I get the following errors from Valgrind as the first ones which I can't
understand:
==16606== Invalid write of size 8
==16606== at 0x7EB9660: ??? (in
/usr/lib/xorg/modules/drivers/i965_dri.so)
==16606== by 0x7EBCAD7: ??? (in
/usr/lib/xorg/modules/drivers/i965_dri.so)
==16606== by 0x797884D: ??? (in
/usr/lib/xorg/modules/drivers/i965_dri.so)
==16606== by 0x7B70B96: ??? (in
/usr/lib/xorg/modules/drivers/i965_dri.so)
==16606== by 0x7B73968: ??? (in
/usr/lib/xorg/modules/drivers/i965_dri.so)
==16606== by 0x7B79444: ??? (in
/usr/lib/xorg/modules/drivers/i965_dri.so)
==16606== by 0x4FF4609: ??? (in /usr/lib/libSDL2-2.0.so.0.12.0)
==16606== by 0x4FEC69E: ??? (in /usr/lib/libSDL2-2.0.so.0.12.0)
==16606== by 0x4FF0C45: ??? (in /usr/lib/libSDL2-2.0.so.0.12.0)
==16606== by 0x138141: textureFromText__oH9bIq9aVWxxLMPOKZa5z9bFQ
(@mtextures.nim.c:344) # this is the error
==16606== by 0x13AF13: main__e8Zc9b6ypCaQRJuBLKbydsw
(@mkorovan.nim.c:1377)
==16606== by 0x13C93F: NimMainModule (@mkorovan.nim.c:1912)
==16606== Address 0x7fccd34f9030 is not stack'd, malloc'd or (recently)
free'd
Run
In my application I have the following piece of code:
import sdl2, sdl2/ttf
type
Texture* = ptr TextureObj
TextureObj = object
data*: TexturePtr # from sdl2 lib
width*, height*: int
proc textureFromText*(r: RendererPtr; font: FontPtr, text: string,
fg: tuple[r,g,b,a: int]): Texture =
let surf: SurfacePtr = font.renderTextSolid(
text.cstring,
(fg.r.uint8,fg.g.uint8,fg.b.uint8,fg.a.uint8)
)
let texture: TexturePtr = r.createTextureFromSurface(surf)
# problem line
result = cast[Texture](alloc0(sizeof(Texture)))
result.data = texture
result.width = surf.w
result.height = surf.h
freeSurface(surf)
Run
which compiles to
N_LIB_PRIVATE N_NIMCALL(tyObject_TextureObj__s9blP5sVYLYsZltL4Bb1yzA*,
textureFromText__oH9bIq9aVWxxLMPOKZa5z9bFQ)(tyObject_RendererPtrcolonObjectType___RZ5I89cPVLRdJchBQYVCSfg*
r, tyObject_FontPtrcolonObjectType___aRlNW02x3t1nWe9bTYP3kng* font,
NimStringV2 text, tyTuple__FtZxsWeKlOo83uVL9c4OOmg* fg) {
tyObject_TextureObj__s9blP5sVYLYsZltL4Bb1yzA* result;
tyObject_Surface__sOGmuBWrSv9c4mZ0oaW1R1w* surf;
tyTuple__Xo4YhcsfLAmbGDNu1Obfcw T1_;
tyObject_TexturePtrcolonObjectType___6n0oqQPDsaMFNhtiJ29bOXw*
texture;
void* T2_;
nimfr_("textureFromText",
"/home/grfork/playground/nim/korovan/src/textures.nim");
result = (tyObject_TextureObj__s9blP5sVYLYsZltL4Bb1yzA*)0;
nimln_(31, "/home/grfork/playground/nim/korovan/src/textures.nim");
T1_.Field0 = ((NU8) ((*fg).Field0));
T1_.Field1 = ((NU8) ((*fg).Field1));
T1_.Field2 = ((NU8) ((*fg).Field2));
T1_.Field3 = ((NU8) ((*fg).Field3));
surf = Dl_16561790_(font, nimToCStringConv(text), T1_);
nimln_(38, "/home/grfork/playground/nim/korovan/src/textures.nim");
texture = Dl_16525674_(r, surf);
// problem line
nimln_(42, "/home/grfork/playground/nim/korovan/src/textures.nim");
T2_ = (void*)0;
T2_ = alloc0Impl__WrVG9abV9chlTLqkiXYLKwUg_3(((NI) 8));
result = ((tyObject_TextureObj__s9blP5sVYLYsZltL4Bb1yzA*) (T2_));
nimln_(43, "/home/grfork/playground/nim/korovan/src/textures.nim");
(*result).data = texture;
nimln_(44, "/home/grfork/playground/nim/korovan/src/textures.nim");
(*result).width = ((NI) ((*surf).w));
nimln_(45, "/home/grfork/playground/nim/korovan/src/textures.nim");
(*result).height = ((NI) ((*surf).h));
nimln_(46, "/home/grfork/playground/nim/korovan/src/textures.nim");
Dl_16525938_(surf);
popFrame();
return result;
}
Run
and the signature from SDL2 library for `createTextureFromSurface` is
proc createTextureFromSurface*(renderer: RendererPtr; surface: SurfacePtr):
TexturePtr {.
importc: "SDL_CreateTextureFromSurface".}
Run
In application code `textureFromText` is called in a loop many times a second
and its resulting object is destroyed every time with the `destroy` proc:
proc destroy*(texture: var Texture) =
if texture.isNil: return
if texture.data != nil: destroy texture.data
texture.data = nil
dealloc texture
texture = nil
Run
and removing it doesn't make a difference.
I'm just learning to use Valgrind and I'm not sure I understand what is going
on. How does this error occur?
