[llvm] [BOLT] Skip functions with unsupported Linux kernel features (PR #86345)

[Maksim Panchenko via llvm-commits]

https://github.com/maksfb created https://github.com/llvm/llvm-project/pull/86345

Do not overwrite functions with alternative and paravirtual instructions until a proper update support is implemented.

>From 26513312a5d061823afa0c5e780dfe7dc49ecc64 Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks at fb.com>
Date: Fri, 22 Mar 2024 14:34:17 -0700
Subject: [PATCH] [BOLT] Skip functions with unsupported Linux kernel features

Do not overwrite functions with alternative and paravirtual instructions
until a proper update support is implemented.
---
 bolt/lib/Rewrite/LinuxKernelRewriter.cpp | 52 +++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
index 303e8b18fd32ca..21eeecc0cb87fd 100644
--- a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
+++ b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
@@ -252,11 +252,13 @@ class LinuxKernelRewriter final : public MetadataRewriter {
 
   /// Paravirtual instruction patch sites.
   Error readParaInstructions();
+  Error rewriteParaInstructions();
 
   Error readBugTable();
 
-  /// Read alternative instruction info from .altinstructions.
+  /// Handle alternative instruction info from .altinstructions.
   Error readAltInstructions();
+  Error rewriteAltInstructions();
 
   /// Read .pci_fixup
   Error readPCIFixupTable();
@@ -318,6 +320,12 @@ class LinuxKernelRewriter final : public MetadataRewriter {
     if (Error E = rewriteExceptionTable())
       return E;
 
+    if (Error E = rewriteAltInstructions())
+      return E;
+
+    if (Error E = rewriteParaInstructions())
+      return E;
+
     if (Error E = rewriteORCTables())
       return E;
 
@@ -1126,6 +1134,27 @@ Error LinuxKernelRewriter::readParaInstructions() {
   return Error::success();
 }
 
+Error LinuxKernelRewriter::rewriteParaInstructions() {
+  // Disable output of functions with paravirtual instructions before the
+  // rewrite support is complete.
+  for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
+    if (!BC.shouldEmit(BF))
+      continue;
+    for (const BinaryBasicBlock &BB : BF) {
+      if (!BC.shouldEmit(BF))
+        break;
+      for (const MCInst &Inst : BB) {
+        if (BC.MIB->hasAnnotation(Inst, "ParaSite")) {
+          BF.setSimple(false);
+          break;
+        }
+      }
+    }
+  }
+
+  return Error::success();
+}
+
 /// Process __bug_table section.
 /// This section contains information useful for kernel debugging.
 /// Each entry in the section is a struct bug_entry that contains a pointer to
@@ -1305,6 +1334,27 @@ Error LinuxKernelRewriter::readAltInstructions() {
   return Error::success();
 }
 
+Error LinuxKernelRewriter::rewriteAltInstructions() {
+  // Disable output of functions with alt instructions before the rewrite
+  // support is complete.
+  for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
+    if (!BC.shouldEmit(BF))
+      continue;
+    for (const BinaryBasicBlock &BB : BF) {
+      if (!BC.shouldEmit(BF))
+        break;
+      for (const MCInst &Inst : BB) {
+        if (BC.MIB->hasAnnotation(Inst, "AltInst")) {
+          BF.setSimple(false);
+          break;
+        }
+      }
+    }
+  }
+
+  return Error::success();
+}
+
 /// When the Linux kernel needs to handle an error associated with a given PCI
 /// device, it uses a table stored in .pci_fixup section to locate a fixup code
 /// specific to the vendor and the problematic device. The section contains a