[llvm-objdump] Update offload dumping to use SHT_LLVM_OFFLOADING

[jhuber6]

Summary

In order to be more in-line with ELF semantics, a previous patch added
support for a new ELF section type to indicate if a section contains
offloading data. This allows us to now check using this rather than
checking the section name directly. This patch updates the logic to
check the type now instead.

I chose to make this emit a warning if the input is not an ELF-object
file. I could have made the logic fall-back to the section name, but
this offloading in LLVM is currently not supported on any other targets
so it's probably best to emit a warning until we improve support.

Depends on D129052

[jhenderson]

LGTM, with a couple of suggested tweaks.

If you ever did add support to other object file formats, or you choose to add --offloading to llvm-readobj too, you might want to move the code to fetch the data from an ObjectFile into the ObjectFile interface somewhere, but that's not necessary now. Just something to consider for the future.

llvm/test/tools/llvm-objdump/Offloading/binary.test

7

FWIW, you might want to consider whether it would be useful for llvm-objcopy to be able to create an SHT_LLVM_OFFLOADING section using --set-section-flags, or even by a direct recognition of the name (I imagine it isn't worth it though).

llvm/test/tools/llvm-objdump/Offloading/non-elf.test

15

I'd suggest this slight tweak to the message.

llvm/tools/llvm-objdump/OffloadDump.cpp

20–21

Can you get rid of this now?

[jhuber6]

Removing unused string and updating warning.

[jhuber6]

llvm/test/tools/llvm-objdump/Offloading/binary.test

7

I was expecting llvm-objcopy to have some sort of --set-section-type functionality, maybe that could be added in.

[jhenderson]

llvm/test/tools/llvm-objdump/Offloading/binary.test

7

I don't think I'd be opposed to the idea - it seems much more flexible than the --set-section-flags option.

[MaskRay]

llvm/test/tools/llvm-objdump/Offloading/binary.test

7

I am preparing a patch to add --set-section-type to llvm-objcopy. There was a previous need changing .init_array.N to SHT_INIT_ARRAY. I worked around the issue by using GNU objcopy. Since there are similar needs, maybe time to add it.

llvm/test/tools/llvm-objdump/Offloading/binary.test

 ## Check that we can dump an offloading binary directly.
 # RUN: yaml2obj %S/Inputs/binary.yaml -o %t.bin
 # RUN: llvm-objdump --offloading %t.bin | FileCheck %s --match-full-lines --strict-whitespace --implicit-check-not={{.}}
 
 ## Check that we can dump an offloading binary inside of an ELF section.
 # RUN: yaml2obj %s -o %t.elf
-# RUN: llvm-objcopy --add-section .llvm.offloading=%t.bin %t.elf
-# RUN: llvm-objcopy --set-section-alignment .llvm.offloading=8 %t.elf
+# RUN: llvm-objcopy --update-section .llvm.offloading=%t.bin %t.elf
 # RUN: llvm-objdump --offloading %t.elf | FileCheck %s --check-prefixes=CHECK,ELF --match-full-lines --strict-whitespace --implicit-check-not={{.}}
 
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
+Sections:
+  - Name:            .llvm.offloading
+    Type:            SHT_LLVM_OFFLOADING
+    Flags:           [ SHF_EXCLUDE ]
+    AddressAlign:    0x0000000000000008
 
 #        ELF:{{.*}}file format elf64-unknown
 #  ELF-EMPTY:
 #      CHECK:OFFLOADING IMAGE [0]:
 # CHECK-NEXT:kind            llvm ir
 # CHECK-NEXT:arch            gfx908
 # CHECK-NEXT:triple          amdgcn-amd-amdhsa
 # CHECK-NEXT:producer        openmp

llvm/test/tools/llvm-objdump/Offloading/content-failure.test

 # Test to check if we fail to get the section contents.
 # RUN: yaml2obj %s -o %t
 # RUN: not llvm-objdump --offloading %t 2>&1 | FileCheck -DFILENAME=%t %s
 
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
 Sections:
   - Name:            .llvm.offloading
-    Type:            SHT_PROGBITS
+    Type:            SHT_LLVM_OFFLOADING
     Flags:           [ SHF_EXCLUDE ]
     Address:         0x0
     ShOffset:        0x99999
     AddressAlign:    0x0000000000000008
 
 # CHECK: error: '[[FILENAME]]': The end of the file was unexpectedly encountered

llvm/test/tools/llvm-objdump/Offloading/failure.test

 # RUN: yaml2obj %s -o %t
 # RUN: not llvm-objdump --offloading %t 2>&1 | FileCheck -DFILENAME=%t %s
 
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
 Sections:
   - Name:            .llvm.offloading
-    Type:            SHT_PROGBITS
+    Type:            SHT_LLVM_OFFLOADING
     Flags:           [ SHF_EXCLUDE ]
     Address:         0x0
     AddressAlign:    0x0000000000000008
     Content:         "10ffb0ad"
 
 # CHECK: error: '[[FILENAME]]': while extracting offloading files: Invalid data was encountered while parsing the file

llvm/test/tools/llvm-objdump/Offloading/non-elf.test

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objdump --offloading %t 2>&1 | FileCheck -DFILENAME=%t %s
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .rdata
+    Characteristics: []
+    SectionData:     00
+symbols:
+
+# CHECK: warning: '[[FILENAME]]': --offloading is currently only supported for ELF targets

llvm/test/tools/llvm-objdump/Offloading/warning.test

 ## Ensure we give a warning on bad input following good input.
 # RUN: yaml2obj %S/Inputs/binary.yaml -o %t-good.bin
 # RUN: yaml2obj %S/Inputs/malformed.yaml -o %t-bad.bin
 # RUN: cat %t-bad.bin >> %t-good.bin
 # RUN: yaml2obj %s -o %t.elf
-# RUN: llvm-objcopy --add-section .llvm.offloading=%t-good.bin %t.elf
-# RUN: llvm-objcopy --set-section-alignment .llvm.offloading=8 %t.elf
+# RUN: llvm-objcopy --update-section .llvm.offloading=%t-good.bin %t.elf
 # RUN: llvm-objdump --offloading %t.elf 2>&1 | FileCheck %s -DFILENAME=%t.elf
 
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
+Sections:
+  - Name:            .llvm.offloading
+    Type:            SHT_LLVM_OFFLOADING
+    Flags:           [ SHF_EXCLUDE ]
+    AddressAlign:    0x0000000000000008
 
 # CHECK: OFFLOADING IMAGE [0]:
 # CHECK: warning: '[[FILENAME]]': while parsing offloading files: The end of the file was unexpectedly encountered

llvm/tools/llvm-objdump/OffloadDump.cpp

 //===-- OffloadDump.cpp - Offloading dumper ---------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file implements the offloading-specific dumper for llvm-objdump.
 ///
 //===----------------------------------------------------------------------===//
 #include "OffloadDump.h"
 #include "llvm-objdump.h"
+#include "llvm/Object/ELFObjectFile.h"
 
 using namespace llvm;
 using namespace llvm::object;
 using namespace llvm::objdump;
 
-constexpr const char OffloadSectionString[] = ".llvm.offloading";
-
 /// Get the printable name of the image kind.
 static StringRef getImageName(const OffloadBinary &OB) {
   switch (OB.getImageKind()) {
   case IMG_Object:
     return "elf";
   case IMG_Bitcode:
     return "llvm ir";
   case IMG_Cubin:
     return "cubin";
while (Offset < OB.getMemoryBufferRef().getBufferSize()) {
 
     Offset += Binary.getSize();
   }
   return Error::success();
 }
 
 /// Print the embedded offloading contents of an ObjectFile \p O.
 void llvm::dumpOffloadBinary(const ObjectFile &O) {
-  for (SectionRef Sec : O.sections()) {
-    Expected<StringRef> Name = Sec.getName();
-    if (!Name || !Name->startswith(OffloadSectionString))
+  if (!O.isELF()) {
+    reportWarning("--offloading is currently only supported for ELF targets",
+                  O.getFileName());
+    return;
+  }
+
+  for (ELFSectionRef Sec : O.sections()) {
+    if (Sec.getType() != ELF::SHT_LLVM_OFFLOADING)
       continue;
 
     Expected<StringRef> Contents = Sec.getContents();
     if (!Contents)
       reportError(Contents.takeError(), O.getFileName());
 
     MemoryBufferRef Buffer = MemoryBufferRef(*Contents, O.getFileName());
     auto BinaryOrErr = OffloadBinary::create(Buffer);