: ignoring ...
# FATAL: ... error: ignoring...

I grepped mc tests and found only 4 tests that excercise --fatal-warnings, so I guess you can just drop the last commit and go ahead...

# CHECK: <unknown>:0: error: SHT_NOBITS section '.bss' cannot have non-zero initializers
.long 1