[AMDGPU] Revert 'Don’t marke the .note section as ALLOC'

[msearles]

Summary

Revert "[AMDGPU] Don’t marke the .note section as ALLOC"

This reverts commit 977cd661cf019039dec7ffdd15bf0ac500828c87.

It breaks OpenCL testing. OpenCL Runtime is using PT_LOAD information
to calculate memory for global variables. This commit should be relanded once
the OpenCL runtime stops relying on PT_LOAD information for calculating global
variable memory size.

[kzhuravl]

LGTM

[nhaehnle]

Hi Mark, do you have more background on this? Is the OpenCL runtime relying on reading something out of the .note section?

[msearles]

TBH, these were Konstantin's findings; he knows the details.

Mark

[t-tye]

The NOTE section is currently being used to hold the high level runtime metadata, and that is only being read by the language runtimes and so does not need to be part of the loaded code object. So I do not think this note section should ever be marked as ALLOC.

I suspect the VDI runtime may be trying to determine how much device memory is available by subtracting the size of the code objects it will load. But it seems it would be better to get the information directly from the runtime memory allocator rather than trying to deduce it indirectly. I think part of the reason it does that may be because currently it is deferring loading code objects until they are first used. I do not think that is the right thing to do either as it means asking for a symbol address of a code object that the application thinks is loaded may fail due to the deferred load failing. It would be better for applications not to load vast numbers of code objects that it will never use (which is why deferred loading was implemented).

llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUTargetStreamer.cpp

void AMDGPUTargetELFStreamer::EmitNote(
     function_ref<void(MCELFStreamer &)> EmitDesc) {
   auto &S = getStreamer();
   auto &Context = S.getContext();
 
   auto NameSZ = Name.size() + 1;
 
   S.PushSection();
   S.SwitchSection(Context.getELFSection(
-    ElfNote::SectionName, ELF::SHT_NOTE, 0));
+    ElfNote::SectionName, ELF::SHT_NOTE, ELF::SHF_ALLOC));
   S.emitIntValue(NameSZ, 4);                                  // namesz
   S.emitValue(DescSZ, 4);                                     // descz
   S.emitIntValue(NoteType, 4);                                // type
   S.emitBytes(Name);                                          // name
   S.emitValueToAlignment(4, 0, 1, 0);                         // padding 0
   EmitDesc(S);                                                // desc
   S.emitValueToAlignment(4, 0, 1, 0);                         // padding 0
   S.PopSection();

llvm/test/CodeGen/AMDGPU/hsa.ll

 ; ELF: Name: .text
 ; ELF: Type: SHT_PROGBITS (0x1)
 ; ELF: Flags [ (0x6)
 ; ELF: SHF_ALLOC (0x2)
 ; ELF: SHF_EXECINSTR (0x4)
 ; ELF: }
 
 ; ELF: SHT_NOTE
-; ELF: Flags [ (0x0)
+; ELF: Flags [ (0x2)
+; ELF: SHF_ALLOC (0x2)
 ; ELF: ]
 ; ELF: SectionData (
 ; ELF: 0000: 04000000 08000000 01000000 414D4400
 ; ELF: 0010: 02000000 01000000 04000000 1B000000
 ; ELF: 0020: 03000000 414D4400 04000700 07000000
 ; ELF: 0030: 00000000 00000000 414D4400 414D4447
 ; ELF: 0040: 50550000
 ; ELF: )