The document analyzes the Blender 2.62 package, discussing its use of the PVS-Studio static analyzer to identify code quality issues and potential errors. It highlights the challenges posed by false positives due to the code's style and details several specific warnings and errors found during analysis, including incorrect macros and misprints. The findings underscore the importance of using tools like PVS-Studio to improve the quality of open-source software by allowing developers to address code vulnerabilities effectively.

1. Analyzing the Blender project with PVS-
Studio
Author: Andrey Karpov
Date: 23.04.2012
Abstract
We go on analyzing open source projects and making the software world better. This time we have
checked the Blender 2.62 package intended for creating 3D computer graphics.
Introduction
We regularly check various open source projects in C/C++ and make reports on check results. It allows
the world of open source programs to become better and us to tell programmers about the PVS-Studio
tool. Reports usually contain far not all the issues we find: since we are not familiar with projects, it
might be difficult for us to tell if certain fragments are real errors or just intricate code. It's OK. We
always give the authors of open source projects a free registration key for some time so that they could
analyze their source code more thoroughly. If a project is small, the trial version of PVS-Studio will be
quite enough to check it, since it provides the full functionality.
Readers often say in comments that checking open source projects is just advertisement of our tool.
They also give Coverity as an example of a tool that supports open source projects much more
intensively.
This comparison is not fair. Improving quality of open source products' codes has become a result of
realizing the Vulnerability Discovery and Remediation Open Source Hardening Project campaign. Within
the framework of this initiative, the Coverity company was granted $297,000 to support open source
projects [1]. That's not too much, of course, but if we were sponsored at least a bit too, we could be
more active analyzing open source projects.
About the Blender project
Blender is an open source package for creating 3D computer graphics which includes tools of designing,
animation, rendering, video postprocessing and also tools of making interactive games. Starting with
2002, Blender is an open source project (GNU GPL) and develops under active support by Blender
Foundation [2].
The Blender package is written in C, C++ and Python. We naturally checked parts in C and C++. The size
of the source code together with additional libraries is 68 Mbytes (2105 KLOC).
In this project, by the way, I seem to have met a function with the highest cyclomatic complexity I've
ever seen. This is the fast9_corner_score() function which can be found in the fast_9.c file. Its cyclomatic
complexity is 1767. But the function is actually simple, so you won't see anything incredible here.
Analysis was performed by the PVS-Studio static analyzer version 4.60.

2. False positives
The programming style used in Blender causes the PVS-Studio analyzer to generate a lot of false
positives among which real messages get lost. As a result, you cannot start working with Blender
without preliminarily customizing the analyzer. It's not that bad, however, as it may seem at first. It will
take you few efforts to greatly simplify your work when reading the report.
Let me clarify the above stated idea using numerical data. All in all, PVS-Studio generates 574 first-level
warnings referring to general analysis diagnostic rules. Just glancing through the report helps you
understand that most of the false positives refer to macros BLI_array_append, BLI_array_growone and
other macros starting with "BLI_array_".
These macros are safe but they are used quite often. The analyzer generates warnings V514 and V547
for the places where they are used. To get rid of these warnings you can add a special comment in the
BLI_array.h file that contains definitions of all these macros:
//-V:BLI_array_:514,547
This comment can be added anywhere in the text. After that you'll have to relaunch analysis but the
result will be quite noticeable: about 280 false positives will be eliminated.
All in all, the amount of first-level messages will be cut from 574 to 294 after adding one single
comment! This example shows very well that presence of a large number of false positives doesn't mean
that the report is difficult to analyze. The most part of noise can be often removed through quite little
effort.
To learn more about methods of suppressing false alarms, please read the corresponding
documentation section about suppression of false alarms.
Defects and odd code fragments we've found
Error in a macro
The sample given above shows how one can significantly reduce the number of false positives
suppressing warnings related to certain macros. But before suppressing a warning, make sure that there
is no real error. I know it from my own experience that when some warning concerns a macro, you feel
an urge not to investigate the reasons and ignore it right away. But don't hurry.
For example, consider the DEFAULT_STREAM macro that is used more than once in the Blender project.
It is long, so we'll cite only part of it here:
#define DEFAULT_STREAM
m[dC] = RAC(ccel,dC);
if((!nbored & CFBnd)) {

3. ....
PVS-Studio's warning: V564 The '&' operator is applied to bool type value. You've probably forgotten to
include parentheses or intended to use the '&&' operator. bf_intern_elbeem solver_main.cpp 567
Parentheses are arranged in a wrong way here. As a result, it is "!nbored" which is calculated first, and
only then the & operator is applied to a Boolean value. This is the correct code:
if(!(nbored & CFBnd)) {
Error while using a macro
An error here occurs not because of the macro, but because of a misprint when using it:
#define MAX2(x,y) ( (x)>(y) ? (x) : (y) )
static Scene *preview_prepare_scene(....)
{
...
int actcol = MAX2(base->object->actcol > 0, 1) - 1;
...
}
PVS-Studio's warning: V562 It's odd to compare 0 or 1 with a value of 1: (base->object->actcol > 0) > (1).
bf_editor_render render_preview.c 361
If you expand the macro, this is what you'll get:
int actcol = ( ( (base->object->actcol > 0) > (1) ) ?
(base->object->actcol > 0) : (1) ) - 1;
The "base->object->actcol > 0" expression always gives 0 or 1. The "[0..1] > 1" condition is always false.
It means that the statement can be simplified to:
int actcol = 0;
This is obviously not what the programmer intended. The fragment "> 0" must have been taken along by
accident when copying the "base->object->actcol" fragment.
This is the correct code:
int actcol = MAX2(base->object->actcol, 1) - 1;
Null pointer dereferencing
static int render_new_particle_system(...)
{

4. ParticleSettings *part, *tpart=0;
...
// tpart don't used
...
psys_particle_on_emitter(psmd,tpart->from,
tpa->num,pa->num_dmcache,tpa->fuv,
tpa->foffset,co,nor,0,0,sd.orco,0);
...
}
PVS-Studio's warning: V522 Dereferencing of the null pointer 'tpart' might take place. bf_render
convertblender.c 1788
The 'tpart' pointer in the render_new_particle_system() function is initialized by zero and never changed
until the moment of dereferencing. The function is quite complex and contains variables with similar
names. This is most likely a misprint and a different pointer should be used.
Identical functions
The analyzer has found a lot of functions with identical bodies. I didn't investigate these messages too
closely but I seemed to have found at least one error. Perhaps if Blender's authors use PVS-Studio, they
can find other similar fragments.
float uiLayoutGetScaleX(uiLayout *layout)
{
return layout->scale[0];
}
float uiLayoutGetScaleY(uiLayout *layout)
{
return layout->scale[0];
}
PVS-Studio's warning: V524 It is odd that the body of 'uiLayoutGetScaleY' function is fully equivalent to
the body of 'uiLayoutGetScaleX' function (interface_layout.c, line 2410). bf_editor_interface
interface_layout.c 2415
Intuition tells me that the uiLayoutGetScaleY() function should return the second item of the 'scale'
array:

5. float uiLayoutGetScaleY(uiLayout *layout)
{
return layout->scale[1];
}
Misprint in a homogeneous code block
void tcd_malloc_decode(....) {
...
x0 = j == 0 ? tilec->x0 :
int_min(x0, (unsigned int) tilec->x0);
y0 = j == 0 ? tilec->y0 :
int_min(y0, (unsigned int) tilec->x0);
x1 = j == 0 ? tilec->x1 :
int_max(x1, (unsigned int) tilec->x1);
y1 = j == 0 ? tilec->y1 :
int_max(y1, (unsigned int) tilec->y1);
...
}
PVS-Studio's warning: V537 Consider reviewing the correctness of 'x0' item's usage. extern_openjpeg
tcd.c 650
If you look attentively, you can notice an error occurring when assigning a new value to the 'y0' variable.
At the very end of the line, a member of the 'tilec->x0' class is used instead of 'tilec->y0'.
This code was most likely created through the Copy-Paste technology and the programmer forgot to
change the name of one variable during editing. This is the correct code:
y0 = j == 0 ? tilec->y0 :
int_min(y0, (unsigned int) tilec->y0);
Unspecified behavior
#define cpack(x)
glColor3ub( ((x)&0xFF), (((x)>>8)&0xFF), (((x)>>16)&0xFF) )
static void star_stuff_init_func(void)

6. {
cpack(-1);
glPointSize(1.0);
glBegin(GL_POINTS);
}
PVS-Studio's warning: V610 Unspecified behavior. Check the shift operator '>>. The left operand '(- 1)' is
negative. bf_editor_space_view3d view3d_draw.c 101
According to the C++ language standard, right shift of a negative value leads to unspecified behavior. In
practice this method is often used but you shouldn't do that: it cannot be guaranteed that the code will
always work as intended. This issue was discussed in the article "Wade not in unknown waters. Part
three".
I suggest rewriting this code in the following way:
cpack(UINT_MAX);
Similar dangerous fragments can be found in other functions:
V610 Undefined behavior. Check the shift operator '<<. The left operand '-1' is negative. bf_intern_ghost
ghost_ndofmanager.cpp 289
V610 Undefined behavior. Check the shift operator '<<. The left operand '(~0)' is negative. extern_bullet
btquantizedbvh.h 82
V610 Undefined behavior. Check the shift operator '<<. The left operand '(~0)' is negative. extern_bullet
btsoftbodyconcavecollisionalgorithm.h 48
Odd comparisons
static PyObject *bpy_bmlayercollection_subscript_slice(
BPy_BMLayerCollection *self,
Py_ssize_t start, Py_ssize_t stop)
{
...
if (start >= start) start = len - 1;
if (stop >= stop) stop = len - 1;
...
}

7. PVS-Studio's warnings:
V501 There are identical sub-expressions to the left and to the right of the '>=' operator: start >= start
bf_python_bmesh bmesh_py_types_customdata.c 442
V501 There are identical sub-expressions to the left and to the right of the '>=' operator: stop >= stop
bf_python_bmesh bmesh_py_types_customdata.c 443
The two conditions shown above never hold. I cannot tell for sure what exactly the developer intended
to write here. Perhaps the correct code should look as follows:
if (start >= len) start = len - 1;
if (stop >= len) stop = len - 1;
Here is one more odd comparison:
typedef struct opj_pi_resolution {
int pdx, pdy;
int pw, ph;
} opj_pi_resolution_t;
static bool pi_next_rpcl(opj_pi_iterator_t * pi) {
...
if ((res->pw==0)||(res->pw==0)) continue;
...
}
PVS-Studio's warning: V501 There are identical sub-expressions to the left and to the right of the '||'
operator: (res->pw == 0) || (res->pw == 0) extern_openjpeg pi.c 219
Most likely, it is not only the 'pw' variable that should be checked here, but 'ph' too:
if ((res->pw==0)||(res->ph==0)) continue;
Similar incorrect checks can be found here:
V501 There are identical sub-expressions to the left and to the right of the '||' operator: (res->pw == 0)
|| (res->pw == 0) extern_openjpeg pi.c 300
V501 There are identical sub-expressions to the left and to the right of the '||' operator: (res->pw == 0)
|| (res->pw == 0) extern_openjpeg pi.c 379

8. Identical actions
EIGEN_DONT_INLINE static void run(....)
{
...
if ((size_t(lhs0+alignedStart)%sizeof(LhsPacket))==0)
for (Index i = alignedStart;i<alignedSize;
i+=ResPacketSize)
pstore(&res[i],
pcj.pmadd(ploadu<LhsPacket>(&lhs0[i]),
ptmp0, pload<ResPacket>(&res[i])));
else
for (Index i = alignedStart;i<alignedSize;
i+=ResPacketSize)
pstore(&res[i],
pcj.pmadd(ploadu<LhsPacket>(&lhs0[i]),
ptmp0, pload<ResPacket>(&res[i])));
...
}
PVS-Studio's warning: V523 The 'then' statement is equivalent to the 'else' statement. bf_ikplugin
generalmatrixvector.h 268
Regardless of a condition, identical actions will be performed in the program. Perhaps it should be that
way. But this is most likely an error and the actions should be different.
Incorrect array filling
static int imb_read_tiff_pixels(....)
{
float *fbuf=NULL;
...
memset(fbuf, 1.0, sizeof(fbuf));
...
}

9. PVS-Studio's warning: V579 The memset function receives the pointer and its size as arguments. It is
possibly a mistake. Inspect the third argument. bf_imbuf tiff.c 442
The analyzer generates one warning, but the programmer actually managed to make 2 mistakes at once
in one line. We have noted it down for ourselves to implement a rule to find the second error - it should
be easy.
The first error. The 'fbuf' variable is a pointer, which means that sizeof(fbuf) will return the pointer size
instead of the array size. As a result, the memset() function will fill only the first several bytes in the
array.
The second error. The array consisting of items of the float type was intended to be filled with ones. But
the memset function handles bytes, so the array will be filled with trash.
A similar error can be found here:
V579 The memset function receives the pointer and its size as arguments. It is possibly a mistake.
Inspect the third argument. bf_imbuf tiff.c 450
Misprint in code clearing an array
int ntlGeometryObjModel::initModel(....)
{
...
ntlSetVec3f averts; averts.mVerts.clear();
ntlSetVec3f anorms; averts.mVerts.clear();
...
}
PVS-Studio's warning: V586 The 'clear' function is called twice for deallocation of the same resource.
Check lines: 176, 177. bf_intern_elbeem ntl_geometrymodel.cpp 177
I find it meaningless to clear an array in just now created objects. But I'm not familiar with the project,
so perhaps there is some sense in this operation. A misprint causes one and the same array to be
cleared both times. This is the correct code:
ntlSetVec3f averts; averts.mVerts.clear();
ntlSetVec3f anorms; anorms.mVerts.clear();
Double check
In Blender's code, we have found two identical checks written besides each other. The second condition
should be probably replaced with another. Or maybe this code is correct and the second check is
extraneous.
static void fcurve_add_to_list (....)

10. {
...
if (agrp == NULL) {
if (agrp == NULL) {
...
}
PVS-Studio's warning: V571 Recurring check. The 'if (agrp == ((void *) 0))' condition was already verified
in line 1108. bf_blenkernel ipo.c 1110
Odd code
void CcdPhysicsController::RelativeRotate(
const float rotval[9], bool local)
{
...
btMatrix3x3 drotmat(
rotval[0],rotval[4],rotval[8],
rotval[1],rotval[5],rotval[9],
rotval[2],rotval[6],rotval[10]);
...
}
PVS-Studio's warnings:
V557 Array overrun is possible. The '9' index is pointing beyond array bound. ge_phys_bullet
ccdphysicscontroller.cpp 867
V557 Array overrun is possible. The '10' index is pointing beyond array bound. ge_phys_bullet
ccdphysicscontroller.cpp 868
The 'rotval' pointer can refer to an array of any size. Perhaps the code is correct, and number [9] is just a
prompt for a human.
I cannot tell for sure if there is an error here or not. If the rotval array really consists of 9 items, an array
overrun will occur.
Uncreated file
void LogFileObject::Write(....) {

11. ...
// If there's no destination file, make one before outputting
if (file_ == NULL) {
...
// file_ don't used
...
fwrite(file_header_string, 1, header_len, file_);
...
}
PVS-Studio's warning: V575 The null pointer is passed into 'fwrite' function. Inspect the fourth
argument. extern_libmv logging.cc 870
According to the comment, if the file descriptor equals NULL, a new file shall be created. However,
before the fwrite() function is called, the 'filxe_' variable is not used anywhere. As a result, a null pointer
will be passed into the fwrite() function as a descriptor.
Using a pointer before verifying it against being a null pointer
PVS-Studio has an interesting rule V595. This diagnostic rule can be briefly posed in this way:
V595 is generated if:
1) a pointer is dereferenced;
2) the pointer is not changed anywhere further;
3) the pointer is compared to 0.
There are some exceptions to this rule, but let's not go into details.
This rule has both its advantage and disadvantage. The former is that you can find interesting errors
with its help. The latter is that it produces quite many false positives.
False positives are in most cases determined by the presence of unnecessary checks in macros. We
cannot fight this issue yet. Here is a typical example where a false positive is generated:
#define SAFE_RELEASE(p) { if (p) { Release(p); delete p; } }
X *p = ....;
p->Foo(); // <-- V595
SAFE_RELEASE(p);
The 'p' pointer is always not equal to NULL. But the code contains a check and the analyzer gets
suspicious about it.

12. We've made such a long introduction because the V595 warning is generated very often in Blender. All
in all, PVS-Studio has produced 119 warnings of this type. More than half of them are most likely to be
false positives. But authors should study the PVS-Studio-generated report themselves.
Let me give you only one example:
static struct DerivedMesh *dynamicPaint_Modifier_apply(....)
{
...
for (; surface; surface=surface->next) {
PaintSurfaceData *sData = surface->data;
if (surface &&
surface->format !=
MOD_DPAINT_SURFACE_F_IMAGESEQ &&
sData)
{
...
}
PVS-Studio's warning: V595 The 'surface' pointer was utilized before it was verified against nullptr.
Check lines: 1585, 1587. bf_blenkernel dynamicpaint.c 1585
The 'surface' pointer is used in the beginning to initialize the 'sData' variable. And only then the 'surface'
pointer is verified against being a null pointer.
Conclusions
1) Static analyzers are useful. Don't forget that they are most useful when you use them regularly. They
help you detect a lot of errors at the earliest stage and therefore avoid numerous painful debuggings,
but-reports from testers and users' complaints.
2) PVS-Studio sometimes produces a whole lot of false positives. But they usually can be eliminated
through quite little effort.
3) The trial version of PVS-Studio that can be downloaded from the website has the full functionality. It
will be sufficient to check small projects. Developers of large free open source programs will receive a
free key for some time from us.
References
1. Open Source Hardening Project. http://www.viva64.com/go.php?url=839
2. Wikipedia. Blender. http://www.viva64.com/go.php?url=841
3. Wikipedia. Cyclomatic complexity. http://www.viva64.com/go.php?url=595