Disable assembler warning “.section __TEXT,__textc

When using MacPorts GCC on OS X and enlisting the Clang Integrated Assembler via -Wa,-q, the assembler produces a stream of warnings for each file. A sampling of the warnings is shown below (so many of them, the Stack Overflow editor would not allow me to paste the entire stream).

I found LLVM Commit r250349, Stop generating coal sections. Here's the code responsible, but its not clear to me how to disable the warning.

+  // Issue a warning if the target is not powerpc and Section is a *coal* section.
+  Triple TT = getParser().getContext().getObjectFileInfo()->getTargetTriple();
+  Triple::ArchType ArchTy = TT.getArch();
+
+  if (ArchTy != Triple::ppc && ArchTy != Triple::ppc64) {
+    StringRef NonCoalSection = StringSwitch<StringRef>(Section)
+                                   .Case("__textcoal_nt", "__text")
+                                   .Case("__const_coal", "__const")
+                                   .Case("__datacoal_nt", "__data")
+                                   .Default(Section);
+
+    if (!Section.equals(NonCoalSection)) {
+      StringRef SectionVal(Loc.getPointer());
+      size_t B = SectionVal.find(',') + 1, E = SectionVal.find(',', B);
+      SMLoc BLoc = SMLoc::getFromPointer(SectionVal.data() + B);
+      SMLoc ELoc = SMLoc::getFromPointer(SectionVal.data() + E);
+      getParser().Warning(Loc, "section \"" + Section + "\" is deprecated",
+                          SMRange(BLoc, ELoc));
+      getParser().Note(Loc, "change section name to \"" + NonCoalSection +
+                       "\"", SMRange(BLoc, ELoc));
+    }
+  }
+

I can't redirect 2 > /dev/null because the configuration is a bit fragile at the moment, and it discards other warnings and errors.

How do I disable the Clang assembler warning on coal sections?

When the GCC compiler encounters -Wa,-q, it uses /opt/local/bin/clang as the assembler rather than /opt/local/bin/as. Here are the relevant versions.

$ /opt/local/bin/g++-mp-6 --version
g++-mp-6 (MacPorts gcc6 6.1.0_0) 6.1.0
Copyright (C) 2016 Free Software Foundation, Inc.

$ /opt/local/bin/clang --version
clang version 3.8.0 (branches/release_38 262722)
Target: x86_64-apple-darwin12.6.0

$ /opt/local/bin/as -version
Apple Inc version cctools-877.8, GNU assembler version 1.38

Adding -Wno-deprecated to CXXFLAGS does not suppress the warning. I also tried -fno-tree-coalesce-vars with no joy (which may hurt performance).

And the following sed does not match on OS X using sed or gsed:

$ CXXFLAGS="-DNDEBUG -g2 -O2" make CXX=/opt/local/bin/g++-mp-6 2>&1 | \
  gsed -e '/(__TEXT|__DATA)/,+2d'
/opt/local/bin/g++-mp-6 -DNDEBUG -g2 -O2 -fPIC -march=native -Wa,-q -pipe -c rijndael.cpp
<stdin>:3:11: warning: section "__textcoal_nt" is deprecated
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:3:11: note: change section name to "__text"
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
...

/opt/local/bin/g++-mp-6 -DNDEBUG -g2 -O2 -fPIC -march=native -Wa,-q -DMACPORTS_GCC_COMPILER=1 -c cryptlib.cpp
<stdin>:3:11: warning: section "__textcoal_nt" is deprecated
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:3:11: note: change section name to "__text"
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:2665:11: warning: section "__textcoal_nt" is deprecated
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:2665:11: note: change section name to "__text"
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:3925:11: warning: section "__textcoal_nt" is deprecated
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:3925:11: note: change section name to "__text"
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:3963:11: warning: section "__textcoal_nt" is deprecated
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~
<stdin>:3963:11: note: change section name to "__text"
        .section __TEXT,__textcoal_nt,coalesced,pure_instructions
                 ^      ~~~~~~~~~~~~~

[Hundred of these ommitted for each source file]

Here are the relevant GCC and LLVM bug reports:

GCC Issue 71767 - Endless stream of warnings when using GCC with -Wa,-q and Clang Integrated Assembler
LLVM Issue 28427 - Endless stream of warnings when using GCC with -Wa,-q and Clang Integrated Assembler

回答1:

At present, you cannot disable those warnings. You should probably file a bug report against FSF GCC to have them update their codegen to be more compliant.

You might also want to file a bug report with llvm.org to request that there be a way to silence these warnings or limit the number that are issued so as to not deluge the user.

回答2:

Apparently there's no way to disable those warnings, but I like your idea of just filtering them out of the build output.

I find sed to be too tricky to bother with for complicated (e.g. multi-line) match/replace patterns. Here's a simple Python program to filter such warning noise from stderr, without hiding stderr entirely.

#!/usr/bin/python
# 
# filter-noisy-assembler-warnings.py
# Author: Stuart Berg

import sys

for line in sys.stdin:
    # If line is a 'noisy' warning, don't print it or the following two lines.
    if ('warning: section' in line and 'is deprecated' in line
    or 'note: change section name to' in line):
        next(sys.stdin)
        next(sys.stdin)
    else:
        sys.stderr.write(line)
        sys.stderr.flush()

A convenient way to use that program is via bash process substitution, applied only to stderr:

$ make 2> >(python filter-noisy-assembler-warnings.py)

Or with your build command, this ought to do the trick, I think:

$ CXXFLAGS="-DNDEBUG -g2 -O2" make CXX=/opt/local/bin/g++-mp-6 2> >(python filter-noisy-assembler-warnings.py)

That way, stdout isn't redirected at all, and most of stderr is written out verbatim, except for those particular annoying warnings.