Add -{no,}-check-sections flag to enable/disable section overlap checking.

[ruiu]

Summary

GNU linkers have this option. Fixes https://bugs.llvm.org/show_bug.cgi?id=36205

[ruiu]

• Rebase

[smeenai]

LGTM with the inline comment.

lld/ELF/Options.td

35–36

Should these say "section" instead of "segment"?

[jhenderson]

I think the test needs extending to include the "no warning printed" behaviour, specific to --no-check-sections.

[smeenai]

In D42858#997516, @jhenderson wrote:

I think the test needs extending to include the "no warning printed" behaviour, specific to --no-check-sections.

It's an error, not a warning, so just checking for the link to succeed should be enough, right?

[jhenderson]

Yes, but this switch shouldn't behave the same as --noinhibit-exec, which produces a warning, hence why I think it's worthwhile testing.

lld/ELF/Config.h

struct Configuration {
   bool AllowMultipleDefinition;
   bool AndroidPackDynRelocs = false;
   bool ARMHasBlx = false;
   bool ARMHasMovtMovw = false;
   bool ARMJ1J2BranchEncoding = false;
   bool AsNeeded = false;
   bool Bsymbolic;
   bool BsymbolicFunctions;
+  bool CheckSections;
   bool CompressDebugSections;
   bool DefineCommon;
   bool Demangle = true;
   bool DisableVerify;
   bool EhFrameHdr;
   bool EmitRelocs;
   bool EnableNewDtags;
   bool ExportDynamic;

lld/ELF/Driver.cpp

 
 // Initializes Config members by the command line options.
 void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->AllowMultipleDefinition =
       Args.hasArg(OPT_allow_multiple_definition) || hasZOption(Args, "muldefs");
   Config->AuxiliaryList = args::getStrings(Args, OPT_auxiliary);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
+  Config->CheckSections =
+      Args.hasFlag(OPT_check_sections, OPT_no_check_sections, true);
   Config->Chroot = Args.getLastArgValue(OPT_chroot);
   Config->CompressDebugSections = getCompressDebugSections(Args);
   Config->DefineCommon = Args.hasFlag(OPT_define_common, OPT_no_define_common,
                                       !Args.hasArg(OPT_relocatable));
   Config->Demangle = Args.hasFlag(OPT_demangle, OPT_no_demangle, true);
   Config->DisableVerify = Args.hasArg(OPT_disable_verify);
   Config->Discard = getDiscard(Args);
   Config->DynamicLinker = getDynamicLinker(Args);

lld/ELF/Options.td

 def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
 
 def build_id: F<"build-id">, HelpText<"Generate build ID note">;
 
 def build_id_eq: J<"build-id=">, HelpText<"Generate build ID note">;
 
+defm check_sections : B<"check-sections",
+    "Check segment addresses for overlaps",
+    "Do not check segment addresses for overlaps">;
+
 defm compress_debug_sections : Eq<"compress-debug-sections">,
   HelpText<"Compress DWARF debug sections">;
 
 defm defsym: Eq<"defsym">, HelpText<"Define a symbol alias">;
 
 defm library_path: Eq<"library-path">,
   HelpText<"Add a directory to the library search path">, MetaVarName<"<dir>">;
 

lld/ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::run() {
 
   setPhdrs();
 
   if (Config->Relocatable) {
     for (OutputSection *Sec : OutputSections)
       Sec->Addr = 0;
   }
 
+  if (Config->CheckSections)
     checkNoOverlappingSections();
 
   // It does not make sense try to open the file if we have error already.
   if (errorCount())
     return;
   // Write the result down to a file.
   openFile();
   if (errorCount())
     return;

lld/test/ELF/linkerscript/overlapping-sections.s

 # RUN:   .sec1 0x8000 : AT(0x8000) { sec1_start = .; *(.first_sec) sec1_end = .;} \
 # RUN:   .sec2 0x8800 : AT(0x8080) { sec2_start = .; *(.second_sec) sec2_end = .;} \
 # RUN: }" > %t-lma.script
 # RUN: not ld.lld -o %t.so --script %t-lma.script %t.o -shared 2>&1 | FileCheck %s -check-prefix LMA-OVERLAP-ERR
 # LMA-OVERLAP-ERR:      error: section .sec1 load address range overlaps with .sec2
 # LMA-OVERLAP-ERR-NEXT: >>> .sec1 range is [0x8000 -> 0x80FF]
 # LMA-OVERLAP-ERR-NEXT: >>> .sec2 range is [0x8080 -> 0x817F]
 
-# check that we create the expected binary with --noinhibit-exec:
+# Check that we create the expected binary with --noinhibit-exec or --no-check-sections:
 # RUN: ld.lld -o %t.so --script %t-lma.script %t.o -shared --noinhibit-exec
+# RUN: ld.lld -o %t.so --script %t-lma.script %t.o -shared --no-check-sections
+# RUN: ld.lld -o %t.so --script %t-lma.script %t.o -shared --check-sections --no-check-sections
 
 # Verify that the .sec2 was indeed placed in a PT_LOAD where the PhysAddr
 # overlaps with where .sec1 is loaded:
 # RUN: llvm-readobj -sections -program-headers -elf-output-style=GNU %t.so | FileCheck %s -check-prefix BAD-LMA
 # BAD-LMA-LABEL: Section Headers:
 # BAD-LMA: .sec1             PROGBITS        0000000000008000 018000 000100 00  WA  0   0  1
 # BAD-LMA: .sec2             PROGBITS        0000000000008800 018800 000100 00  WA  0   0  1
 # BAD-LMA-LABEL: Program Headers: