[llvm-branch-commits] [llvm] [GOFF] Add writing of section symbols (PR #133799)

[Ulrich Weigand via llvm-branch-commits]

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+//===- MCGOFFAttributes.h - Attributes of GOFF symbols --------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the various attribute collections defining GOFF symbols.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCGOFFATTRIBUTES_H
+#define LLVM_MC_MCGOFFATTRIBUTES_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/BinaryFormat/GOFF.h"
+
+namespace llvm {
+namespace GOFF {
+// An "External Symbol Definition" in the GOFF file has a type, and depending on
+// the type a different subset of the fields is used.
+//
+// Unlike other formats, a 2 dimensional structure is used to define the
+// location of data. For example, the equivalent of the ELF .text section is
+// made up of a Section Definition (SD) and a class (Element Definition; ED).
+// The name of the SD symbol depends on the application, while the class has the
+// predefined name C_CODE/C_CODE64 in AMODE31 and AMODE64 respectively.
+//
+// Data can be placed into this structure in 2 ways. First, the data (in a text
+// record) can be associated with an ED symbol. To refer to data, a Label
+// Definition (LD) is used to give an offset into the data a name. When binding,
+// the whole data is pulled into the resulting executable, and the addresses
+// given by the LD symbols are resolved.
+//
+// The alternative is to use a Part Definition (PR). In this case, the data (in
+// a text record) is associated with the part. When binding, only the data of
+// referenced PRs is pulled into the resulting binary.
+//
+// Both approaches are used, which means that the equivalent of a section in ELF
+// results in 3 GOFF symbols, either SD/ED/LD or SD/ED/PR. Moreover, certain
+// sections are fine with just defining SD/ED symbols. The SymbolMapper takes
+// care of all those details.
+
+// Attributes for SD symbols.
+struct SDAttr {
+  GOFF::ESDTaskingBehavior TaskingBehavior = GOFF::ESD_TA_Unspecified;
+  GOFF::ESDBindingScope BindingScope = GOFF::ESD_BSC_Unspecified;
+};
+
+// Attributes for ED symbols.
+struct EDAttr {
+  bool IsReadOnly = false;
+  GOFF::ESDExecutable Executable = GOFF::ESD_EXE_Unspecified;
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uweigand wrote:

According to the GOFF docs, while the executable flag is supported on ED, it's only purpose is to act as default for the executable flags in all LDs defined in this ED.   Assuming we set the flag in the LDs, do we also need it in the ED?

https://github.com/llvm/llvm-project/pull/133799