[lld] [LLD][COFF] Add basic ARM64X dynamic relocations support (PR #118035)

[Martin Storsjö via llvm-commits]

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@@ -2660,6 +2693,18 @@ void Writer::checkLoadConfigGuardData(const T *loadConfig) {
     if (loadConfig->field != s->getVA())                                       \
       warn(#field " not set correctly in '_load_config_used'");
 
+  if (ctx.dynamicRelocs) {
+    IF_CONTAINS(DynamicValueRelocTableSection) {
+      loadConfig->DynamicValueRelocTableSection = relocSec->sectionIndex;
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mstorsjo wrote:

I see that you're merging the `checkLoadConfigGuardData` function into the caller, since you're reusing this context here, to not only _check_ member fields but also use the same `IF_CONTAINS()` to _set_ fields - is that a correct observation?

Are there other fields that we currently set in load config, which could benefit from `IF_CONTAINS()` in the same way? Such a refactoring, either moving the `IF_CONTAINS()` macro elsewhere, or merging `checkLoadConfigGuardData` into the caller to ease reusing these, feels like it's somewhat orthogonal to this change. Or if it's not possible to neatly separate out that step, I guess that aspect at least should be mentioned and explained in the commit message.

https://github.com/llvm/llvm-project/pull/118035