[XRay] Create an Index of sleds per function

Summary:
This change adds a new section to the xray-instrumented binary that
stores an index into ranges of the instrumentation map, where sleds
associated with the same function can be accessed as an array. At
runtime, we can get access to this index by function ID offset allowing
for selective patching and unpatching by function ID.

Each entry in this new section (xray_fn_idx) will include two pointers
indicating the start and one past the end of the sleds associated with
the same function. These entries will be 16 bytes long on x86 and
aarch64. On arm, we align to 16 bytes anyway so the runtime has to take
that into consideration.

__{start,stop}_xray_fn_idx will be the symbols that the runtime will
look for when we implement the selective patching/unpatching by function
id APIs. Because XRay synthesizes the function id's in a monotonically
increasing manner at runtime now, implementations (and users) can use
this table to look up the sleds associated with a specific function.
This is useful in implementations that want to do things like:

  - Implement coverage mode for functions by patching everything
    pre-main, then as functions are encountered, the installed handler
    can unpatch the function that's been encountered after recording
    that it's been called.
  - Do "learning mode", so that the implementation can figure out some
    statistical information about function calls by function id for a
    time being, and then determine which functions are worth
    uninstrumenting at runtime.
  - Do "selective instrumentation" where an implementation can
    specifically instrument only certain function id's at runtime
    (either based on some external data, or through some other
    heuristics) instead of patching all the instrumented functions at
    runtime.

Reviewers: dblaikie, echristo, chandlerc, javed.absar

Subscribers: pelikan, aemerson, kpw, llvm-commits, rengolin

Differential Revision: https://reviews.llvm.org/D32693

llvm-svn: 302109

8 files changed, 93 insertions, 16 deletions

diff --git a/llvm/include/llvm/CodeGen/AsmPrinter.h b/llvm/include/llvm/CodeGen/AsmPrinter.h
index fb8c8408fc7..e008c7ceb06 100644
--- a/llvm/include/llvm/CodeGen/AsmPrinter.h
+++ b/llvm/include/llvm/CodeGen/AsmPrinter.h
@@ -242,7 +242,7 @@ public:
   };
 
   // All the sleds to be emitted.
-  std::vector<XRayFunctionEntry> Sleds;
+  SmallVector<XRayFunctionEntry, 4> Sleds;
 
   // Helper function to record a given XRay sled.
   void recordSled(MCSymbol *Sled, const MachineInstr &MI, SledKind Kind);
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index b11e30c359b..7f38c27f8a9 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -2761,37 +2761,63 @@ void AsmPrinter::emitXRayTable() {
 
   auto PrevSection = OutStreamer->getCurrentSectionOnly();
   auto Fn = MF->getFunction();
-  MCSection *Section = nullptr;
+  MCSection *InstMap = nullptr;
+  MCSection *FnSledIndex = nullptr;
   if (MF->getSubtarget().getTargetTriple().isOSBinFormatELF()) {
     if (Fn->hasComdat()) {
-      Section = OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS,
+      InstMap = OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS,
                                          ELF::SHF_ALLOC | ELF::SHF_GROUP, 0,
                                          Fn->getComdat()->getName());
+      FnSledIndex = OutContext.getELFSection("xray_fn_idx", ELF::SHT_PROGBITS,
+                                             ELF::SHF_ALLOC | ELF::SHF_GROUP, 0,
+                                             Fn->getComdat()->getName());
     } else {
-      Section = OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS,
+      InstMap = OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS,
                                          ELF::SHF_ALLOC);
+      FnSledIndex = OutContext.getELFSection("xray_fn_idx", ELF::SHT_PROGBITS,
+                                             ELF::SHF_ALLOC);
     }
   } else if (MF->getSubtarget().getTargetTriple().isOSBinFormatMachO()) {
-    Section = OutContext.getMachOSection("__DATA", "xray_instr_map", 0,
+    InstMap = OutContext.getMachOSection("__DATA", "xray_instr_map", 0,
                                          SectionKind::getReadOnlyWithRel());
+    FnSledIndex = OutContext.getMachOSection("__DATA", "xray_fn_idx", 0,
+                                             SectionKind::getReadOnlyWithRel());
   } else {
     llvm_unreachable("Unsupported target");
   }
 
   // Before we switch over, we force a reference to a label inside the
-  // xray_instr_map section. Since this function is always called just
-  // before the function's end, we assume that this is happening after
-  // the last return instruction.
-
+  // xray_instr_map and xray_fn_idx sections. Since this function is always
+  // called just before the function's end, we assume that this is happening
+  // after the last return instruction. We also use the synthetic label in the
+  // xray_inster_map as a delimeter for the range of sleds for this function in
+  // the index.
   auto WordSizeBytes = MAI->getCodePointerSize();
-  MCSymbol *Tmp = OutContext.createTempSymbol("xray_synthetic_", true);
+  MCSymbol *SledsStart = OutContext.createTempSymbol("xray_synthetic_", true);
+  MCSymbol *IdxRef = OutContext.createTempSymbol("xray_fn_idx_synth_", true);
   OutStreamer->EmitCodeAlignment(16);
-  OutStreamer->EmitSymbolValue(Tmp, WordSizeBytes, false);
-  OutStreamer->SwitchSection(Section);
-  OutStreamer->EmitLabel(Tmp);
+  OutStreamer->EmitSymbolValue(SledsStart, WordSizeBytes, false);
+  OutStreamer->EmitSymbolValue(IdxRef, WordSizeBytes, false);
+
+  // Now we switch to the instrumentation map section. Because this is done
+  // per-function, we are able to create an index entry that will represent the
+  // range of sleds associated with a function.
+  OutStreamer->SwitchSection(InstMap);
+  OutStreamer->EmitLabel(SledsStart);
   for (const auto &Sled : Sleds)
     Sled.emit(WordSizeBytes, OutStreamer.get(), CurrentFnSym);
-
+  MCSymbol *SledsEnd = OutContext.createTempSymbol("xray_synthetic_end", true);
+  OutStreamer->EmitLabel(SledsEnd);
+
+  // We then emit a single entry in the index per function. We use the symbols
+  // that bound the instrumentation map as the range for a specific function.
+  // Each entry here will be 16-byte aligned, as we're writing down two
+  // pointers.
+  OutStreamer->SwitchSection(FnSledIndex);
+  OutStreamer->EmitCodeAlignment(16);
+  OutStreamer->EmitLabel(IdxRef);
+  OutStreamer->EmitSymbolValue(SledsStart, WordSizeBytes);
+  OutStreamer->EmitSymbolValue(SledsEnd, WordSizeBytes);
   OutStreamer->SwitchSection(PrevSection);
   Sleds.clear();
 }
diff --git a/llvm/test/CodeGen/AArch64/xray-attribute-instrumentation.ll b/llvm/test/CodeGen/AArch64/xray-attribute-instrumentation.ll
index d0f5f40e156..38b62a72a20 100644
--- a/llvm/test/CodeGen/AArch64/xray-attribute-instrumentation.ll
+++ b/llvm/test/CodeGen/AArch64/xray-attribute-instrumentation.ll
@@ -26,6 +26,7 @@ define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always"
 }
 ; CHECK:       .p2align 4
 ; CHECK-NEXT:  .xword .Lxray_synthetic_0
+; CHECK-NEXT:  .xword .Lxray_fn_idx_synth_0
 ; CHECK-NEXT:  .section xray_instr_map,{{.*}}
 ; CHECK-LABEL: Lxray_synthetic_0:
 ; CHECK:       .xword .Lxray_sled_0
diff --git a/llvm/test/CodeGen/AArch64/xray-tail-call-sled.ll b/llvm/test/CodeGen/AArch64/xray-tail-call-sled.ll
index 6ada3ce8d55..fb89950b99c 100644
--- a/llvm/test/CodeGen/AArch64/xray-tail-call-sled.ll
+++ b/llvm/test/CodeGen/AArch64/xray-tail-call-sled.ll
@@ -29,10 +29,16 @@ define i32 @callee() nounwind noinline uwtable "function-instrument"="xray-alway
 }

 ; CHECK:       .p2align 4

 ; CHECK-NEXT:  .xword .Lxray_synthetic_0

+; CHECK-NEXT:  .xword .Lxray_fn_idx_synth_0

 ; CHECK-NEXT:  .section xray_instr_map,{{.*}}

 ; CHECK-LABEL: Lxray_synthetic_0:

 ; CHECK:       .xword .Lxray_sled_0

 ; CHECK:       .xword .Lxray_sled_1

+; CHECK-LABEL: Lxray_synthetic_end0:

+; CHECK:       .section xray_fn_idx,{{.*}}

+; CHECK-LABEL: Lxray_fn_idx_synth_0:

+; CHECK:       .xword .Lxray_synthetic_0

+; CHECK-NEXT:  .xword .Lxray_synthetic_end0

 

 define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-always" {

 ; CHECK:       .p2align	2

@@ -63,7 +69,13 @@ define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-alway
 }

 ; CHECK:       .p2align 4

 ; CHECK-NEXT:  .xword .Lxray_synthetic_1

+; CHECK-NEXT:  .xword .Lxray_fn_idx_synth_1

 ; CHECK-NEXT:  .section xray_instr_map,{{.*}}

 ; CHECK-LABEL: Lxray_synthetic_1:

 ; CHECK:       .xword .Lxray_sled_2

 ; CHECK:       .xword .Lxray_sled_3

+; CHECK-LABEL: Lxray_synthetic_end1:

+; CHECK:       .section xray_fn_idx,{{.*}}

+; CHECK-LABEL: Lxray_fn_idx_synth_1:

+; CHECK:       .xword .Lxray_synthetic_1

+; CHECK-NEXT:  .xword .Lxray_synthetic_end1

diff --git a/llvm/test/CodeGen/ARM/xray-armv6-attribute-instrumentation.ll b/llvm/test/CodeGen/ARM/xray-armv6-attribute-instrumentation.ll
index 93c3cb14fb7..5e3c45c3454 100644
--- a/llvm/test/CodeGen/ARM/xray-armv6-attribute-instrumentation.ll
+++ b/llvm/test/CodeGen/ARM/xray-armv6-attribute-instrumentation.ll
@@ -25,7 +25,13 @@ define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always"
 }
 ; CHECK:       .p2align 4
 ; CHECK-NEXT:  .long {{.*}}Lxray_synthetic_0
+; CHECK-NEXT:  .long {{.*}}Lxray_fn_idx_synth_0
 ; CHECK-NEXT:  .section {{.*}}xray_instr_map{{.*}}
 ; CHECK-LABEL: Lxray_synthetic_0:
 ; CHECK:       .long {{.*}}Lxray_sled_0
 ; CHECK:       .long {{.*}}Lxray_sled_1
+; CHECK-LABEL: Lxray_synthetic_end0:
+; CHECK:       .section {{.*}}xray_fn_idx{{.*}}
+; CHECK-LABEL: Lxray_fn_idx_synth_0:
+; CHECK:       .long {{.*}}Lxray_synthetic_0
+; CHECK-NEXT:  .long {{.*}}Lxray_synthetic_end0
diff --git a/llvm/test/CodeGen/ARM/xray-armv7-attribute-instrumentation.ll b/llvm/test/CodeGen/ARM/xray-armv7-attribute-instrumentation.ll
index d14590b8867..739151fbdd5 100644
--- a/llvm/test/CodeGen/ARM/xray-armv7-attribute-instrumentation.ll
+++ b/llvm/test/CodeGen/ARM/xray-armv7-attribute-instrumentation.ll
@@ -25,7 +25,14 @@ define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always"
 }
 ; CHECK:       .p2align 4
 ; CHECK-NEXT:  .long {{.*}}Lxray_synthetic_0
+; CHECK-NEXT:  .long {{.*}}Lxray_fn_idx_synth_0
 ; CHECK-NEXT:  .section {{.*}}xray_instr_map{{.*}}
 ; CHECK-LABEL: Lxray_synthetic_0:
 ; CHECK:       .long {{.*}}Lxray_sled_0
 ; CHECK:       .long {{.*}}Lxray_sled_1
+; CHECK-LABEL: Lxray_synthetic_end0:
+; CHECK:       .section {{.*}}xray_fn_idx{{.*}}
+; CHECK-LABEL: Lxray_fn_idx_synth_0:
+; CHECK:       .long {{.*}}xray_synthetic_0
+; CHECK-NEXT:  .long {{.*}}xray_synthetic_end0
+
diff --git a/llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll b/llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll
index c52ccf9356b..7c60327d2c3 100644
--- a/llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll
+++ b/llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll
@@ -15,10 +15,17 @@ define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always"
 }
 ; CHECK:       .p2align 4, 0x90
 ; CHECK-NEXT:  .quad {{.*}}xray_synthetic_0
+; CHECK-NEXT:  .quad {{.*}}xray_fn_idx_synth_0
 ; CHECK-NEXT:  .section {{.*}}xray_instr_map
 ; CHECK-LABEL: Lxray_synthetic_0:
 ; CHECK:       .quad {{.*}}xray_sled_0
 ; CHECK:       .quad {{.*}}xray_sled_1
+; CHECK-LABEL: Lxray_synthetic_end0:
+; CHECK:       .section {{.*}}xray_fn_idx
+; CHECK-LABEL: Lxray_fn_idx_synth_0:
+; CHECK:       .quad {{.*}}xray_synthetic_0
+; CHECK-NEXT:  .quad {{.*}}xray_synthetic_end0
+
 
 ; We test multiple returns in a single function to make sure we're getting all
 ; of them with XRay instrumentation.
@@ -46,8 +53,14 @@ NotEqual:
 }
 ; CHECK:       .p2align 4, 0x90
 ; CHECK-NEXT:  .quad {{.*}}xray_synthetic_1
+; CHECK-NEXT:  .quad {{.*}}xray_fn_idx_synth_1
 ; CHECK-NEXT:  .section {{.*}}xray_instr_map
 ; CHECK-LABEL: Lxray_synthetic_1:
 ; CHECK:       .quad {{.*}}xray_sled_2
 ; CHECK:       .quad {{.*}}xray_sled_3
 ; CHECK:       .quad {{.*}}xray_sled_4
+; CHECK-LABEL: Lxray_synthetic_end1:
+; CHECK:       .section {{.*}}xray_fn_idx
+; CHECK-LABEL: Lxray_fn_idx_synth_1:
+; CHECK:       .quad {{.*}}xray_synthetic_1
+; CHECK-NEXT:  .quad {{.*}}xray_synthetic_end1
diff --git a/llvm/test/CodeGen/X86/xray-tail-call-sled.ll b/llvm/test/CodeGen/X86/xray-tail-call-sled.ll
index ece786a5e80..b12c78a77b2 100644
--- a/llvm/test/CodeGen/X86/xray-tail-call-sled.ll
+++ b/llvm/test/CodeGen/X86/xray-tail-call-sled.ll
@@ -14,11 +14,17 @@ define i32 @callee() nounwind noinline uwtable "function-instrument"="xray-alway
 ; CHECK-NEXT:  nopw %cs:512(%rax,%rax)
 }
 ; CHECK:       .p2align 4, 0x90
-; CHECK-NEXT:  .quad {{.*}}xray_synthetic_0
+; CHECK-NEXT:  .quad {{.*}}xray_synthetic_0{{.*}}
+; CHECK-NEXT:  .quad {{.*}}xray_fn_idx_synth_0{{.*}}
 ; CHECK-NEXT:  .section {{.*}}xray_instr_map
 ; CHECK-LABEL: Lxray_synthetic_0:
 ; CHECK:       .quad {{.*}}xray_sled_0
 ; CHECK:       .quad {{.*}}xray_sled_1
+; CHECK-LABEL: Lxray_synthetic_end0:
+; CHECK-NEXT:  .section {{.*}}xray_fn_idx
+; CHECK-LABEL: Lxray_fn_idx_synth_0:
+; CHECK:       .quad {{.*}}xray_synthetic_0
+; CHECK-NEXT:  .quad {{.*}}xray_synthetic_end0
 
 define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-always" {
 ; CHECK:       .p2align 1, 0x90
@@ -36,7 +42,13 @@ define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-alway
   ret i32 %retval
 }
 ; CHECK:       .p2align 4, 0x90
-; CHECK-NEXT:  .quad {{.*}}xray_synthetic_1
+; CHECK-NEXT:  .quad {{.*}}xray_synthetic_1{{.*}}
+; CHECK-NEXT:  .quad {{.*}}xray_fn_idx_synth_1{{.*}}
 ; CHECK-LABEL: Lxray_synthetic_1:
 ; CHECK:       .quad {{.*}}xray_sled_2
 ; CHECK:       .quad {{.*}}xray_sled_3
+; CHECK-LABEL: Lxray_synthetic_end1:
+; CHECK:       .section {{.*}}xray_fn_idx
+; CHECK-LABEL: Lxray_fn_idx_synth_1:
+; CHECK:       .quad {{.*}}xray_synthetic_1
+; CHECK:       .quad {{.*}}xray_synthetic_end1