[XCOFF] set fragment for XMC_PR csects.

[Esme]

Summary

-xcoff-traceback-table is a default option on AIX regardless of optimization and debug levels. An error of relocation for paired relocatable term is not yet supported in XCOFFObjectWriter::recordRelocation occurred when both of the -xcoff-traceback-table and -function-sections are enabled.
The root cause is that we missed to calculate the symbols difference as absolute value before adding fixups when symbol_A without the fragment set is the csect itself and symbol_B is in it.
This patch only sets the fragment for XMC_PR csects because we don't have other cases that hit this problem yet.

[Esme]

Clean test failure.

[hubert.reinterpretcast]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

2223 ↗

(On Diff #472873)

Can we address this where the MCExpr is handled instead? There may be more ways a similar expression involving a csect as an operand is involved in the future (e.g., assembly parsing).

[DiggerLin]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

2223 ↗

(On Diff #472873)

I do not think we should set setFragment of FuncSectSym in the function emitTracebackTable.
Reason as :

1. because of both Asm path and "integrated-as" enter into the function emitTracebackTable. Asm path do not have Fragment concept.
2. the emitTracebackTable only do emit trace back table related thing. we should not put other functionality here.

I think we may need to set the

The fragment value to CurrentFnSym of AsmPrinter in somewhere when "integrated-as"
otherwise the CurrentFnSym.isUndefined() is true.

it will cause the function MCExpr::evaluateAsRelocatableImpl() return "false" when evaluation the fixup of CurrentFnSym-FuncEnd

[DiggerLin]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

2223 ↗

(On Diff #472873)

maybe you can try to set the fragment of QualName in the function MCSectionXCOFF *MCContext::getXCOFFSection.

   if (Begin)
     Begin->setFragment(F);

+ if (!IsDwarfSec && CsectProp->MappingClass ==XCOFF::XMC_PR){
+    QualName->setFragment(F);
+    QualName->setOffset(0);
+  }

not sure whether it work or not.

[DiggerLin]

llvm/lib/MC/MCContext.cpp

833

sorry that symbol offset is default by 0 . So we do not need to do

QualName->setOffset(0);

[DiggerLin]

llvm/test/CodeGen/PowerPC/aix-xcoff-funcsect.ll

8

do we want to test the 32bit too ?

[Esme]

Addressed comments.
Thx @DiggerLin

[DiggerLin]

LGTM, please wait for several days and Hubert maybe has comment on it. I do not think we need to check so many symbol items and relocation items in the test case, but I can not give any suggestion on it.

llvm/test/CodeGen/PowerPC/aix-xcoff-funcsect.ll

15

nit: change %t64.o

16

nit: change %t64.o

[hubert.reinterpretcast]

llvm/lib/MC/MCContext.cpp

831

The change looks reasonable, but I don't think it should be restricted to XMC_PR csects.

If we are being conservative about making changes, then let's leave a comment to say that the check for XMC_PR is here just because we don't have other cases that hit this problem yet.

We will probably find more to do if we can get the assembly parsing to resolve qualnames.

llvm/test/CodeGen/PowerPC/aix-xcoff-funcsect.ll

11

Please use --symbol-description and update the checks to expect the storage mapping class.

16

Same comment: Please use --symbol-description and update the checks to expect the storage mapping class.

[Esme]

Addressed comments.
Thx @hubert.reinterpretcast and @DiggerLin

[hubert.reinterpretcast]

In D137230#3924110, @Esme wrote:

Addressed comments.

Thanks. Can you update the title and description?

The title should indicate "what" (set fragment). The description can further explain the "why".

[hubert.reinterpretcast]

I am a bit torn over not actually checking that the calculated function sizes are correct, but I guess that we can infer from there being no relocations generated for it that we are going through the right MCExpr processing.

[hubert.reinterpretcast]

LGTM; no objection if we're planning to move ahead without checking the calculated size field in the traceback table.

llvm/lib/MC/MCContext.cpp

MCSectionXCOFF *MCContext::getXCOFFSection(
 
   auto *F = new MCDataFragment();
   Result->getFragmentList().insert(Result->begin(), F);
   F->setParent(Result);
 
   if (Begin)
     Begin->setFragment(F);
 
+  if (!IsDwarfSec && CsectProp->MappingClass == XCOFF::XMC_PR) {
+    QualName->setFragment(F);
+    QualName->setOffset(0);
+  }
+
   return Result;
 }
 
 MCSectionSPIRV *MCContext::getSPIRVSection() {
   MCSymbol *Begin = nullptr;
   MCSectionSPIRV *Result = new (SPIRVAllocator.Allocate())
       MCSectionSPIRV(SectionKind::getText(), Begin);
 

llvm/test/CodeGen/PowerPC/aix-xcoff-funcsect.ll

 ; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -mcpu=pwr4 \
 ; RUN:     -mattr=-altivec -function-sections < %s | \
 ; RUN:   FileCheck --check-prefix=ASM %s
 ; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr4 \
 ; RUN:     -mattr=-altivec -function-sections < %s | \
 ; RUN:   FileCheck --check-prefix=ASM %s
 
+; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=-altivec -function-sections -xcoff-traceback-table=true \
+; RUN:     -filetype=obj -o %t.o < %s
+; RUN: llvm-objdump --syms --reloc %t.o | FileCheck --check-prefix=XCOFF %s
+
 @alias_foo = alias void (...), bitcast (void ()* @foo to void (...)*)
 
 define void @foo() {
 entry:
   ret void
 }
 
 define hidden void @hidden_foo() {
 entry:
   ret void
 }
 

 ; ASM-NEXT:   .vbyte  {{[0-9]+}}, 0
 ; ASM-NEXT:   .csect .static_overalign_foo[PR],6
 ; ASM-NEXT:  # %bb.0:                                # %entry
 ; ASM-NEXT:   blr
 ; ASM:        .extern .extern_foo
 ; ASM-NEXT:   .extern extern_foo[DS]
 ; ASM-NEXT:   .globl  alias_foo
 ; ASM-NEXT:   .globl  .alias_foo
+
+; XCOFF:      SYMBOL TABLE:
+; XCOFF-NEXT: 0000000000000000      df *DEBUG*  0000000000000000 <stdin>
+; XCOFF-NEXT: 0000000000000000         *UND*  0000000000000000 .extern_foo
+; XCOFF-NEXT: 0000000000000000         *UND*  0000000000000000 extern_foo
+; XCOFF-NEXT: 0000000000000000 l       .text  0000000000000000 .text
+; XCOFF-NEXT: 0000000000000000 g       .text  0000000000000019 .foo
+; XCOFF-NEXT: 0000000000000000 g     F .text (csect: .foo)  0000000000000000 .alias_foo
+; XCOFF-NEXT: 0000000000000020 g       .text  0000000000000020 .hidden .hidden_foo
+; XCOFF-NEXT: 0000000000000040 g       .text  0000000000000059 .bar
+; XCOFF-NEXT: 00000000000000c0 l       .text  000000000000002a .static_overalign_foo
+; XCOFF-NEXT: 00000000000000f0 g     O .data  0000000000000018 foo
+; XCOFF-NEXT: 00000000000000f0 g     O .data (csect: foo)   0000000000000000 alias_foo
+; XCOFF-NEXT: 0000000000000108 g     O .data  0000000000000018 .hidden hidden_foo
+; XCOFF-NEXT: 0000000000000120 g     O .data  0000000000000018 bar
+; XCOFF-NEXT: 0000000000000138 l     O .data  0000000000000018 static_overalign_foo
+; XCOFF-NEXT: 0000000000000150 l       .data  0000000000000000 TOC
+
+; XCOFF:      RELOCATION RECORDS FOR [.text]:
+; XCOFF-NEXT: OFFSET           TYPE                     VALUE
+; XCOFF-NEXT: 000000000000004c R_RBR                    .foo
+; XCOFF-NEXT: 0000000000000054 R_RBR                    .static_overalign_foo
+; XCOFF-NEXT: 000000000000005c R_RBR                    .alias_foo
+; XCOFF-NEXT: 0000000000000064 R_RBR                    .extern_foo
+; XCOFF-NEXT: 000000000000006c R_RBR                    .hidden_foo
+; XCOFF:      RELOCATION RECORDS FOR [.data]:
+; XCOFF-NEXT: OFFSET           TYPE                     VALUE
+; XCOFF-NEXT: 0000000000000000 R_POS                    .foo
+; XCOFF-NEXT: 0000000000000008 R_POS                    TOC
+; XCOFF-NEXT: 0000000000000018 R_POS                    .hidden_foo
+; XCOFF-NEXT: 0000000000000020 R_POS                    TOC
+; XCOFF-NEXT: 0000000000000030 R_POS                    .bar
+; XCOFF-NEXT: 0000000000000038 R_POS                    TOC
+; XCOFF-NEXT: 0000000000000048 R_POS                    .static_overalign_foo
+; XCOFF-NEXT: 0000000000000050 R_POS                    TOC