pkg/55843: multimeda/ffmpeg4: SIGSEGV on ebml_parse and other routines on i386

[jbryn%students.wcpss.net@localhost]

>Number:         55843
>Category:       pkg
>Synopsis:       multimeda/ffmpeg4: SIGSEGV on ebml_parse and other routines on i386
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 05 08:35:00 +0000 2020
>Originator:     Jackson Bryn
>Release:        NetBSD-current 9.99.76, pkgsrc/current 12/5/20
>Organization:
N/A
>Environment:
build.localdomain 9.99.76 NetBSD 9.99.76 (GENERIC) #0: Mon Nov 30 07:53:42 UTC 2020  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/i386/compile/GENERIC i386
>Description:
Tested on a Haswell in 32-bit mode.
Unsure what the exact situation is, but if I blank my CLFAGS additions to nothing but -pipe -fomit-frame-pointer, it works again.

Faulty CFLAGS additions:
CFLAGS += -O2 -pipe -march=bonnell -mtune=bonnell -mfpmath=sse -fomit-frame-pointer
Working CFLAGS additions:
CFLAGS += -pipe -fomit-frame-pointer

(Commenting out --disable-optimizations also seems to have no negative effects, by the way.)
>How-To-Repeat:
A simple method to reproduce is to copy a mp4 and an m4a to a matroska file.
>Fix:
It's best that we probably have ffmpeg4 override CFLAGS and optimizations on i386. I'm not sure if it happens on other arches.