[BOLT] Add ORC validation for the Linux kernel

[maksfb]

The Linux kernel expects ORC tables to be sorted by IP address (for binary search to work). Add a post-emit pass in LinuxKernelRewriter that validates the written .orc_unwind_ip against that expectation.

[llvmbot]

@llvm/pr-subscribers-bolt

Author: Maksim Panchenko (maksfb)

Changes

The Linux kernel expects ORC tables to be sorted by IP address (for binary search to work). Add a post-emit pass in LinuxKernelRewriter that validates the written .orc_unwind_ip against that expectation.

---

Full diff: https://github.com/llvm/llvm-project/pull/90660.diff

1 Files Affected:

• (modified) bolt/lib/Rewrite/LinuxKernelRewriter.cpp (+31)

diff --git a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
index d96199e020d31a..3944bb742938a7 100644
--- a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
+++ b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
@@ -248,6 +248,9 @@ class LinuxKernelRewriter final : public MetadataRewriter {
   /// Update ORC data in the binary.
   Error rewriteORCTables();
 
+  /// Validate written ORC tables after binary emission.
+  Error validateORCTables();
+
   /// Static call table handling.
   Error readStaticCalls();
   Error rewriteStaticCalls();
@@ -358,6 +361,9 @@ class LinuxKernelRewriter final : public MetadataRewriter {
     if (Error E = updateStaticKeysJumpTablePostEmit())
       return E;
 
+    if (Error E = validateORCTables())
+      return E;
+
     return Error::success();
   }
 };
@@ -837,6 +843,31 @@ Error LinuxKernelRewriter::rewriteORCTables() {
   return Error::success();
 }
 
+Error LinuxKernelRewriter::validateORCTables() {
+  if (!ORCUnwindIPSection)
+    return Error::success();
+
+  const uint64_t IPSectionAddress = ORCUnwindIPSection->getAddress();
+  DataExtractor IPDE = DataExtractor(ORCUnwindIPSection->getOutputContents(),
+                                     BC.AsmInfo->isLittleEndian(),
+                                     BC.AsmInfo->getCodePointerSize());
+  DataExtractor::Cursor IPCursor(0);
+  uint64_t PrevIP = 0;
+  for (uint32_t Index = 0; Index < NumORCEntries; ++Index) {
+    const uint64_t IP =
+        IPSectionAddress + IPCursor.tell() + (int32_t)IPDE.getU32(IPCursor);
+    if (!IPCursor)
+      return createStringError(errc::executable_format_error,
+                               "out of bounds while reading ORC IP table: %s",
+                               toString(IPCursor.takeError()).c_str());
+
+    assert(IP >= PrevIP && "Unsorted ORC table detected");
+    PrevIP = IP;
+  }
+
+  return Error::success();
+}
+
 /// The static call site table is created by objtool and contains entries in the
 /// following format:
 ///

[dcci]

Thanks.