commit d8efec97bebd24a3fd12169d9613efc839ba5280
author Yonghong Song <yhs@fb.com> Thu Jul 25 16:01:26 2019 +0000
committer Yonghong Song <yhs@fb.com> Thu Jul 25 16:01:26 2019 +0000
tree 762b953f0475111dea8f0f7193c784f78bb26bc6
parent 5d5a58317cb2512d18d608a97a3a948e708c59e0

[BPF] fix CO-RE incorrect index access string

Currently, we expect the CO-RE offset relocation records
a string encoding the original getelementptr access index,
so kernel bpf loader can decode it correctly.

For example,
  struct s { int a; int b; };
  struct t { int c; int d; };
  #define _(x) (__builtin_preserve_access_index(x))
  int get_value(const void *addr1, const void *addr2);
  int test(struct s *arg1, struct t *arg2) {
    return get_value(_(&arg1->b), _(&arg2->d));
  }

We expect two offset relocations:
  reloc 1: type s, access index 0, 1
  reloc 2: type t, access index 0, 1

Two globals are created to retain access indexes for the
above two relocations with global variable names.
The first global has a name "0:1:". Unfortunately,
the second global has the name "0:1:.1" as the llvm
internals automatically add suffix ".1" to a global
with the same name. Later on, the BPF peels the last
character and record "0:1" and "0:1:." in the
relocation table.

This is not desirable. BPF backend could use the global
variable suffix knowledge to generate correct access str.
This patch rather took an approach not relying on
that knowledge. It generates "s:0:1:" and "t:0:1:" to
avoid global variable suffixes and later on generate
correct index access string "0:1" for both records.

Signed-off-by: Yonghong Song <yhs@fb.com>

Differential Revision: https://reviews.llvm.org/D65258

llvm-svn: 367030

llvm/lib/Target/BPF/BTFDebug.cpp

diff --git a/llvm/lib/Target/BPF/BTFDebug.cpp b/llvm/lib/Target/BPF/BTFDebug.cpp
index fa35c66..3105eae 100644
--- a/llvm/lib/Target/BPF/BTFDebug.cpp
+++ b/llvm/lib/Target/BPF/BTFDebug.cpp
@@ -1006,19 +1006,20 @@
   unsigned RootId = populateStructType(RootTy);
   setTypeFromId(RootId, &PrevStructType, &PrevArrayType);
   unsigned RootTySize = PrevStructType->getStructSize();
+  StringRef IndexPattern = AccessPattern.substr(AccessPattern.find_first_of(':') + 1);
 
   BTFOffsetReloc OffsetReloc;
   OffsetReloc.Label = ORSym;
-  OffsetReloc.OffsetNameOff = addString(AccessPattern.drop_back());
+  OffsetReloc.OffsetNameOff = addString(IndexPattern.drop_back());
   OffsetReloc.TypeID = RootId;
 
   uint32_t Start = 0, End = 0, Offset = 0;
   bool FirstAccess = true;
-  for (auto C : AccessPattern) {
+  for (auto C : IndexPattern) {
     if (C != ':') {
       End++;
     } else {
-      std::string SubStr = AccessPattern.substr(Start, End - Start);
+      std::string SubStr = IndexPattern.substr(Start, End - Start);
       int Loc = std::stoi(SubStr);
 
       if (FirstAccess) {
@@ -1043,7 +1044,7 @@
       End = Start;
     }
   }
-  AccessOffsets[RootTy->getName().str() + ":" + AccessPattern.str()] = Offset;
+  AccessOffsets[AccessPattern.str()] = Offset;
   OffsetRelocTable[SecNameOff].push_back(OffsetReloc);
 }
 
@@ -1227,7 +1228,7 @@
         MDNode *MDN = GVar->getMetadata(LLVMContext::MD_preserve_access_index);
         DIType *Ty = dyn_cast<DIType>(MDN);
         std::string TypeName = Ty->getName();
-        int64_t Imm = AccessOffsets[TypeName + ":" + GVar->getName().str()];
+        int64_t Imm = AccessOffsets[GVar->getName().str()];
 
         // Emit "mov ri, <imm>" for abstract member accesses.
         OutMI.setOpcode(BPF::MOV_ri);