Re: [Mesa-dev] [PATCH] mesa: Add null pointer checks before dereferencing

[Brian Paul]

On 06/27/2013 04:51 PM, Anuj Phogat wrote:

On Thu, Jun 27, 2013 at 2:59 PM, Brian Paul <bri...@vmware.com> wrote:

On 06/27/2013 03:31 PM, Kenneth Graunke wrote:

On 06/27/2013 02:20 PM, Anuj Phogat wrote:

Assertions are not sufficient to check for null pointers as they don't
show up in release builds. So, add explicit null pointer checks in the
code.

Signed-off-by: Anuj Phogat <anuj.pho...@gmail.com>
---
   src/mesa/program/prog_execute.c | 10 ++++++++++
   1 file changed, 10 insertions(+)

diff --git a/src/mesa/program/prog_execute.c
b/src/mesa/program/prog_execute.c
index b902006..1bcbf6b 100644
--- a/src/mesa/program/prog_execute.c
+++ b/src/mesa/program/prog_execute.c
@@ -200,6 +200,8 @@ fetch_vector4(const struct prog_src_register *source,
   {
      const GLfloat *src = get_src_register_pointer(source, machine);
      ASSERT(src);
+   if (src == NULL)
+      return;

      if (source->Swizzle == SWIZZLE_NOOP) {
         /* no swizzling */
@@ -303,6 +305,8 @@ fetch_vector1(const struct prog_src_register *source,
   {
      const GLfloat *src = get_src_register_pointer(source, machine);
      ASSERT(src);
+   if (src == NULL)
+      return;

      result[0] = src[GET_SWZ(source->Swizzle, 0)];

@@ -320,6 +324,9 @@ fetch_vector1ui(const struct prog_src_register
*source,
                   const struct gl_program_machine *machine)
   {
      const GLuint *src = (GLuint *) get_src_register_pointer(source,
machine);
+   ASSERT(src);
+   if (src == NULL)
+      return 0;
      return src[GET_SWZ(source->Swizzle, 0)];
   }

@@ -1439,8 +1446,11 @@ _mesa_execute_program(struct gl_context * ctx,
            {
               const struct prog_src_register *source = &inst->SrcReg[0];
               const GLfloat *src = get_src_register_pointer(source,
machine);
+            ASSERT(src);
               GLfloat result[4];
               GLuint i;
+            if (src == NULL)
+               return GL_FALSE;
               for (i = 0; i < 4; i++) {
                  const GLuint swz = GET_SWZ(source->Swizzle, i);
                  if (swz == SWIZZLE_ZERO)

I don't like this.  I would just put an abort() below the _mesa_problem
in get_src_register_pointer.

For release builds I don't think that we ever want to abort/exit.

I think the only time get_src_register_pointer() can return NULL is for the
case of an invalid register file.  And we could instead return the ZeroVec
there.

Yes. This is a better option for get_src_register_pointer(). But I
think we can't return ZeroVec (a const float*) instead of NULL
in get_dst_register_pointer(). Should we return dummyReg instead?

Probably.

-Brian

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