[llvm-jitlink] Support plain AArch32 range extension stubs in jitlink-check's stub_addr() expressions

llvm/include/llvm/ExecutionEngine/JITLink/aarch32.h

@@ -295,7 +295,7 @@ class StubsManager : public TableManager<StubsManager<Flavor>> {
   StubsManager() = default;
 
   /// Name of the object file section that will contain all our stubs.
-  static StringRef getSectionName() { return "__llvm_jitlink_STUBS"; }
+  static StringRef getSectionName();
 
   /// Implements link-graph traversal via visitExistingEdges().
   bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
@@ -345,6 +345,10 @@ class StubsManager : public TableManager<StubsManager<Flavor>> {
 template <>
 Symbol &StubsManager<Thumbv7>::createEntry(LinkGraph &G, Symbol &Target);
 
+template <> inline StringRef StubsManager<Thumbv7>::getSectionName() {
+  return "__llvm_jitlink_aarch32_STUBS_Thumbv7";
+}
+
 } // namespace aarch32
 } // namespace jitlink
 } // namespace llvm

llvm/test/ExecutionEngine/JITLink/AArch32/ELF_thumb_stubs.s

@@ -0,0 +1,45 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc -triple=thumbv7-linux-gnueabi -arm-add-build-attributes \
+# RUN:         -filetype=obj -filetype=obj -o %t/elf_stubs.o %s
+# RUN: llvm-jitlink -noexec -slab-address 0x76ff0000 \
+# RUN:              -slab-allocate 10Kb -slab-page-size 4096 \
+# RUN:              -abs external_func=0x76bbe880 \
+# RUN:              -check %s %t/elf_stubs.o
+
+	.text
+	.syntax unified
+
+# Check that calls/jumps to external functions trigger the generation of
+# branch-range extension stubs. These stubs don't follow the default PLT model
+# where the branch-target address is loaded from a GOT entry. Instead, they
+# hard-code it in the immediate field.
+#
+# jitlink-check: decode_operand(test_external_call, 2) = stub_addr(elf_stubs.o, external_func) - next_pc(test_external_call)
+# jitlink-check: decode_operand(test_external_jump, 0) = stub_addr(elf_stubs.o, external_func) - next_pc(test_external_jump)
+	.globl  test_external_call
+	.type	test_external_call,%function
+	.p2align	1
+	.code	16
+	.thumb_func
+test_external_call:
+	bl	external_func
+	.size test_external_call, .-test_external_call
+
+	.globl  test_external_jump
+	.type	test_external_call,%function
+	.p2align	1
+	.code	16
+	.thumb_func
+test_external_jump:
+	b	external_func
+	.size test_external_jump, .-test_external_jump
+
+# Empty main function for jitlink to be happy
+	.globl	main
+	.type	main,%function
+	.p2align	1
+	.code	16
+	.thumb_func
+main:
+	bx	lr
+	.size	main,	.-main

llvm/tools/llvm-jitlink/llvm-jitlink-elf.cpp

@@ -24,6 +24,10 @@ static bool isELFGOTSection(Section &S) { return S.getName() == "$__GOT"; }
 
 static bool isELFStubsSection(Section &S) { return S.getName() == "$__STUBS"; }
 
+static bool isELFAArch32StubsSection(Section &S) {
+  return S.getName().starts_with("__llvm_jitlink_aarch32_STUBS_");
+}
+
 static Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) {
   auto EItr =
       llvm::find_if(B.edges(), [](Edge &E) { return E.isRelocation(); });
@@ -64,6 +68,15 @@ static Expected<Symbol &> getELFStubTarget(LinkGraph &G, Block &B) {
   return getELFGOTTarget(G, GOTSym.getBlock());
 }
 
+static Expected<std::string> getELFAArch32StubTargetName(LinkGraph &G,
+                                                         Block &B) {
+  auto E = getFirstRelocationEdge(G, B);
+  if (!E)
+    return E.takeError();
+  Symbol &StubTarget = E->getTarget();
+  return StubTarget.getName().str();
+}
+
 namespace llvm {
 
 Error registerELFGraphInfo(Session &S, LinkGraph &G) {
@@ -98,6 +111,7 @@ Error registerELFGraphInfo(Session &S, LinkGraph &G) {
 
     bool isGOTSection = isELFGOTSection(Sec);
     bool isStubsSection = isELFStubsSection(Sec);
+    bool isAArch32StubsSection = isELFAArch32StubsSection(Sec);
 
     bool SectionContainsContent = false;
     bool SectionContainsZeroFill = false;
@@ -138,6 +152,18 @@ Error registerELFGraphInfo(Session &S, LinkGraph &G) {
         else
           return TS.takeError();
         SectionContainsContent = true;
+      } else if (isAArch32StubsSection) {
+        if (Sym->isSymbolZeroFill())
+          return make_error<StringError>("zero-fill atom in Stub section",
+                                         inconvertibleErrorCode());
+
+        if (auto Name = getELFAArch32StubTargetName(G, Sym->getBlock()))
+          FileInfo.StubInfos[*Name] = {Sym->getSymbolContent(),
+                                       Sym->getAddress().getValue(),
+                                       Sym->getTargetFlags()};
+        else
+          return Name.takeError();
+        SectionContainsContent = true;
       }
 
       if (Sym->hasName()) {