Re: clang build buggy code with certain CPUTYPE setting

On 26 Sep 2020, at 13:40, Marek Zarychta <zarychtam_at_plan-b.pwste.edu.pl> wrote:
> 
> I have done a few builds of CURRENT in a row one or two weeks apart. The
> builds with CPUTYPE?=amdfam10 set produce buggy code, for example while
> running mergemaster I get this error:
> 
> PLEASE submit a bug report to https://bugs.freebsd.org/submit/ and
> include the crash backtrace, preprocessed source, and associated run
> script.
> Stack dump:
> 0.      Program arguments: cc --version
> #0 0x00000000040ede6e (/usr/bin/cc+0x40ede6e)
> #1 0x00000000040ec0e5 (/usr/bin/cc+0x40ec0e5)
> #2 0x00000000040ee550 (/usr/bin/cc+0x40ee550)
> #3 0x000000080553babe (/lib/libthr.so.3+0x19abe)
> Illegal instruction
> make: "/usr/src/share/mk/bsd.compiler.mk" line 181: Unable to determine
> compiler type for CC=cc.  Consider setting COMPILER_TYPE.
> 
> The 13-CURRENT world built without CPUTYPE runs fine, the same for
> recent 12.2-STABLE world build with CPUTYPE?=amdfam10 on the same
> machine.

Hi Marek,

In r365507 (on 2020-09-09) I committed a fix for amdfam10:

------------------------------------------------------------------------
r365507 | dim | 2020-09-09 20:11:04 +0200 (Wed, 09 Sep 2020) | 17 lines

Merge commit e6bb4c8e7 from llvm git (by Craig Topper):

  [X86] SSE4_A should only imply SSE3 not SSSE3 in the frontend.

  SSE4_1 and SSE4_2 due imply SSSE3. So I guess I got confused when
  switching the code to being table based in D83273.

  Fixes PR47464

This should fix builds with -march=amdfam10 emitting SSSE3 instructions
such as pshufb, which lead to programs crashing with SIGILL on such
processors.

Reported by:    avg
MFC after:      6 weeks
X-MFC-With:     r364284

So I expect that the "Illegal instruction" you are seeing is an SSSE3
instruction. If this happens with your base compiler, please get a
known-good copy from one of the snapshot images. Ensure your /usr/src is
r365507 or later, then do a full buildworld and reinstall.

-Dimitry