[JITLink] Switch from an atom-based model to a "blocks and symbols" model.

In the Atom model the symbols, content and relocations of a relocatable object
file are represented as a graph of atoms, where each Atom represents a
contiguous block of content with a single name (or no name at all if the
content is anonymous), and where edges between Atoms represent relocations.
If more than one symbol is associated with a contiguous block of content then
the content is broken into multiple atoms and layout constraints (represented by
edges) are introduced to ensure that the content remains effectively contiguous.
These layout constraints must be kept in mind when examining the content
associated with a symbol (it may be spread over multiple atoms) or when applying
certain relocation types (e.g. MachO subtractors).

This patch replaces the Atom model in JITLink with a blocks-and-symbols model.
The blocks-and-symbols model represents relocatable object files as bipartite
graphs, with one set of nodes representing contiguous content (Blocks) and
another representing named or anonymous locations (Symbols) within a Block.
Relocations are represented as edges from Blocks to Symbols. This scheme
removes layout constraints (simplifying handling of MachO alt-entry symbols,
and hopefully ELF sections at some point in the future) and simplifies some
relocation logic.

llvm-svn: 373689

1 files changed, 76 insertions, 63 deletions

diff --git a/llvm/tools/llvm-jitlink/llvm-jitlink-macho.cpp b/llvm/tools/llvm-jitlink/llvm-jitlink-macho.cpp
index 067c38a56cd..9488dfe9b75 100644
--- a/llvm/tools/llvm-jitlink/llvm-jitlink-macho.cpp
+++ b/llvm/tools/llvm-jitlink/llvm-jitlink-macho.cpp
@@ -26,53 +26,55 @@ static bool isMachOStubsSection(Section &S) {
   return S.getName() == "$__STUBS";
 }
 
-static Expected<Edge &> getFirstRelocationEdge(AtomGraph &G, DefinedAtom &DA) {
-  auto EItr = std::find_if(DA.edges().begin(), DA.edges().end(),
+static Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) {
+  auto EItr = std::find_if(B.edges().begin(), B.edges().end(),
                            [](Edge &E) { return E.isRelocation(); });
-  if (EItr == DA.edges().end())
+  if (EItr == B.edges().end())
     return make_error<StringError>("GOT entry in " + G.getName() + ", \"" +
-                                       DA.getSection().getName() +
+                                       B.getSection().getName() +
                                        "\" has no relocations",
                                    inconvertibleErrorCode());
   return *EItr;
 }
 
-static Expected<Atom &> getMachOGOTTarget(AtomGraph &G, DefinedAtom &DA) {
-  auto E = getFirstRelocationEdge(G, DA);
+static Expected<Symbol &> getMachOGOTTarget(LinkGraph &G, Block &B) {
+  auto E = getFirstRelocationEdge(G, B);
   if (!E)
     return E.takeError();
-  auto &TA = E->getTarget();
-  if (!TA.hasName())
-    return make_error<StringError>("GOT entry in " + G.getName() + ", \"" +
-                                       DA.getSection().getName() +
-                                       "\" points to anonymous "
-                                       "atom",
-                                   inconvertibleErrorCode());
-  if (TA.isDefined() || TA.isAbsolute())
+  auto &TargetSym = E->getTarget();
+  if (!TargetSym.hasName())
     return make_error<StringError>(
-        "GOT entry \"" + TA.getName() + "\" in " + G.getName() + ", \"" +
-            DA.getSection().getName() + "\" does not point to an external atom",
+        "GOT entry in " + G.getName() + ", \"" +
+            TargetSym.getBlock().getSection().getName() +
+            "\" points to anonymous "
+            "symbol",
         inconvertibleErrorCode());
-  return TA;
+  if (TargetSym.isDefined() || TargetSym.isAbsolute())
+    return make_error<StringError>(
+        "GOT entry \"" + TargetSym.getName() + "\" in " + G.getName() + ", \"" +
+            TargetSym.getBlock().getSection().getName() +
+            "\" does not point to an external symbol",
+        inconvertibleErrorCode());
+  return TargetSym;
 }
 
-static Expected<Atom &> getMachOStubTarget(AtomGraph &G, DefinedAtom &DA) {
-  auto E = getFirstRelocationEdge(G, DA);
+static Expected<Symbol &> getMachOStubTarget(LinkGraph &G, Block &B) {
+  auto E = getFirstRelocationEdge(G, B);
   if (!E)
     return E.takeError();
-  auto &GOTA = E->getTarget();
-  if (!GOTA.isDefined() ||
-      !isMachOGOTSection(static_cast<DefinedAtom &>(GOTA).getSection()))
-    return make_error<StringError>("Stubs entry in " + G.getName() + ", \"" +
-                                       DA.getSection().getName() +
-                                       "\" does not point to GOT entry",
-                                   inconvertibleErrorCode());
-  return getMachOGOTTarget(G, static_cast<DefinedAtom &>(GOTA));
+  auto &GOTSym = E->getTarget();
+  if (!GOTSym.isDefined() || !isMachOGOTSection(GOTSym.getBlock().getSection()))
+    return make_error<StringError>(
+        "Stubs entry in " + G.getName() + ", \"" +
+            GOTSym.getBlock().getSection().getName() +
+            "\" does not point to GOT entry",
+        inconvertibleErrorCode());
+  return getMachOGOTTarget(G, GOTSym.getBlock());
 }
 
 namespace llvm {
 
-Error registerMachOStubsAndGOT(Session &S, AtomGraph &G) {
+Error registerMachOStubsAndGOT(Session &S, LinkGraph &G) {
   auto FileName = sys::path::filename(G.getName());
   if (S.FileInfos.count(FileName)) {
     return make_error<StringError>("When -check is passed, file names must be "
@@ -88,12 +90,12 @@ Error registerMachOStubsAndGOT(Session &S, AtomGraph &G) {
   for (auto &Sec : G.sections()) {
     LLVM_DEBUG({
       dbgs() << "  Section \"" << Sec.getName() << "\": "
-             << (Sec.atoms_empty() ? "empty. skipping." : "processing...")
+             << (Sec.symbols_empty() ? "empty. skipping." : "processing...")
              << "\n";
     });
 
     // Skip empty sections.
-    if (Sec.atoms_empty())
+    if (Sec.symbols_empty())
       continue;
 
     if (FileInfo.SectionInfos.count(Sec.getName()))
@@ -105,54 +107,65 @@ Error registerMachOStubsAndGOT(Session &S, AtomGraph &G) {
     bool isGOTSection = isMachOGOTSection(Sec);
     bool isStubsSection = isMachOStubsSection(Sec);
 
-    auto *FirstAtom = *Sec.atoms().begin();
-    auto *LastAtom = FirstAtom;
-    for (auto *DA : Sec.atoms()) {
-      if (DA->getAddress() < FirstAtom->getAddress())
-        FirstAtom = DA;
-      if (DA->getAddress() > LastAtom->getAddress())
-        LastAtom = DA;
+    bool SectionContainsContent = false;
+    bool SectionContainsZeroFill = false;
+
+    auto *FirstSym = *Sec.symbols().begin();
+    auto *LastSym = FirstSym;
+    for (auto *Sym : Sec.symbols()) {
+      if (Sym->getAddress() < FirstSym->getAddress())
+        FirstSym = Sym;
+      if (Sym->getAddress() > LastSym->getAddress())
+        LastSym = Sym;
       if (isGOTSection) {
-        if (Sec.isZeroFill())
-          return make_error<StringError>("Content atom in zero-fill section",
+        if (Sym->isSymbolZeroFill())
+          return make_error<StringError>("zero-fill atom in GOT section",
                                          inconvertibleErrorCode());
 
-        if (auto TA = getMachOGOTTarget(G, *DA)) {
-          FileInfo.GOTEntryInfos[TA->getName()] = {DA->getContent(),
-                                                   DA->getAddress()};
-        } else
-          return TA.takeError();
+        if (auto TS = getMachOGOTTarget(G, Sym->getBlock()))
+          FileInfo.GOTEntryInfos[TS->getName()] = {Sym->getSymbolContent(),
+                                                   Sym->getAddress()};
+        else
+          return TS.takeError();
+        SectionContainsContent = true;
       } else if (isStubsSection) {
-        if (Sec.isZeroFill())
-          return make_error<StringError>("Content atom in zero-fill section",
+        if (Sym->isSymbolZeroFill())
+          return make_error<StringError>("zero-fill atom in Stub section",
                                          inconvertibleErrorCode());
 
-        if (auto TA = getMachOStubTarget(G, *DA))
-          FileInfo.StubInfos[TA->getName()] = {DA->getContent(),
-                                               DA->getAddress()};
+        if (auto TS = getMachOStubTarget(G, Sym->getBlock()))
+          FileInfo.StubInfos[TS->getName()] = {Sym->getSymbolContent(),
+                                               Sym->getAddress()};
         else
-          return TA.takeError();
-      } else if (DA->hasName() && DA->isGlobal()) {
-        if (DA->isZeroFill())
-          S.SymbolInfos[DA->getName()] = {DA->getSize(), DA->getAddress()};
-        else {
-          if (Sec.isZeroFill())
-            return make_error<StringError>("Content atom in zero-fill section",
-                                           inconvertibleErrorCode());
-          S.SymbolInfos[DA->getName()] = {DA->getContent(), DA->getAddress()};
+          return TS.takeError();
+        SectionContainsContent = true;
+      } else if (Sym->hasName()) {
+        if (Sym->isSymbolZeroFill()) {
+          S.SymbolInfos[Sym->getName()] = {Sym->getSize(), Sym->getAddress()};
+          SectionContainsZeroFill = true;
+        } else {
+          S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(),
+                                           Sym->getAddress()};
+          SectionContainsContent = true;
         }
       }
     }
 
-    JITTargetAddress SecAddr = FirstAtom->getAddress();
-    uint64_t SecSize = (LastAtom->getAddress() + LastAtom->getSize()) -
-                       FirstAtom->getAddress();
+    JITTargetAddress SecAddr = FirstSym->getAddress();
+    uint64_t SecSize =
+        (LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) -
+        SecAddr;
 
-    if (Sec.isZeroFill())
+    if (SectionContainsZeroFill && SectionContainsContent)
+      return make_error<StringError>("Mixed zero-fill and content sections not "
+                                     "supported yet",
+                                     inconvertibleErrorCode());
+    if (SectionContainsZeroFill)
       FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr};
     else
       FileInfo.SectionInfos[Sec.getName()] = {
-          StringRef(FirstAtom->getContent().data(), SecSize), SecAddr};
+          StringRef(FirstSym->getBlock().getContent().data(), SecSize),
+          SecAddr};
   }
 
   return Error::success();