commit d46a6a9e6865ef71f754d8bcaae5205cf484856d
author Yonghong Song <yhs@fb.com> Thu Oct 10 15:33:09 2019 +0000
committer Yonghong Song <yhs@fb.com> Thu Oct 10 15:33:09 2019 +0000
tree 08aadd8d663a62a88d6fbad47898da3c93330baa
parent 4abac53302775af3c5ed396883207b5b45ba030f

[BPF] Remove relocation for patchable externs

Previously, patchable extern relocations are introduced to patch
external variables used for multi versioning in
compile once, run everywhere use case. The load instruction
will be converted into a move with an patchable immediate
which can be changed by bpf loader on the host.

The kernel verifier has evolved and is able to load
and propagate constant values, so compiler relocation
becomes unnecessary. This patch removed codes related to this.

Differential Revision: https://reviews.llvm.org/D68760

llvm-svn: 374367

llvm/lib/Target/BPF/BTFDebug.cpp

diff --git a/llvm/lib/Target/BPF/BTFDebug.cpp b/llvm/lib/Target/BPF/BTFDebug.cpp
index a8f8573..db551e7 100644
--- a/llvm/lib/Target/BPF/BTFDebug.cpp
+++ b/llvm/lib/Target/BPF/BTFDebug.cpp
@@ -752,9 +752,10 @@
 }
 
 void BTFDebug::emitBTFExtSection() {
-  // Do not emit section if empty FuncInfoTable and LineInfoTable.
+  // Do not emit section if empty FuncInfoTable and LineInfoTable
+  // and FieldRelocTable.
   if (!FuncInfoTable.size() && !LineInfoTable.size() &&
-      !FieldRelocTable.size() && !ExternRelocTable.size())
+      !FieldRelocTable.size())
     return;
 
   MCContext &Ctx = OS.getContext();
@@ -766,8 +767,8 @@
 
   // Account for FuncInfo/LineInfo record size as well.
   uint32_t FuncLen = 4, LineLen = 4;
-  // Do not account for optional FieldReloc/ExternReloc.
-  uint32_t FieldRelocLen = 0, ExternRelocLen = 0;
+  // Do not account for optional FieldReloc.
+  uint32_t FieldRelocLen = 0;
   for (const auto &FuncSec : FuncInfoTable) {
     FuncLen += BTF::SecFuncInfoSize;
     FuncLen += FuncSec.second.size() * BTF::BPFFuncInfoSize;
@@ -780,15 +781,9 @@
     FieldRelocLen += BTF::SecFieldRelocSize;
     FieldRelocLen += FieldRelocSec.second.size() * BTF::BPFFieldRelocSize;
   }
-  for (const auto &ExternRelocSec : ExternRelocTable) {
-    ExternRelocLen += BTF::SecExternRelocSize;
-    ExternRelocLen += ExternRelocSec.second.size() * BTF::BPFExternRelocSize;
-  }
 
   if (FieldRelocLen)
     FieldRelocLen += 4;
-  if (ExternRelocLen)
-    ExternRelocLen += 4;
 
   OS.EmitIntValue(0, 4);
   OS.EmitIntValue(FuncLen, 4);
@@ -796,8 +791,6 @@
   OS.EmitIntValue(LineLen, 4);
   OS.EmitIntValue(FuncLen + LineLen, 4);
   OS.EmitIntValue(FieldRelocLen, 4);
-  OS.EmitIntValue(FuncLen + LineLen + FieldRelocLen, 4);
-  OS.EmitIntValue(ExternRelocLen, 4);
 
   // Emit func_info table.
   OS.AddComment("FuncInfo");
@@ -848,22 +841,6 @@
       }
     }
   }
-
-  // Emit extern reloc table.
-  if (ExternRelocLen) {
-    OS.AddComment("ExternReloc");
-    OS.EmitIntValue(BTF::BPFExternRelocSize, 4);
-    for (const auto &ExternRelocSec : ExternRelocTable) {
-      OS.AddComment("Extern reloc section string offset=" +
-                    std::to_string(ExternRelocSec.first));
-      OS.EmitIntValue(ExternRelocSec.first, 4);
-      OS.EmitIntValue(ExternRelocSec.second.size(), 4);
-      for (const auto &ExternRelocInfo : ExternRelocSec.second) {
-        Asm->EmitLabelReference(ExternRelocInfo.Label, 4);
-        OS.EmitIntValue(ExternRelocInfo.ExternNameOff, 4);
-      }
-    }
-  }
 }
 
 void BTFDebug::beginFunctionImpl(const MachineFunction *MF) {
@@ -1019,15 +996,6 @@
       MDNode *MDN = GVar->getMetadata(LLVMContext::MD_preserve_access_index);
       DIType *Ty = dyn_cast<DIType>(MDN);
       generateFieldReloc(MI, ORSym, Ty, GVar->getName());
-    } else if (GVar && !GVar->hasInitializer() && GVar->hasExternalLinkage() &&
-               GVar->getSection() == BPFCoreSharedInfo::PatchableExtSecName) {
-      MCSymbol *ORSym = OS.getContext().createTempSymbol();
-      OS.EmitLabel(ORSym);
-
-      BTFExternReloc ExternReloc;
-      ExternReloc.Label = ORSym;
-      ExternReloc.ExternNameOff = addString(GVar->getName());
-      ExternRelocTable[SecNameOff].push_back(ExternReloc);
     }
   }
 }
@@ -1165,20 +1133,6 @@
         OutMI.addOperand(MCOperand::createReg(MI->getOperand(0).getReg()));
         OutMI.addOperand(MCOperand::createImm(Imm));
         return true;
-      } else if (GVar && !GVar->hasInitializer() &&
-                 GVar->hasExternalLinkage() &&
-                 GVar->getSection() == BPFCoreSharedInfo::PatchableExtSecName) {
-        const IntegerType *IntTy = dyn_cast<IntegerType>(GVar->getValueType());
-        assert(IntTy);
-        // For patchable externals, emit "LD_imm64, ri, 0" if the external
-        // variable is 64bit width, emit "mov ri, 0" otherwise.
-        if (IntTy->getBitWidth() == 64)
-          OutMI.setOpcode(BPF::LD_imm64);
-        else
-          OutMI.setOpcode(BPF::MOV_ri);
-        OutMI.addOperand(MCOperand::createReg(MI->getOperand(0).getReg()));
-        OutMI.addOperand(MCOperand::createImm(0));
-        return true;
       }
     }
   }