First stab at UPDATING notes for clang 3.5.0.

This commit is contained in:
Dimitry Andric 2014-12-30 22:46:20 +00:00
parent 3ed527f1b5
commit 143c11b4d1

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@ -31,6 +31,62 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 11.x IS SLOW:
disable the most expensive debugging functionality run
"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
20141231:
Clang, llvm and lldb have been upgraded to 3.5.0 release.
As of this release, a prerequisite for building llvm and clang is a
C++11 capable compiler and C++11 standard library. This means that to
be able to successfully build the cross-tools stage of buildworld, with
clang as the bootstrap compiler, your system compiler or cross compiler
should either be clang 3.3 or later, or gcc 4.8 or later, and your
system C++ library should be libc++, or libdstdc++ from gcc 4.8 or
later.
On any earlier standard FreeBSD 10.x or 11.x installation, where clang
and libc++ are on by default (that is, on x86 or arm), this should work
out of the box, unless you explicitly disabled clang or libc++. In that
case, you must re-enable, build and install both of those first.
On 9.x installations where clang is enabled by default, e.g. on x86 and
powerpc, libc++ will not be enabled by default, so libc++ should be
built (with clang) and installed first. If both clang and libc++ are
missing, build clang first, then use it to build libc++.
On 8.x and earlier installations, upgrade to 9.x first, and then follow
the instructions for 9.x above.
This new version of clang introduces a number of new warnings, of which
the following are most likely to appear:
-Wabsolute-value
This warns in two cases, for both C and C++:
* When the code is trying to take the absolute value of an unsigned
quantity, which is effectively a no-op, and almost never what was
intended. The code should be fixed, if at all possible. If you are
sure that the unsigned quantity can be safely cast to signed, without
loss of information or undefined behavior, you can add an explicit
cast, or disable the warning.
* When the code is trying to take an absolute value, but the called
abs() variant is for the wrong type, which can lead to truncation.
If you want to disable the warning instead of fixing the code, please
make sure that truncation will not occur, or it might lead to unwanted
side-effects.
-Wtautological-undefined-compare and
-Wundefined-bool-conversion
These warn when C++ code is trying to compare 'this' against NULL, while
'this' should never be NULL in well-defined C++ code. However, there is
some legacy (pre C++11) code out there, which actively abuses this
feature, which was less strictly defined in previous C++ versions.
Squid and openjdk do this, for example. The warning can be turned off
for C++98 and earlier, but compiling the code in C++11 mode might result
in unexpected behavior; for example, the parts of the program that are
unreachable could be optimized away.
20141222:
The old NFS client and server (kernel options NFSCLIENT, NFSSERVER)
kernel sources have been removed. The .h files remain, since some