[ft-devel] strict aliasing

[Ken Turkowski]

Compilers are beginning to embrace more aggressive optimization techniques. One 
of these directions is that of strict aliasing. We have experienced crashes on 
some ARM embedded devices in some code that was flagged with the “strict 
aliasing” warning. We have been going through our code, changing casts to 
unions in appropriate ways, and have sidestepped the crashes.

However, Freetype is a bit of a problem, since it is open source.

Are you planning to make a pass over the Freetype code base to eradicate these 
strict aliases?

The following warnings were produced by the Android NDK R10e compiler, which is 
currently the chattiest:

/freetype-2.6/include/config/ftmodule.h:14:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:15:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:16:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:17:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:18:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:19:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:20:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:21:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:25:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:27:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:28:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:29:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/include/config/ftmodule.h:30:1: warning: dereferencing 
type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/autofit/afcjk.c:161:7: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/autofit/aflatin.c:155:7: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cache/ftcbasic.c:264:3: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cache/ftcbasic.c:321:5: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cache/ftcbasic.c:388:5: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cache/ftcbasic.c:447:3: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cache/ftcbasic.c:504:5: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cache/ftcbasic.c:573:5: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/cff/cf2font.c:474:31: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/sfnt/ttcmap.c:3534:13: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/sfnt/ttcmap.c:3539:13: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]
/freetype-2.6/src/sfnt/ttcmap.c:3542:15: warning: dereferencing type-punned 
pointer might break strict-aliasing rules [-Wstrict-aliasing]

For more helpful information, do “man gcc” and search for ‘-fstrict-aliasing:.

Ken Turkowski
Marvell Semiconductor