[lld] ELF: Introduce --randomize-section-padding option. (PR #117653)

[via llvm-commits]

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@@ -1444,6 +1444,38 @@ static void finalizeSynthetic(Ctx &ctx, SyntheticSection *sec) {
   }
 }
 
+static bool canInsertPadding(OutputSection *sec) {
+  StringRef s = sec->name;
+  return s == ".bss" || s == ".data" || s == ".data.rel.ro" || s == ".rodata" ||
+         s.starts_with(".text");
+}
+
+static void shufflePadding(Ctx &ctx) {
+  std::mt19937 g(*ctx.arg.shufflePadding);
+  PhdrEntry *curPtLoad = nullptr;
+  for (OutputSection *os : ctx.outputSections) {
+    if (!canInsertPadding(os))
+      continue;
+    for (SectionCommand *bc : os->commands) {
+      if (auto *isd = dyn_cast<InputSectionDescription>(bc)) {
+        SmallVector<InputSection *, 0> tmp;
+        if (os->ptLoad != curPtLoad) {
+          tmp.push_back(
+              make<ShufflePaddingSection>(ctx, g() % ctx.arg.maxPageSize, os));
+          curPtLoad = os->ptLoad;
+        }
+        for (InputSection *isec : isd->sections) {
+          if (g() < (1 << 28))
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pcc wrote:

I added a comment and made this a bit less magical (use modulus instead). I'm not sure we need to make it configurable from the start. In the future, if/when we make it configurable, we can just make 1 in 16 the default.

https://github.com/llvm/llvm-project/pull/117653