[BOLT] Set cold sections alignment explicitly

The cold text section alignment is set using the maximum alignment value
passed to the emitCodeAlignment. In order to calculate tentetive layout
right we will set the minimum alignment of such sections to the maximum
possible function alignment explicitly.

Differential Revision: https://reviews.llvm.org/D121392

Author: yota9

bolt/include/bolt/Utils/CommandLineOpts.h

@@ -30,6 +30,7 @@ extern llvm::cl::OptionCategory BoltInstrCategory;
 extern llvm::cl::OptionCategory HeatmapCategory;
 
 extern llvm::cl::opt<unsigned> AlignText;
+extern llvm::cl::opt<unsigned> AlignFunctions;
 extern llvm::cl::opt<bool> AggregateOnly;
 extern llvm::cl::opt<unsigned> BucketsPerLine;
 extern llvm::cl::opt<bool> DiffOnly;

bolt/lib/Core/BinaryEmitter.cpp

@@ -291,6 +291,12 @@ bool BinaryEmitter::emitFunction(BinaryFunction &Function, bool EmitColdPart) {
   BC.Ctx->addGenDwarfSection(Section);
 
   if (BC.HasRelocations) {
+    // Set section alignment to at least maximum possible object alignment.
+    // We need this to support LongJmp and other passes that calculates
+    // tentative layout.
+    if (Section->getAlignment() < opts::AlignFunctions)
+      Section->setAlignment(Align(opts::AlignFunctions));
+
     Streamer.emitCodeAlignment(BinaryFunction::MinAlign, &*BC.STI);
     uint16_t MaxAlignBytes = EmitColdPart ? Function.getMaxColdAlignmentBytes()
                                           : Function.getMaxAlignmentBytes();

bolt/lib/Passes/Aligner.cpp

@@ -23,6 +23,7 @@ extern cl::OptionCategory BoltOptCategory;
 
 extern cl::opt<bool> AlignBlocks;
 extern cl::opt<bool> PreserveBlocksAlignment;
+extern cl::opt<unsigned> AlignFunctions;
 
 cl::opt<unsigned>
 AlignBlocksMinSize("align-blocks-min-size",
@@ -43,13 +44,6 @@ AlignBlocksThreshold("align-blocks-threshold",
   cl::Hidden,
   cl::cat(BoltOptCategory));
 
-cl::opt<unsigned>
-AlignFunctions("align-functions",
-  cl::desc("align functions at a given value (relocation mode)"),
-  cl::init(64),
-  cl::ZeroOrMore,
-  cl::cat(BoltOptCategory));
-
 cl::opt<unsigned>
 AlignFunctionsMaxBytes("align-functions-max-bytes",
   cl::desc("maximum number of bytes to use to align functions"),

bolt/lib/Passes/LongJmp.cpp

@@ -11,15 +11,14 @@
 //===----------------------------------------------------------------------===//
 
 #include "bolt/Passes/LongJmp.h"
-#include "llvm/Support/Alignment.h"
 
 #define DEBUG_TYPE "longjmp"
 
 using namespace llvm;
 
 namespace opts {
 extern cl::OptionCategory BoltOptCategory;
-
+extern cl::opt<unsigned> AlignFunctions;
 extern cl::opt<bool> UseOldText;
 extern cl::opt<bool> HotFunctionsAtEnd;
 
@@ -295,6 +294,7 @@ void LongJmpPass::tentativeBBLayout(const BinaryFunction &Func) {
 uint64_t LongJmpPass::tentativeLayoutRelocColdPart(
     const BinaryContext &BC, std::vector<BinaryFunction *> &SortedFunctions,
     uint64_t DotAddress) {
+  DotAddress = alignTo(DotAddress, llvm::Align(opts::AlignFunctions));
   for (BinaryFunction *Func : SortedFunctions) {
     if (!Func->isSplit())
       continue;

bolt/lib/Utils/CommandLineOpts.cpp

@@ -42,6 +42,11 @@ AlignText("align-text",
   cl::Hidden,
   cl::cat(BoltCategory));
 
+cl::opt<unsigned> AlignFunctions(
+    "align-functions",
+    cl::desc("align functions at a given value (relocation mode)"),
+    cl::init(64), cl::ZeroOrMore, cl::cat(BoltOptCategory));
+
 cl::opt<bool>
 AggregateOnly("aggregate-only",
   cl::desc("exit after writing aggregated data file"),