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[lldb] Log errors to the system log if they would otherwise get dropped #111911

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Merged
merged 4 commits into from
Oct 22, 2024
Merged

[lldb] Log errors to the system log if they would otherwise get dropped #111911

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[lldb] Log errors to the system log if they would otherwise get dropped
JDevlieghere Oct 10, 2024
99b70b3
Address Pavel's feedback
JDevlieghere Oct 13, 2024
28174fa
Store instead of exchange
JDevlieghere Oct 13, 2024
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JDevlieghere Oct 15, 2024
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15 changes: 15 additions & 0 deletions lldb/include/lldb/Utility/Log.h
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Original file line number Diff line number Diff line change
Expand Up @@ -335,6 +335,15 @@ template <typename Cat> Log *GetLog(Cat mask) {
return LogChannelFor<Cat>().GetLog(Log::MaskType(mask));
}

/// Getter and setter for the error log (see g_error_log).
/// The error log is set to the system log in SystemInitializerFull. We can't
/// use the system log directly because that would violate the layering between
/// Utility and Host.
/// @{
void SetLLDBErrorLog(Log *log);
Log *GetLLDBErrorLog();
/// @}

} // namespace lldb_private

/// The LLDB_LOG* macros defined below are the way to emit log messages.
Expand Down Expand Up @@ -387,6 +396,9 @@ template <typename Cat> Log *GetLog(Cat mask) {
if (log_private && error_private) { \
log_private->FormatError(::std::move(error_private), __FILE__, __func__, \
__VA_ARGS__); \
} else if (::lldb_private::Log *log_error = GetLLDBErrorLog()) { \
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@labath labath Oct 11, 2024

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I'd recommend structuring this in a way that avoids evaluating __VA_ARGS__ more than once. You could e.g. insert a if(!log_private) log_private = GetLLDBErrorLog() statement before this if.

(I know that the macro gets dynamically evaluated only once, but I was recently reading about how this innocent-looking macro in the linux kernel exploded to several dozen kilobytes of goo. We're not there yet, but this should help anyone looking at the preprocessed output, and also help the compiler generate less code)

log_error->FormatError(::std::move(error_private), __FILE__, __func__, \
__VA_ARGS__); \
} else \
::llvm::consumeError(::std::move(error_private)); \
} while (0)
Expand All @@ -401,6 +413,9 @@ template <typename Cat> Log *GetLog(Cat mask) {
if (log_private && log_private->GetVerbose() && error_private) { \
log_private->FormatError(::std::move(error_private), __FILE__, __func__, \
__VA_ARGS__); \
} else if (::lldb_private::Log *log_error = GetLLDBErrorLog()) { \
log_error->FormatError(::std::move(error_private), __FILE__, __func__, \
__VA_ARGS__); \
} else \
::llvm::consumeError(::std::move(error_private)); \
} while (0)
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3 changes: 3 additions & 0 deletions lldb/source/API/SystemInitializerFull.cpp
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Expand Up @@ -84,6 +84,9 @@ llvm::Error SystemInitializerFull::Initialize() {
// Use the Debugger's LLDBAssert callback.
SetLLDBAssertCallback(Debugger::AssertCallback);

// Use the system log to report errors that would otherwise get dropped.
SetLLDBErrorLog(GetLog(SystemLog::System));

LLDB_LOG(GetLog(SystemLog::System), "{0}", GetVersion());

return llvm::Error::success();
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8 changes: 8 additions & 0 deletions lldb/source/Utility/Log.cpp
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Expand Up @@ -43,6 +43,10 @@ char TeeLogHandler::ID;

llvm::ManagedStatic<Log::ChannelMap> Log::g_channel_map;

// The error log is used by LLDB_LOG_ERROR and LLDB_LOG_ERRORV. If the given
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@labath labath Oct 14, 2024

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Suggested change
// The error log is used by LLDB_LOG_ERROR and LLDB_LOG_ERRORV. If the given
// The error log is used by LLDB_LOG_ERROR. If the given

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@JDevlieghere JDevlieghere Oct 22, 2024

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Already fixed in the latest version of this PR :-)

// log channel is not enabled, error messages are logged to the error log.
static std::atomic<Log *> g_error_log = nullptr;

void Log::ForEachCategory(
const Log::ChannelMap::value_type &entry,
llvm::function_ref<void(llvm::StringRef, llvm::StringRef)> lambda) {
Expand Down Expand Up @@ -460,3 +464,7 @@ void TeeLogHandler::Emit(llvm::StringRef message) {
m_first_log_handler->Emit(message);
m_second_log_handler->Emit(message);
}

void lldb_private::SetLLDBErrorLog(Log *log) { g_error_log.exchange(log); }

Log *lldb_private::GetLLDBErrorLog() { return g_error_log; }
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