[PATCH] D88339: [XCOFF] Enable -fdata-sections on AIX

[David Tenty via Phabricator via llvm-commits]

daltenty added inline comments.


================
Comment at: llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp:1992
           ->getQualNameSymbol();
-    if (GOKind.isCommon() || GOKind.isBSSLocal())
+    if (GOKind.isCommon() || GOKind.isBSSLocal() || TM.getDataSections())
       return cast<MCSectionXCOFF>(SectionForGlobal(GO, GOKind, TM))
----------------
We're currently gating this behavior on the code-gen data-sections option, but AIX common initialization does really function correctly without it, so we should probably adopt this as a default.

Summarizing from off-list discussion:

Variables with common linkage will be emitted as a common-type csect in XCOFF. Per the assembly reference: 

//"Several modules can share the same common block. If any of those modules have an external Control Section (csect) with the same name and the csect with the same name has a storage mapping class other than BS or UC, then the common block is initialized and becomes that other Control Section.”//

Initialization via a non-csect (i.e label-ed data) is not defined, and results in a linker warning:
```
$ cat common.s
.comm foo, 2
$ cat label.s
.csect data[RW]
.globl foo
foo:
        .vbyte 2,0
__start:
        nop
.globl __start
$ ld common.o label.o
ld: 0711-224 WARNING: Duplicate symbol: foo
ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information.
```


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D88339/new/

https://reviews.llvm.org/D88339