[llvm] r291431 - RuntimeDyldELF: don't create thunk if not needed
Eugene Leviant via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 9 01:56:31 PST 2017
Author: evgeny777
Date: Mon Jan 9 03:56:31 2017
New Revision: 291431
URL: http://llvm.org/viewvc/llvm-project?rev=291431&view=rev
Log:
RuntimeDyldELF: don't create thunk if not needed
This patch doesn't create thunk for branch operation when following conditions are met:
- Architecture is AArch64
- Relocation target is in the same object file
- Relocation target is close enough to be encoded in immediate offset
In such case we branch directly to the target instead of branching to thunk
Differential revision: https://reviews.llvm.org/D28108
Added:
llvm/trunk/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_local_branch.s
Modified:
llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
Modified: llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp?rev=291431&r1=291430&r2=291431&view=diff
==============================================================================
--- llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp (original)
+++ llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp Mon Jan 9 03:56:31 2017
@@ -896,6 +896,49 @@ uint32_t RuntimeDyldELF::getMatchingLoRe
return ELF::R_MIPS_NONE;
}
+// Sometimes we don't need to create thunk for a branch.
+// This typically happens when branch target is located
+// in the same object file. In such case target is either
+// a weak symbol or symbol in a different executable section.
+// This function checks if branch target is located in the
+// same object file and if distance between source and target
+// fits R_AARCH64_CALL26 relocation. If both conditions are
+// met, it emits direct jump to the target and returns true.
+// Otherwise false is returned and thunk is created.
+bool RuntimeDyldELF::resolveAArch64ShortBranch(
+ unsigned SectionID, relocation_iterator RelI,
+ const RelocationValueRef &Value) {
+ uint64_t Address;
+ if (Value.SymbolName) {
+ auto Loc = GlobalSymbolTable.find(Value.SymbolName);
+
+ // Don't create direct branch for external symbols.
+ if (Loc == GlobalSymbolTable.end())
+ return false;
+
+ const auto &SymInfo = Loc->second;
+ Address = reinterpret_cast<uint64_t>(
+ Sections[SymInfo.getSectionID()].getLoadAddressWithOffset(
+ SymInfo.getOffset()));
+ } else {
+ Address =
+ reinterpret_cast<uint64_t>(Sections[Value.SectionID].getLoadAddress());
+ }
+ uint64_t Offset = RelI->getOffset();
+ uint64_t SourceAddress = Sections[SectionID].getLoadAddressWithOffset(Offset);
+
+ // R_AARCH64_CALL26 requires immediate to be in range -2^27 <= imm < 2^27
+ // If distance between source and target is out of range then we should
+ // create thunk.
+ if (!isInt<28>(Address + Value.Addend - SourceAddress))
+ return false;
+
+ resolveRelocation(Sections[SectionID], Offset, Address, RelI->getType(),
+ Value.Addend);
+
+ return true;
+}
+
Expected<relocation_iterator>
RuntimeDyldELF::processRelocationRef(
unsigned SectionID, relocation_iterator RelI, const ObjectFile &O,
@@ -1003,7 +1046,7 @@ RuntimeDyldELF::processRelocationRef(
(uint64_t)Section.getAddressWithOffset(i->second),
RelType, 0);
DEBUG(dbgs() << " Stub function found\n");
- } else {
+ } else if (!resolveAArch64ShortBranch(SectionID, RelI, Value)) {
// Create a new stub function.
DEBUG(dbgs() << " Create a new stub function\n");
Stubs[Value] = Section.getStubOffset();
Modified: llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h?rev=291431&r1=291430&r2=291431&view=diff
==============================================================================
--- llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h (original)
+++ llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h Mon Jan 9 03:56:31 2017
@@ -40,6 +40,9 @@ class RuntimeDyldELF : public RuntimeDyl
void resolveAArch64Relocation(const SectionEntry &Section, uint64_t Offset,
uint64_t Value, uint32_t Type, int64_t Addend);
+ bool resolveAArch64ShortBranch(unsigned SectionID, relocation_iterator RelI,
+ const RelocationValueRef &Value);
+
void resolveARMRelocation(const SectionEntry &Section, uint64_t Offset,
uint32_t Value, uint32_t Type, int32_t Addend);
Added: llvm/trunk/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_local_branch.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_local_branch.s?rev=291431&view=auto
==============================================================================
--- llvm/trunk/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_local_branch.s (added)
+++ llvm/trunk/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_local_branch.s Mon Jan 9 03:56:31 2017
@@ -0,0 +1,14 @@
+# RUN: llvm-mc -triple=arm64-none-linux-gnu -filetype=obj -o %T/branch.o %s
+# RUN: llvm-rtdyld -triple=arm64-none-linux-gnu -verify -check=%s %T/branch.o
+
+.globl _main
+.weak _label1
+
+.section .text.1,"ax"
+_label1:
+ nop
+_main:
+ b _label1
+
+## Branch 1 instruction back from _main
+# rtdyld-check: *{4}(_main) = 0x17ffffff
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