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

[Maksim Panchenko via llvm-commits]

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

>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 1/2] [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

>From 57111b4fab96d32dd5e6b1e4b74a48e02cca0d2b Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks at fb.com>
Date: Fri, 22 Mar 2024 15:15:43 -0700
Subject: [PATCH 2/2] fixup! [BOLT] Skip functions with unsupported Linux
 kernel features

---
 bolt/lib/Rewrite/LinuxKernelRewriter.cpp | 41 +++++++++++-------------
 1 file changed, 18 insertions(+), 23 deletions(-)

diff --git a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
index 21eeecc0cb87fd..42df9681727590 100644
--- a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
+++ b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
@@ -256,6 +256,10 @@ class LinuxKernelRewriter final : public MetadataRewriter {
 
   Error readBugTable();
 
+  /// Do no process functions containing instruction annotated with
+  /// \p Annotation.
+  void skipFunctionsWithAnnotation(StringRef Annotation) const;
+
   /// Handle alternative instruction info from .altinstructions.
   Error readAltInstructions();
   Error rewriteAltInstructions();
@@ -1134,23 +1138,27 @@ Error LinuxKernelRewriter::readParaInstructions() {
   return Error::success();
 }
 
-Error LinuxKernelRewriter::rewriteParaInstructions() {
-  // Disable output of functions with paravirtual instructions before the
-  // rewrite support is complete.
+void LinuxKernelRewriter::skipFunctionsWithAnnotation(
+    StringRef Annotation) const {
   for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
     if (!BC.shouldEmit(BF))
       continue;
     for (const BinaryBasicBlock &BB : BF) {
-      if (!BC.shouldEmit(BF))
+      const bool HasAnnotation = llvm::any_of(BB, [&](const MCInst &Inst) {
+        return BC.MIB->hasAnnotation(Inst, Annotation);
+      });
+      if (HasAnnotation) {
+        BF.setSimple(false);
         break;
-      for (const MCInst &Inst : BB) {
-        if (BC.MIB->hasAnnotation(Inst, "ParaSite")) {
-          BF.setSimple(false);
-          break;
-        }
       }
     }
   }
+}
+
+Error LinuxKernelRewriter::rewriteParaInstructions() {
+  // Disable output of functions with paravirtual instructions before the
+  // rewrite support is complete.
+  skipFunctionsWithAnnotation("ParaSite");
 
   return Error::success();
 }
@@ -1337,20 +1345,7 @@ Error LinuxKernelRewriter::readAltInstructions() {
 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;
-        }
-      }
-    }
-  }
+  skipFunctionsWithAnnotation("AltInst");
 
   return Error::success();
 }