[llvm] [BPF] Add exception handling support with .bpf_cleanup section (PR #192164)

[via llvm-commits]

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@@ -192,6 +193,41 @@ void BPFAsmPrinter::emitInstruction(const MachineInstr *MI) {
   EmitToStreamer(*OutStreamer, TmpInst);
 }
 
+void BPFAsmPrinter::emitFunctionBodyEnd() {
+  // Emit .bpf_cleanup section with a flat table of
+  // (call_site, landing_pad) pairs.
+  const std::vector<LandingPadInfo> &LandingPads = MF->getLandingPads();
+  if (LandingPads.empty())
+    return;
+
+  MCContext &Ctx = OutContext;
+  auto *CleanupSec =
+      Ctx.getELFSection(".bpf_cleanup", ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
+  OutStreamer->switchSection(CleanupSec);
+
+  // Each landing pad has BeginLabels/EndLabels marking the invoke
+  // call sites that unwind to it.
+  for (const LandingPadInfo &LP : LandingPads) {
+    MCSymbol *LPLabel = LP.LandingPadLabel;
+    if (!LPLabel)
+      continue;
+    for (unsigned i = 0, e = LP.BeginLabels.size(); i != e; ++i) {
+      MCSymbol *Begin = LP.BeginLabels[i];
+      MCSymbol *End = LP.EndLabels[i];
+
+      // Each entry is 3 x 4 bytes: begin, end, landing_pad.
+      // The invoke region [begin, end) may include argument setup
+      // before the call. The runtime checks begin <= PC < end.
+      OutStreamer->emitSymbolValue(Begin, 4);
+      OutStreamer->emitSymbolValue(End, 4);
+      OutStreamer->emitSymbolValue(LPLabel, 4);
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eddyz87 wrote:

So, this forgoes type/action table. Is that important for Rust?

https://github.com/llvm/llvm-project/pull/192164