[COFF] Check for sections larger than 4 GiB

[smeenai]

Summary

Sections are limited to 4 GiB. Error out early if a section exceeds this
size, rather than overflowing the section size and getting confusing
assertion failures/segfaults later.

[smeenai]

I'm not sure how to write a test case for this without creating an object file with a section > 4 GiB (as in that object file will take upwards of 4 GiB on disk). Any ideas?

[ruiu]

How about creating huge .bss sections and link them?

[smeenai]

In D38005#874414, @ruiu wrote:

How about creating huge .bss sections and link them?

Do you mean using yaml2obj? I don't know of a way to do that via assembler directives (and I'd love to learn if there is one).

[davide]

yaml2obj should allow you to create a broken object like that. IIRC there's an example in test/ELF.

[ruiu]

I believe there's a way to create a huge .bss section using assembler, but yaml2obj is fine. We are using it for COFF tests (but not for ELF tests.)

[ruiu]

COFF/Writer.cpp

191

Can you use errro() instead? We use fatal() only for reporting corrupted input files. Files with too large sections are not technically corrupted.

[smeenai]

Change to error and add test.

[smeenai]

Exit with correct error code.

[ruiu]

LGTM

test/COFF/section-size.s

3–5

It seems just %t1.obj and %t3.obj suffice.

9

Instead of creating a temporary file by cp, you can just pass the same object file twice.

[smeenai]

test/COFF/section-size.s

3–5

Sure, will rename.

9

lld-link deduplicates input object files: https://reviews.llvm.org/diffusion/L/browse/lld/trunk/COFF/Driver.cpp;313693$295-303. Is there some other way to get around that?

[ruiu]

test/COFF/section-size.s

9

Oh, I didn't know that. cp is of course fine if that's the case.

COFF/Driver.cpp

void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
 
   // Identify identical COMDAT sections to merge them.
   if (Config->DoICF)
     doICF(Symtab->getChunks());
 
   // Write the result.
   writeResult();
 
+  if (ErrorCount)
+    return;
+
   // Call exit to avoid calling destructors.
   exit(0);
 }
 
 } // namespace coff
 } // namespace lld

COFF/Writer.cpp

 void OutputSection::addChunk(Chunk *C) {
   Chunks.push_back(C);
   C->setOutputSection(this);
   uint64_t Off = Header.VirtualSize;
   Off = alignTo(Off, C->Alignment);
   C->setRVA(Off);
   C->OutputSectionOff = Off;
   Off += C->getSize();
+  if (Off > UINT32_MAX)
+    error("section larger than 4 GiB: " + Name);
   Header.VirtualSize = Off;
   if (C->hasData())
     Header.SizeOfRawData = alignTo(Off, SectorSize);
 }
 
 void OutputSection::addPermissions(uint32_t C) {
   Header.Characteristics |= C & PermMask;
 }

test/COFF/section-size.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc %s -o %tmain.obj
+# RUN: echo '.lcomm s, 0x80000000' | llvm-mc -filetype=obj -triple=x86_64-windows-msvc -o %t80000000_1.obj
+# RUN: cp %t80000000_1.obj %t80000000_2.obj
+# RUN: echo '.lcomm s, 0xffffffff' | llvm-mc -filetype=obj -triple=x86_64-windows-msvc -o %tffffffff.obj
+
+# Run: lld-link -entry:main %tmain.obj %tffffffff.obj -out:%t.exe
+
+# RUN: not lld-link -entry:main %tmain.obj %t80000000_1.obj %t80000000_2.obj -out:%t.exe 2>&1 | FileCheck %s
+# CHECK: error: section larger than 4 GiB: .bss
+
+.globl main
+main:
+  retq