[lld] [LLD][COFF] Split native and EC .CRT chunks on ARM64X (PR #127203)

[Jacek Caban via llvm-commits]

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@@ -1156,6 +1162,11 @@ void Writer::createSections() {
     sec->addContributingPartialSection(pSec);
   }
 
+  if (ctx.hybridSymtab) {
+    if (OutputSection *sec = findSection(".CRT"))
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cjacek wrote:

> I guess we'd need to do something similar for every section that contains sorted ranges of pointers like this - presumably .ctors too?

Yes, that's #127205.

> What about sections like .tls? I presume that's coming up in a future patch too :-)

Surprisingly, no, `.tls` is a bit unusual. TLS callbacks are part of the `.CRT` section, so this PR already handles that.

The `.tls` section would seem like a good candidate for splitting, but based on my MSVC testing, it doesn’t behave that way. It’s somewhat similar to regular data handling, where EC data is mixed with native data. Since TLS callbacks are referenced by the TLS directory entry, I expected it to use ARM64X relocations in some way (for example, by defining `_tls_used` in both namespaces and swapping them in the directory entry using ARM64X relocs) but that doesn’t happen either.

With ARM64X, MSVC emits only the native directory. I guess that’s sufficient because the CRT later uses `.tls` and `.CRT` symbols without relying on `_tls_used` at runtime. That's already how LLD behaves, though I wouldn't rule out trying to improve it at some point...

https://github.com/llvm/llvm-project/pull/127203