[llvm] 5af9e64 - [JITLink][AArch46] Update aarch64 pointer jump stub sequence, add utilities.

[Lang Hames via llvm-commits]

Author: Lang Hames
Date: 2022-10-31T08:41:20-07:00
New Revision: 5af9e648ae10c50d94ab169f65907e12f210ec99

URL: https://github.com/llvm/llvm-project/commit/5af9e648ae10c50d94ab169f65907e12f210ec99
DIFF: https://github.com/llvm/llvm-project/commit/5af9e648ae10c50d94ab169f65907e12f210ec99.diff

LOG: [JITLink][AArch46] Update aarch64 pointer jump stub sequence, add utilities.

Updates the aarch64 pointer jump stub sequence to:

ADRP x16, <ptr>@page21
LDR  x16, [x16, <ptr>@pageoff12]
BR   x16

from:

LDR  x16, <ptr>@ldrimm19
BR   x16

The old sequence can only reference pointers within +/-1Mb, which may not be
enough for large object files. The new sequence can reach pointers within
+/-4Gb. (A future pre-fixup-pass could apply range-based optimizations to
turn this into an ldr-br-nop sequence.)

Also adds createPointerJumpStubBlock and createAnonymousPointerJumpStub
utilities along the same lines as their x86-64 counterparts.

The PLTTableManager is updated to use the new utility functions.

Added: 
    

Modified: 
    llvm/include/llvm/ExecutionEngine/JITLink/aarch64.h
    llvm/lib/ExecutionEngine/JITLink/aarch64.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/ExecutionEngine/JITLink/aarch64.h b/llvm/include/llvm/ExecutionEngine/JITLink/aarch64.h
index efd1eed080e33..33c09e1a2a315 100644
--- a/llvm/include/llvm/ExecutionEngine/JITLink/aarch64.h
+++ b/llvm/include/llvm/ExecutionEngine/JITLink/aarch64.h
@@ -481,8 +481,14 @@ constexpr uint64_t PointerSize = 8;
 /// AArch64 null pointer content.
 extern const char NullPointerContent[PointerSize];
 
-/// AArch64 PLT stub content.
-extern const uint8_t StubContent[8];
+/// AArch64 pointer jump stub content.
+///
+/// Contains the instruction sequence for an indirect jump via an in-memory
+/// pointer:
+///   ADRP x16, ptr at page21
+///   LDR  x16, [x16, ptr at pageoff12]
+///   BR   x16
+extern const char PointerJumpStubContent[12];
 
 /// Creates a new pointer block in the given section and returns an
 /// Anonymous symobl pointing to it.
@@ -504,6 +510,33 @@ inline Symbol &createAnonymousPointer(LinkGraph &G, Section &PointerSection,
   return G.addAnonymousSymbol(B, 0, 8, false, false);
 }
 
+/// Create a jump stub block that jumps via the pointer at the given symbol.
+///
+/// The stub block will have the following default values:
+///   alignment: 32-bit
+///   alignment-offset: 0
+///   address: highest allowable: (~11U)
+inline Block &createPointerJumpStubBlock(LinkGraph &G, Section &StubSection,
+                                         Symbol &PointerSymbol) {
+  auto &B = G.createContentBlock(StubSection, PointerJumpStubContent,
+                                 orc::ExecutorAddr(~uint64_t(11)), 1, 0);
+  B.addEdge(Page21, 0, PointerSymbol, 0);
+  B.addEdge(PageOffset12, 4, PointerSymbol, 0);
+  return B;
+}
+
+/// Create a jump stub that jumps via the pointer at the given symbol and
+/// an anonymous symbol pointing to it. Return the anonymous symbol.
+///
+/// The stub block will be created by createPointerJumpStubBlock.
+inline Symbol &createAnonymousPointerJumpStub(LinkGraph &G,
+                                              Section &StubSection,
+                                              Symbol &PointerSymbol) {
+  return G.addAnonymousSymbol(
+      createPointerJumpStubBlock(G, StubSection, PointerSymbol), 0,
+      sizeof(PointerJumpStubContent), true, false);
+}
+
 /// Global Offset Table Builder.
 class GOTTableManager : public TableManager<GOTTableManager> {
 public:
@@ -586,12 +619,8 @@ class PLTTableManager : public TableManager<PLTTableManager> {
   }
 
   Symbol &createEntry(LinkGraph &G, Symbol &Target) {
-    auto &StubContentBlock = G.createContentBlock(
-        getStubsSection(G), getStubBlockContent(), orc::ExecutorAddr(), 1, 0);
-    // Re-use GOT entries for stub targets.
-    auto &GOTEntrySymbol = GOT.getEntryForTarget(G, Target);
-    StubContentBlock.addEdge(aarch64::LDRLiteral19, 0, GOTEntrySymbol, 0);
-    return G.addAnonymousSymbol(StubContentBlock, 0, 8, true, false);
+    return createAnonymousPointerJumpStub(G, getStubsSection(G),
+                                          GOT.getEntryForTarget(G, Target));
   }
 
 public:
@@ -602,10 +631,6 @@ class PLTTableManager : public TableManager<PLTTableManager> {
     return *StubsSection;
   }
 
-  ArrayRef<char> getStubBlockContent() {
-    return {reinterpret_cast<const char *>(StubContent), sizeof(StubContent)};
-  }
-
   GOTTableManager &GOT;
   Section *StubsSection = nullptr;
 };

diff  --git a/llvm/lib/ExecutionEngine/JITLink/aarch64.cpp b/llvm/lib/ExecutionEngine/JITLink/aarch64.cpp
index d51416d0ddf0e..1011fa81f750f 100644
--- a/llvm/lib/ExecutionEngine/JITLink/aarch64.cpp
+++ b/llvm/lib/ExecutionEngine/JITLink/aarch64.cpp
@@ -21,9 +21,10 @@ namespace aarch64 {
 const char NullPointerContent[8] = {0x00, 0x00, 0x00, 0x00,
                                     0x00, 0x00, 0x00, 0x00};
 
-const uint8_t StubContent[8] = {
-    0x10, 0x00, 0x00, 0x58, // LDR x16, <literal>
-    0x00, 0x02, 0x1f, 0xd6  // BR  x16
+const char PointerJumpStubContent[12] = {
+    0x10, 0x00, 0x00, (char)0x90u, // ADRP x16, <imm>@page21
+    0x10, 0x02, 0x40, (char)0xf9u, // LDR x16, [x16, <imm>@pageoff12]
+    0x00, 0x02, 0x1f, (char)0xd6u  // BR  x16
 };
 
 const char *getEdgeKindName(Edge::Kind R) {