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

[Kai Nacke via llvm-branch-commits]

redstar wrote:

> Does this make sense or am I missing something here?

I think that splitting the SD/ED/LD into 3 "section"s implies that a MCSectionGOFF has a fundamentally different semantic than the other MCSectionXXX. This is something I would like to avoid. On the other hand, the SD/ED pair is almost the same as an ELF section, so just putting those 2 into a MCSectionGOFF instance and handling the LD/PR symbol differently makes sense. In HLASM, a section definition looks like
```
HLASMHEL CSECT                        * The SD symbol
HLASMHEL AMODE 64
HLASMHEL RMODE ANY
C_CODE64 CATTR EXECUTABLE,RENT        * The ED symbol; the LD symbol is automatically generated.
         ENTRY MAIN
MAIN     AMODE 64
MAIN     XATTR LINKAGE(XPLINK),SCOPE(LIBRARY),REFERENCE(CODE)
MAIN     DS    0FD                    * A "normal" label, with attributes. Results in another LD symbol
```

When I switch sections, and later want to continue the code section, then I need to repeat both statements in a short form:

```
HLASMHEL CSECT ,
C_CODE64 CATTR ,
```

I thought about this when moving the definitions from the SymbolMapper to the MCObjectFileInfo class, but I got no good idea how to handle the LD or PR symbol. A possible way could be to attach the LD or PR symbol as the begin symbol of a section. I need to try this.

One possible downside is that it makes handling of relocations much more complicated. For the base of a relocation, I need the PR symbol (when I have the SD/ED/PR case) or the LD and ED (in the SD/ED/LD case). Currently, this information is available in the MCSectionGOFF, without the need to chase a list to the correct element.

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