Fix PR22408 - LLVM producing AArch64 TLS relocations that GNU linkers cannot handle yet.

As is described at http://llvm.org/bugs/show_bug.cgi?id=22408, the GNU linkers
ld.bfd and ld.gold currently only support a subset of the whole range of AArch64
ELF TLS relocations. Furthermore, they assume that some of the code sequences to
access thread-local variables are produced in a very specific sequence.
When the sequence is not as the linker expects, it can silently mis-relaxe/mis-optimize
the instructions.
Even if that wouldn't be the case, it's good to produce the exact sequence,
as that ensures that linkers can perform optimizing relaxations.

This patch:

* implements support for 16MiB TLS area size instead of 4GiB TLS area size. Ideally clang
  would grow an -mtls-size option to allow support for both, but that's not part of this patch.
* by default doesn't produce local dynamic access patterns, as even modern ld.bfd and ld.gold
  linkers do not support the associated relocations. An option (-aarch64-elf-ldtls-generation)
  is added to enable generation of local dynamic code sequence, but is off by default.
* makes sure that the exact expected code sequence for local dynamic and general dynamic
  accesses is produced, by making use of a new pseudo instruction. The patch also removes
  two (AArch64ISD::TLSDESC_BLR, AArch64ISD::TLSDESC_CALL) pre-existing AArch64-specific pseudo
  SDNode instructions that are superseded by the new one (TLSDESC_CALLSEQ).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231227 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 47 insertions, 12 deletions

diff --git a/lib/Target/AArch64/AArch64AsmPrinter.cpp b/lib/Target/AArch64/AArch64AsmPrinter.cpp
index d64d8515bd9..5367f90f7c1 100644
--- a/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -12,6 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "MCTargetDesc/AArch64AddressingModes.h"
+#include "MCTargetDesc/AArch64MCExpr.h"
 #include "AArch64.h"
 #include "AArch64MCInstLower.h"
 #include "AArch64MachineFunctionInfo.h"
@@ -489,24 +491,57 @@ void AArch64AsmPrinter::EmitInstruction(const MachineInstr *MI) {
     EmitToStreamer(OutStreamer, TmpInst);
     return;
   }
-  case AArch64::TLSDESC_BLR: {
-    MCOperand Callee, Sym;
-    MCInstLowering.lowerOperand(MI->getOperand(0), Callee);
-    MCInstLowering.lowerOperand(MI->getOperand(1), Sym);
-
-    // First emit a relocation-annotation. This expands to no code, but requests
+  case AArch64::TLSDESC_CALLSEQ: {
+    /// lower this to:
+    ///    adrp  x0, :tlsdesc:var
+    ///    ldr   x1, [x0, #:tlsdesc_lo12:var]
+    ///    add   x0, x0, #:tlsdesc_lo12:var
+    ///    .tlsdesccall var
+    ///    blr   x1
+    ///    (TPIDR_EL0 offset now in x0)
+    const MachineOperand &MO_Sym = MI->getOperand(0);
+    MachineOperand MO_TLSDESC_LO12(MO_Sym), MO_TLSDESC(MO_Sym);
+    MCOperand Sym, SymTLSDescLo12, SymTLSDesc;
+    MO_TLSDESC_LO12.setTargetFlags(AArch64II::MO_TLS | AArch64II::MO_PAGEOFF |
+                                   AArch64II::MO_NC);
+    MO_TLSDESC.setTargetFlags(AArch64II::MO_TLS | AArch64II::MO_PAGE);
+    MCInstLowering.lowerOperand(MO_Sym, Sym);
+    MCInstLowering.lowerOperand(MO_TLSDESC_LO12, SymTLSDescLo12);
+    MCInstLowering.lowerOperand(MO_TLSDESC, SymTLSDesc);
+
+    MCInst Adrp;
+    Adrp.setOpcode(AArch64::ADRP);
+    Adrp.addOperand(MCOperand::CreateReg(AArch64::X0));
+    Adrp.addOperand(SymTLSDesc);
+    EmitToStreamer(OutStreamer, Adrp);
+
+    MCInst Ldr;
+    Ldr.setOpcode(AArch64::LDRXui);
+    Ldr.addOperand(MCOperand::CreateReg(AArch64::X1));
+    Ldr.addOperand(MCOperand::CreateReg(AArch64::X0));
+    Ldr.addOperand(SymTLSDescLo12);
+    Ldr.addOperand(MCOperand::CreateImm(0));
+    EmitToStreamer(OutStreamer, Ldr);
+
+    MCInst Add;
+    Add.setOpcode(AArch64::ADDXri);
+    Add.addOperand(MCOperand::CreateReg(AArch64::X0));
+    Add.addOperand(MCOperand::CreateReg(AArch64::X0));
+    Add.addOperand(SymTLSDescLo12);
+    Add.addOperand(MCOperand::CreateImm(AArch64_AM::getShiftValue(0)));
+    EmitToStreamer(OutStreamer, Add);
+
+    // Emit a relocation-annotation. This expands to no code, but requests
     // the following instruction gets an R_AARCH64_TLSDESC_CALL.
     MCInst TLSDescCall;
     TLSDescCall.setOpcode(AArch64::TLSDESCCALL);
     TLSDescCall.addOperand(Sym);
     EmitToStreamer(OutStreamer, TLSDescCall);
 
-    // Other than that it's just a normal indirect call to the function loaded
-    // from the descriptor.
-    MCInst BLR;
-    BLR.setOpcode(AArch64::BLR);
-    BLR.addOperand(Callee);
-    EmitToStreamer(OutStreamer, BLR);
+    MCInst Blr;
+    Blr.setOpcode(AArch64::BLR);
+    Blr.addOperand(MCOperand::CreateReg(AArch64::X1));
+    EmitToStreamer(OutStreamer, Blr);
 
     return;
   }