[XCOFF][AIX] report_fatal_error when an overflow section is needed

[jasonliu]

Summary

If there are more than 65534 relocation entries in a single section, we should generate an overflow section.
Since we don't support overflow section for now, we should generate an error.

[DiggerLin]

why the file llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll so large ,it can not be loaded?

[jasonliu]

In D81104#2072208, @DiggerLin wrote:

why the file llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll so large ,it can not be loaded?

I was able to load it by clicking Show File Contents.
I'm open to any ideas that could greatly reduce the file size and still trigger the error I put in.

[daltenty]

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

7

We're able to sed and friends in tests, so I think we can do an expansion based on @hubert.reinterpretcast original preprocessor example. Replacing the repeated line with 'A' and using something like this seems like it would do the trick:

sed "s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;s/A/ABA/g;" %s| tr B "\n" | sed "s/A/call\ void\ bitcast\ \(void (...)*\ @foo\ to\ void\ ()*)()/g"|llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o

[jasonliu]

Use sed to generate the test.

[jasonliu]

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

7

Thanks for the suggestion.
I could not 'sed' the same file that the 'sed' command resides. So I created an input file instead.

[hubert.reinterpretcast]

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

7

Would grep -v have helped there?

[jasonliu]

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

7

Hmm... I'm not sure how grep -v would help.
The problem I'm seeing is:
when this file get passed into the sed command, sed command would replace the A recursively inside this sed command, which would result in an output file like:

;; This test generates more than 65535 relocation entries in a single section,
;; which would trigger an overflow section to be generated in 32-bit mode.
;; Since overflow section is not supported yet, we will emit an error instead of
;; generating an invalid binary for now.

; RUN: sed "s/call void bitcast (void (...)* @foo to void ()*)()
call void bitcast (void (...)* @foo to void ()*)()
call void bitcast (void (...)* @foo to void ()*)()
call void bitcast (void (...)* @foo to void ()*)()
.... 
/g;" \
; RUN:     %p/Inputs/reloc-sed.ll | tr B "\n" | \
....

[jasonliu]

Remove input files and use grep -v

[hubert.reinterpretcast]

llvm/lib/MC/XCOFFObjectWriter.cpp

744

Semantically, this is not UINT16_MAX but an XCOFF-defined constant. Otherwise, the maximum representable value would be UINT16_MAX itself and not one less. RelocOverflow is currently defined in lib/Object/XCOFFObjectFile.cpp, but it should probably be defined in include/llvm/BinaryFormat/XCOFF.h.

750

Move the check to before the addition; use: Section->RelocationCount >= UINT16_MAX - Csect.Relocations.size(). After said move, the two if statements can be merged.

[hubert.reinterpretcast]

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

8

I suggest testing exactly 65535:

; RUN: grep -v RUN: %s | \
; RUN:   sed >%t.overflow.ll 's/SIZE/65535/;s/MACRO/#/;s/#/################/g;s/#/################/g;s/#/################/g;s/#/################/g;s/#/#_/g;s/_#_\([^#]\)/\1/;s/_/, /g;s/#/i8* @c/g;'
; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff \
; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.overflow.ll 2>&1 | \
; RUN:   FileCheck --check-prefix=XCOFF32 %s
; XCOFF32: LLVM ERROR: relocation entries overflowed; overflow section is not implemented yet

; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff \
; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.overflow.ll 2>&1 | \
; RUN:   FileCheck --check-prefix=XCOFF64 %s
; XCOFF64: LLVM ERROR: 64-bit XCOFF object files are not supported yet.

@c = external global i8, align 1
@arr = global [SIZE x i8*] [MACRO], align 8

Also, I think we should test for 65534.

[jasonliu]

Address Hubert's comment.

[jasonliu]

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

8

Thanks. I was pleasantly surprised that the suggested test(4 llc invocation) finished within 30 seconds.

[daltenty]

LGTM

llvm/lib/MC/XCOFFObjectWriter.cpp

754

nit: Capitalization and period.

[jasonliu]

llvm/lib/MC/XCOFFObjectWriter.cpp

754

https://llvm.org/docs/CodingStandards.html#error-and-warning-messages
ask us not to capitalize first letter and end with period.

[hubert.reinterpretcast]

LGTM with minor comments.

llvm/test/CodeGen/PowerPC/aix-xcoff-huge-relocs.ll

8 ↗

(On Diff #268823)

Minor nit: Not sure if we want to align -mcpu with the llc options?

21 ↗

(On Diff #268823)

Same comment.

24 ↗

(On Diff #268823)

Same comment.

31 ↗

(On Diff #268823)

I think we'd need the NOT lines after the other lines as well.

llvm/lib/MC/XCOFFObjectWriter.cpp

for (auto *Section : Sections) {
     if (Section->Index == Section::UninitializedIndex)
       // Nothing to record for this Section.
       continue;
 
     for (const auto *Group : Section->Groups) {
       if (Group->empty())
         continue;
 
-      for (auto &Csect : *Group)
+      for (auto &Csect : *Group) {
+        if (Csect.Relocations.size() >= UINT16_MAX)
+          report_fatal_error(
+              "relocation entries overflowed; overflow section is "
+              "not implemented yet");
+
         Section->RelocationCount += Csect.Relocations.size();
+        if (Section->RelocationCount >= UINT16_MAX)
+          report_fatal_error(
+              "relocation entries overflowed; overflow section is "
+              "not implemented yet");
+      }
     }
   }
 
   // Calculate the file offset to the relocation entries.
   uint64_t RawPointer = RelocationEntryOffset;
   for (auto Sec : Sections) {
     if (Sec->Index == Section::UninitializedIndex || !Sec->RelocationCount)
       continue;

llvm/test/CodeGen/PowerPC/Inputs/reloc-sed.ll

+define void @bar() {
+entry:
+;; We would replace the line below in ../aix-xcoff-reloc-overflow.ll
+A
+  ret void
+}
+
+declare void @foo(...)

llvm/test/CodeGen/PowerPC/aix-xcoff-reloc-overflow.ll

+;; This test generates more than 65535 relocation entries in a single section,
+;; which would trigger an overflow section to be generated in 32-bit mode.
+;; Since overflow section is not supported yet, we will emit an error instead of
+;; generating an invalid binary for now.
+
+; RUN: sed "s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABABA/g;s/A/ABA/g;s/A/ABA/g;" \
+; RUN:     %p/Inputs/reloc-sed.ll | tr B "\n" | \
+; RUN:   sed "s/A/call\ void\ bitcast\ \(void (...)*\ @foo\ to\ void\ ()*)()/g" > %t.ll
+
+; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff \
+; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.ll 2>&1 | \
+; RUN:   FileCheck --check-prefix=XCOFF32 %s
+; XCOFF32: LLVM ERROR: relocation entries overflowed; overflow section is not implemented yet
+
+; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff \
+; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.ll 2>&1 | \
+; RUN:   FileCheck --check-prefix=XCOFF64 %s
+; XCOFF64: LLVM ERROR: 64-bit XCOFF object files are not supported yet.