Re: Newbie back again...

[Josh Freeman]

On Jun 20, 2017, at 5:30 AM, David Chisnall wrote:

> On 19 Jun 2017, at 23:43, Josh Freeman  
> <address@hidden> wrote:
> >  The segmentation fault happens after Base sets the value of an  
> > NSThread ivar, because the memory location it writes to overlaps  
> > the area in memory where GUI expects to find a different ivar, due  
> > to the mismatched layouts; When GUI reads its ivar, it finds a  
> > nonzero value (garbage), and when the garbage value is sent an objc  
> > message, it crashes.
>
> This sounds like a compiler bug.  The ivar accesses should both be  
> using the same offset variable.  Are you sure that both are being  
> compiled with the same ABI?

   Both Base's & GUI's sources are compiled with -fobjc-nonfragile- 
abi; Here are two compile commands from yesterday's build output  
(gnustep-make 2017-04-08):

Base:
+ clang NSThread.m -c -MMD -MP -DGNUSTEP_TARGET_DIR="." - 
DGNUSTEP_TARGET_CPU="ix86" -DGNUSTEP_TARGET_OS="linux-gnu" - 
DGNUSTEP_IS_FLATTENED="yes" -DLIBRARY_COMBO="gnu-gnu-gnu" - 
DGNUSTEP_BASE_INTERNAL=1 -Wall -Wdeclaration-after-statement -Wcast- 
align -DGNUSTEP -DGNUSTEP_BASE_LIBRARY=1 -DGNU_RUNTIME=1 - 
DGNUSTEP_BASE_LIBRARY=1 -fno-strict-aliasing -fexceptions -fobjc- 
exceptions -D_NATIVE_OBJC_EXCEPTIONS -fobjc-nonfragile-abi - 
D_NONFRAGILE_ABI -pthread -fPIC -DDEBUG -fno-omit-frame-pointer -Wall - 
DGSWARN -DGSDIAGNOSE -Wno-import -g -fgnu-runtime -fgnu-runtime - 
fconstant-string-class=NSConstantString -I../Headers -I./. -I. -I/home/ 
josh/GNUstep/Library/Headers -I/usr/GNUstep/Local/Library/Headers -I/ 
usr/GNUstep/System/Library/Headers -I/usr/GNUstep/Local/Library/ 
Headers -I/usr/GNUstep/Local/Library/Headers -I/usr/GNUstep/System/ 
Library/Headers -I/usr/GNUstep/Local/Library/Headers -I/usr/include/ 
libxml2 -I/usr/include/p11-kit-1 -o obj/libgnustep-base.obj/NSThread.m.o

GUI:
+ clang NSGraphicsContext.m -c -MMD -MP -DGNUSTEP_TARGET_DIR="." - 
DGNUSTEP_TARGET_CPU="ix86" -DGNUSTEP_TARGET_OS="linux-gnu" - 
DLIBRARY_COMBO="gnu-gnu-gnu" -DGNUSTEP_BASE_HAVE_LIBXML=1 - 
DBACKEND_BUNDLE=1 -DGNUSTEP -DGNUSTEP_BASE_LIBRARY=1 - 
DGNU_GUI_LIBRARY=1 -DGNU_RUNTIME=1 -DGNUSTEP_BASE_LIBRARY=1 -fno- 
strict-aliasing -fexceptions -fobjc-exceptions - 
D_NATIVE_OBJC_EXCEPTIONS -fobjc-nonfragile-abi -D_NONFRAGILE_ABI - 
pthread -fPIC -DDEBUG -fno-omit-frame-pointer -Wall -DGSWARN - 
DGSDIAGNOSE -Wno-import -g -fgnu-runtime -Wall -fconstant-string- 
class=NSConstantString -I../Headers/Additions -I../Headers -I./. -I. - 
I/home/josh/GNUstep/Library/Headers -I/usr/GNUstep/Local/Library/ 
Headers -I/usr/GNUstep/System/Library/Headers -I/usr/include/libpng16 - 
o obj/libgnustep-gui.obj/NSGraphicsContext.m.o


> If so, would it be possible for you to compile the relevant -gui  
> file and NSThread.m with -S (produce assembly, don’t compile) and  
> send me the resulting output?


   The attached assembly files were created by building the GS  
frameworks with the --save-temps option added to gnustep-make's  
INTERNAL_OBJCFLAGS.

gs-assembly.tar.gz contains 3 files: NSAutoreleasePool.s,  
NSGraphicsContext.s, NSThread.s

The segmentation fault is the result of two events:
-[NSAutoreleasePool dealloc] in Base gets the address of  
GSCurrentThread()->_autorelease_vars (struct), and passes it through  
several local functions, which overwrite its struct values.
-[NSGraphicsContext setCurrentContext:] in GUI assigns a value to  
GSCurrentThread()->_gcontext (the ivar right after _autorelease_vars),  
and crashes when sending a release message to its previous value.

SHA1(gs-assembly.tar.gz)= a7a4f3c4a0dd45a4c284e29a29d3cd8a03bb2383


Cheers,

Josh

gs-assembly.tar.gz
Description: GNU Zip compressed data