[XRay] ARM 32-bit no-Thumb support in LLVM
This is a port of XRay to ARM 32-bit, without Thumb support yet. The XRay instrumentation support is moving up to AsmPrinter.
This is one of 3 commits to different repositories of XRay ARM port. The other 2 are:
1. https://reviews.llvm.org/D23932 (Clang test)
2. https://reviews.llvm.org/D23933 (compiler-rt)
Differential Revision: https://reviews.llvm.org/D23931
llvm-svn: 280888
diff --git a/llvm/lib/Target/ARM/ARMMCInstLower.cpp b/llvm/lib/Target/ARM/ARMMCInstLower.cpp
index 7429acd..afdde4e 100644
--- a/llvm/lib/Target/ARM/ARMMCInstLower.cpp
+++ b/llvm/lib/Target/ARM/ARMMCInstLower.cpp
@@ -21,6 +21,11 @@
#include "llvm/IR/Mangler.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCSymbolELF.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCInstBuilder.h"
+#include "llvm/MC/MCStreamer.h"
using namespace llvm;
@@ -150,3 +155,85 @@
}
}
}
+
+void ARMAsmPrinter::EmitSled(const MachineInstr &MI, SledKind Kind)
+{
+ static const int8_t NoopsInSledCount = 6;
+ // We want to emit the following pattern:
+ //
+ // .Lxray_sled_N:
+ // ALIGN
+ // B #20
+ // ; 6 NOP instructions (24 bytes)
+ // .tmpN
+ //
+ // We need the 24 bytes (6 instructions) because at runtime, we'd be patching
+ // over the full 28 bytes (7 instructions) with the following pattern:
+ //
+ // PUSH{ r0, lr }
+ // MOVW r0, #<lower 16 bits of function ID>
+ // MOVT r0, #<higher 16 bits of function ID>
+ // MOVW ip, #<lower 16 bits of address of __xray_FunctionEntry/Exit>
+ // MOVT ip, #<higher 16 bits of address of __xray_FunctionEntry/Exit>
+ // BLX ip
+ // POP{ r0, lr }
+ //
+ OutStreamer->EmitCodeAlignment(4);
+ auto CurSled = OutContext.createTempSymbol("xray_sled_", true);
+ OutStreamer->EmitLabel(CurSled);
+ auto Target = OutContext.createTempSymbol();
+
+ // Emit "B #20" instruction, which jumps over the next 24 bytes (because
+ // register pc is 8 bytes ahead of the jump instruction by the moment CPU
+ // is executing it).
+ // By analogy to ARMAsmPrinter::emitPseudoExpansionLowering() |case ARM::B|.
+ // It is not clear why |addReg(0)| is needed (the last operand).
+ EmitToStreamer(*OutStreamer, MCInstBuilder(ARM::Bcc).addImm(20)
+ .addImm(ARMCC::AL).addReg(0));
+
+ MCInst Noop;
+ Subtarget->getInstrInfo()->getNoopForElfTarget(Noop);
+ for (int8_t I = 0; I < NoopsInSledCount; I++)
+ {
+ OutStreamer->EmitInstruction(Noop, getSubtargetInfo());
+ }
+
+ OutStreamer->EmitLabel(Target);
+ recordSled(CurSled, MI, Kind);
+}
+
+void ARMAsmPrinter::LowerPATCHABLE_FUNCTION_ENTER(const MachineInstr &MI)
+{
+ EmitSled(MI, SledKind::FUNCTION_ENTER);
+}
+
+void ARMAsmPrinter::LowerPATCHABLE_FUNCTION_EXIT(const MachineInstr &MI)
+{
+ EmitSled(MI, SledKind::FUNCTION_EXIT);
+}
+
+void ARMAsmPrinter::EmitXRayTable()
+{
+ if (Sleds.empty())
+ return;
+ if (Subtarget->isTargetELF()) {
+ auto *Section = OutContext.getELFSection(
+ "xray_instr_map", ELF::SHT_PROGBITS,
+ ELF::SHF_ALLOC | ELF::SHF_GROUP | ELF::SHF_MERGE, 0,
+ CurrentFnSym->getName());
+ auto PrevSection = OutStreamer->getCurrentSectionOnly();
+ OutStreamer->SwitchSection(Section);
+ for (const auto &Sled : Sleds) {
+ OutStreamer->EmitSymbolValue(Sled.Sled, 4);
+ OutStreamer->EmitSymbolValue(CurrentFnSym, 4);
+ auto Kind = static_cast<uint8_t>(Sled.Kind);
+ OutStreamer->EmitBytes(
+ StringRef(reinterpret_cast<const char *>(&Kind), 1));
+ OutStreamer->EmitBytes(
+ StringRef(reinterpret_cast<const char *>(&Sled.AlwaysInstrument), 1));
+ OutStreamer->EmitZeros(6);
+ }
+ OutStreamer->SwitchSection(PrevSection);
+ }
+ Sleds.clear();
+}