[ELF] Add --no-warnings/-w

[MaskRay]

Summary

Mach-O ld64 supports -w to suppress warnings. GNU ld 2.40 will support the
option as well (https://sourceware.org/bugzilla/show_bug.cgi?id=29654).

This feature has some small value. E.g. when analyzing a large executable with
relocation overflow issues, we may use --noinhibit-exec --emit-relocs to get
relocations and an output file despite relocation overflow issues. -w can significantly
improve the link time as printing the massive warnings is slow.

[peter.smith]

I think it makes sense as the first level of warning control and matching the GNU ld featureset is useful.

One thing we may want to do in the future is have named individual warnings like clang that can be individually suppressed. I've found that useful in Arm's proprietary linker as customers sometimes find a single warning annoying, but don't want to turn of all warnings. This is a lot more effort to implement and maintain though.

[MaskRay]

Thanks for the quick review!

lld/ELF/Driver.cpp

 
 void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   ELFOptTable parser;
   opt::InputArgList args = parser.parse(argsArr.slice(1));
 
   // Interpret these flags early because error()/warn() depend on them.
   errorHandler().errorLimit = args::getInteger(args, OPT_error_limit, 20);
   errorHandler().fatalWarnings =
-      args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
+      args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false) &&
+      !args.hasArg(OPT_no_warnings);
+  errorHandler().suppressWarnings = args.hasArg(OPT_no_warnings);
   checkZOptions(args);
 
   // Handle -help
   if (args.hasArg(OPT_help)) {
     printHelp();
     return;
   }
 

lld/ELF/Options.td

def no_nmagic: F<"no-nmagic">, MetaVarName<"<magic>">,
   HelpText<"Page align sections (default)">;
 
 def no_omagic: F<"no-omagic">, MetaVarName<"<magic>">,
   HelpText<"Do not set the text data sections to be writable, page align sections (default)">;
 
 def no_undefined: F<"no-undefined">,
   HelpText<"Report unresolved symbols even if the linker is creating a shared library">;
 
+def no_warnings: FF<"no-warnings">, HelpText<"Suppress warnings and cancel --fatal-warnings">;
+def : Flag<["-"], "w">, Alias<no_warnings>, HelpText<"Alias for --no-warnings">;
+
 def o: JoinedOrSeparate<["-"], "o">, MetaVarName<"<path>">,
   HelpText<"Path to file to write output">;
 
 defm oformat: EEq<"oformat", "Specify the binary format for the output object file">,
   MetaVarName<"[elf,binary]">;
 
 def omagic: FF<"omagic">, MetaVarName<"<magic>">,
   HelpText<"Set the text and data sections to be readable and writable, do not page align sections, link against static libraries">;

lld/docs/ReleaseNotes.rst

 ELF Improvements
 ----------------
 
 * ``ELFCOMPRESS_ZSTD`` compressed input sections are now supported.
   (`D129406 <https://reviews.llvm.org/D129406>`_)
 * ``--compress-debug-sections=zstd`` is now available to compress debug
   sections with zstd (``ELFCOMPRESS_ZSTD``).
   (`D133548 <https://reviews.llvm.org/D133548>`_)
+* ``--no-warnings``/``-w`` is now available to suppress warnings.
+  (`D136569 <https://reviews.llvm.org/D136569>`_)
 
 Breaking changes
 ----------------
 
 COFF Improvements
 -----------------
 
 * ...

lld/docs/ld.lld.1

 .It Fl -no-rosegment
 Do not put read-only non-executable sections in their own segment.
 .It Fl -no-undefined-version
 Report version scripts that refer undefined symbols.
 .It Fl -no-undefined
 Report unresolved symbols even if the linker is creating a shared library.
 .It Fl -no-warn-symbol-ordering
 Do not warn about problems with the symbol ordering file or call graph profile.
+.It Fl -no-warnings , Fl w
+Suppress warnings and cancel
+.Cm --fatal-warnings.
 .It Fl -no-whole-archive
 Restores the default behavior of loading archive members.
 .It Fl -no-pie , Fl -no-pic-executable
 Do not create a position independent executable.
 .It Fl -noinhibit-exec
 Retain the executable output file whenever it is still usable.
 .It Fl -nostdlib
 Only search directories specified on the command line.

lld/test/ELF/no-inhibit-exec.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: not ld.lld %t -o /dev/null
 # RUN: ld.lld %t --noinhibit-exec -o %t2
 # RUN: llvm-objdump -d %t2 | FileCheck %s
 # RUN: llvm-readobj -r %t2 | FileCheck %s --check-prefix=RELOC
 
+# RUN: ld.lld %t -w --noinhibit-exec -o /dev/null 2>&1 | count 0
+
 # CHECK: Disassembly of section .text:
 # CHECK-EMPTY:
 # CHECK-NEXT: _start
 # CHECK-NEXT: 201120: {{.*}} callq 0x0
 
 # RELOC:      Relocations [
 # RELOC-NEXT: ]
 
 # next code will not link without noinhibit-exec flag
 # because of undefined symbol _bar
 .globl _start
 _start:
   call _bar

lld/test/ELF/warnings.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t1.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/warn-common.s -o %t2.o
 
 # RUN: ld.lld --warn-common %t1.o %t2.o -o /dev/null 2>&1 | \
 # RUN:   FileCheck -check-prefix=ERR %s
 # ERR: multiple common of
 
 # RUN: not ld.lld --warn-common --fatal-warnings %t1.o %t2.o -o /dev/null 2>&1 | \
 # RUN:   FileCheck -check-prefix=ERR %s
 
+## --no-warnings/-w suppresses warnings and cancel --fatal-warnings.
+# RUN: ld.lld --no-warnings --warn-common %t1.o %t2.o -o /dev/null 2>&1 | count 0
+# RUN: ld.lld -w --fatal-warnings --warn-common %t1.o %t2.o -o /dev/null 2>&1 | count 0
+
 .globl _start
 _start:
 
 .type arr,@object
 .comm arr,4,4