[lld] [LLD][COFF] Add support for custom section layout (PR #152779)

[Martin Storsjö via llvm-commits]

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@@ -1413,6 +1415,29 @@ void Writer::removeUnusedSections() {
   llvm::erase_if(ctx.outputSections, isUnused);
 }
 
+void Writer::layoutSections() {
+  llvm::TimeTraceScope timeScope("Layout sections");
+  if (ctx.config.sectionOrder.empty())
+    return;
+
+  llvm::stable_sort(ctx.outputSections,
+                    [this](const OutputSection *a, const OutputSection *b) {
+                      auto itA = ctx.config.sectionOrder.find(a->name.str());
+                      auto itB = ctx.config.sectionOrder.find(b->name.str());
+                      bool aInOrder = itA != ctx.config.sectionOrder.end();
+                      bool bInOrder = itB != ctx.config.sectionOrder.end();
+
+                      // Put unspecified sections after all specified sections
+                      if (aInOrder && bInOrder) {
+                        return itA->second < itB->second;
+                      } else if (aInOrder && !bInOrder) {
+                        return true;
+                      } else {
+                        return false;
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mstorsjo wrote:

I wonder if it'd be good to clarify with a comment, that this both is for the `!aInOrder && bInOrder`, where we explicitly do want one specific order, as complement to the case above, but that we want to treat `!aInOrder && !bInOrder` as equal, i.e. keeping their original order.

https://github.com/llvm/llvm-project/pull/152779