Notify the linker when a TU compiled with split-stack has a functionwithout a prologue.There is more context here:https://go-review.googlesource.com/c/go/+/148819/

[saugustine]

Summary

Notify the linker when a TU compiled with split-stack
has a function without a prologue.

[echristo]

Test?

[saugustine]

Add a test case.

[echristo]

LGTM.

lib/Target/ARM/ARMFrameLowering.cpp

2166

FTR the casing on NosplitStack here really bugs me, but it's not your fault and can be updated later :)

[saugustine]

Committed as r347614.

lib/Target/ARM/ARMFrameLowering.cpp

const ARMBaseInstrInfo &TII =
       *static_cast<const ARMBaseInstrInfo *>(MF.getSubtarget().getInstrInfo());
   ARMFunctionInfo *ARMFI = MF.getInfo<ARMFunctionInfo>();
   DebugLoc DL;
 
   uint64_t StackSize = MFI.getStackSize();
 
   // Do not generate a prologue for leaf functions with a stack of size zero.
   // For non-leaf functions we have to allow for the possibility that the
-  // call is to a non-split function, as in PR37807.
-  if (StackSize == 0 && !MFI.hasTailCall())
+  // callis to a non-split function, as in PR37807. This function could also
+  // take the address of a non-split function. When the linker tries to adjust
+  // its non-existent prologue, it would fail with an error. Mark the object
+  // file so that such failures are not errors. See this Go language bug-report
+  // https://go-review.googlesource.com/c/go/+/148819/
+  if (StackSize == 0 && !MFI.hasTailCall()) {
+    MF.getMMI().setHasNosplitStack(true);
     return;
+  }
 
   // Use R4 and R5 as scratch registers.
   // We save R4 and R5 before use and restore them before leaving the function.
   unsigned ScratchReg0 = ARM::R4;
   unsigned ScratchReg1 = ARM::R5;
   uint64_t AlignedStackSize;
 
   MachineBasicBlock *PrevStackMBB = MF.CreateMachineBasicBlock();

lib/Target/X86/X86FrameLowering.cpp

void X86FrameLowering::adjustForSegmentedStacks(
 
   // Eventually StackSize will be calculated by a link-time pass; which will
   // also decide whether checking code needs to be injected into this particular
   // prologue.
   StackSize = MFI.getStackSize();
 
   // Do not generate a prologue for leaf functions with a stack of size zero.
   // For non-leaf functions we have to allow for the possibility that the
-  // call is to a non-split function, as in PR37807.
-  if (StackSize == 0 && !MFI.hasTailCall())
+  // callis to a non-split function, as in PR37807. This function could also
+  // take the address of a non-split function. When the linker tries to adjust
+  // its non-existent prologue, it would fail with an error. Mark the object
+  // file so that such failures are not errors. See this Go language bug-report
+  // https://go-review.googlesource.com/c/go/+/148819/
+  if (StackSize == 0 && !MFI.hasTailCall()) {
+    MF.getMMI().setHasNosplitStack(true);
     return;
+  }
 
   MachineBasicBlock *allocMBB = MF.CreateMachineBasicBlock();
   MachineBasicBlock *checkMBB = MF.CreateMachineBasicBlock();
   X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
   bool IsNested = false;
 
   // We need to know if the function has a nest argument only in 64 bit mode.
   if (Is64Bit)

test/CodeGen/X86/segmented-stacks-standalone.ll

+; RUN: llc < %s -mcpu=generic -mtriple=i686-linux -verify-machineinstrs | FileCheck %s -check-prefix=X32-Linux
+; RUN: llc < %s -mcpu=generic -mtriple=x86_64-linux  -verify-machineinstrs | FileCheck %s -check-prefix=X64-Linux
+
+; This test is standalone because segmented-stacks.ll generates
+; object-files with both .note.GNU-split-stack (for the split-stack
+; functions) and .note.GNU-no-split-stack sections (for the
+; non-split-stack functions). But a split-stack function without a
+; stack frame should have a .note.GNU-split-stack section regardless
+; of any other contents of the compilation unit.
+
+define void @test_nostack() #0 {
+  ret void
+}
+
+attributes #0 = { "split-stack" }
+
+; X32-Linux: .section ".note.GNU-split-stack","",@progbits
+; X32-Linux: .section ".note.GNU-no-split-stack","",@progbits
+
+; X64-Linux: .section ".note.GNU-split-stack","",@progbits
+; X64-Linux: .section ".note.GNU-no-split-stack","",@progbits
+
+; X64-FreeBSD: .section ".note.GNU-split-stack","",@progbits
+; X64-FreeBSD: .section ".note.GNU-no-split-stack","",@progbits
+
+; X32-DFlyBSD: .section ".note.GNU-split-stack","",@progbits
+; X32-DFlyBSD: .section ".note.GNU-no-split-stack","",@progbits
+
+; X64-DFlyBSD: .section ".note.GNU-split-stack","",@progbits
+; X64-DFlyBSD: .section ".note.GNU-no-split-stack","",@progbits