Don't attempt to unload cdac

[rcj1]

As cDAC is a NativeAOT library, it cannot be safely unloaded. #131960 should prevent an actual unmapping from happening, but this makes the intent clear.

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Pull request overview

This PR clarifies that the cDAC (a NativeAOT library) should not be unloaded on Unix by guarding FreeLibrary calls with #ifndef HOST_UNIX, aligning intent with the prior change to prevent actual unmapping.

Changes:

• Skip unloading the cDAC library on Unix when initialization fails.
• Skip unloading the cDAC library on Unix during CDAC destruction.

Show a summary per file

File	Description
src/coreclr/debug/daccess/cdac.cpp	Adds HOST_UNIX guards around FreeLibrary calls to avoid attempting to unload cDAC on Unix.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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Review details

Suppressed comments (2)

src/coreclr/debug/daccess/cdac.cpp:172

• On Unix the module is now intentionally kept loaded by skipping FreeLibrary. Without an explanatory comment, this looks like a resource leak and makes the lifetime rule easy to misunderstand. Consider adding a short #else comment clarifying why unloading is avoided here.

#ifndef HOST_UNIX
        ::FreeLibrary(m_module);
#endif // HOST_UNIX

src/coreclr/debug/daccess/cdac.cpp:141

• On Unix this now intentionally skips freeing the cDAC module, which can look like an accidental leak/refcount imbalance to future maintainers. Add an explicit comment in the #else branch explaining that this is deliberate (NativeAOT library unload is unsafe) so the behavior isn’t “fixed” later.

This issue also appears on line 170 of the same file.

#ifndef HOST_UNIX
        ::FreeLibrary(cdacLib);
#endif // HOST_UNIX

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

src/coreclr/debug/daccess/cdac.cpp:140

• Since FreeLibrary was removed, a failed cdac_reader_init (or any subsequent CDAC::Create call) leaves the newly loaded module referenced forever. If DAC instances are created repeatedly in a long-lived process, this can accumulate module references unnecessarily. Consider caching the loaded HMODULE and reusing it for subsequent Create calls so the library is loaded once per process while still never being unloaded.

    intptr_t handle;
    if (init(descriptorAddr, &ReadFromTargetCallback, &WriteToTargetCallback, &ReadThreadContext, &WriteThreadContext, allocCallback, target, &handle) != 0)
    {
        return {};
    }

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Lite