Hello.

I've been experimenting building GCC with --enable-libstdcxx-debug.

I'm stopping the process after make install (on the function build()), to
better understand what's being built, but there's one thing I'm not sure of
and I wonder if you could help me understand it.

GCC docs say that configuring GCC with --enable-libstdcxx-debug will build
debug libraries "in addition to what is normally built", i.e., in addition
to the optimized libraries.

I've tested this on Linux (Fedora 22, gcc 5.2.0), and it works as expected.
It builds two versions of libstdc++.a and a libstdc++.so
(libstdc++.so.6.0.21), which are installed in
<prefix>/lib/gcc/x86_64-redhat-linux/5.2.0 (optimized version, or "what is
normally built"), and in <prefix>/lib/gcc/x86_64-redhat-linux/5.2.0/debug
(debug version).

However, using --enable-libstdcxx-debug on MSYS2 gives me a different
result. I got a single libstdc++.dll, in <prefix>/bin, and two versions of
libstdc++.a, one in <prefix>/lib/gcc/x86_64-w64-mingw32/5.2.0 and another
in <prefix>/lib/gcc/x86_64-w64-mingw32/5.2.0/debug.

My first hypothesis was that --enable-libstdcxx-debug on MSYS2 was not
creating the debug DLL (which I expected to find in
<prefix>/lib/gcc/x86_64-w64-mingw32/5.2.0/debug). However, when I compared
the versions of libstdc++.dll created using --enable-libstdcxx-debug vs.
--disable-libstdcxx-debug, I noticed they were different.

So, my conclusion, so far, is that --disable-libstdcxx-debug acts similar
on Linux and MSYS2, and that --enable-libstdcxx-debug, on MSYS2, has the
following behaviour:
- Does not create the libstdc++.dll that is "normally built", i.e., the
optimized version.
- Creates the debug version of libstdc++.dll and installs it in
<prefix>/bin.
- Creates the debug version of libstdc++.a and installs it in
<prefix>/lib/gcc/x86_64-w64-mingw32/5.2.0/debug.
- Created the libstdc++.a that is "normally built", i.e., the optimized
version, and installs it in <prefix>lib/gcc/x86_64-w64-mingw32/5.2.0.

Is my reasoning correct, or am I missing something?

Thanks for your help.
---
Paulo Caetano
http://cidebycide.blogspot.pt/
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