[Bug 97321] Query INFO_LOG_LENGTH for empty info log should return 0

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97321

--- Comment #12 from Qiankun Miao <qiankun.miao at intel.com> ---
(In reply to Ian Romanick from comment #9)
> I guess the point is that you can't change one and not change the other.  I
> will not budge on that.
> 
> I also think it is wrong for glGetProgramInfoLog to not write a NUL when the
> info log is empty.  An application that does something like
> 
> 
>     glGetProgramInfoLog(prog, max_length, NULL, log);
>     printf("Info log:\n%s\n", log);
> 
> will print whatever garbage happens to be in log.  You may argue that the
> application is incorrect, but this usage is very, very common (among users
> of glGetProgramInfoLog).

max_length should make sure "log" doesn't overflow, otherwise it's a bug of
glGetProgramInfoLog implementation. 

Here is the usage of these two apis in chrome:
void Program::UpdateLogInfo() {
  GLint max_len = 0;
  glGetProgramiv(service_id_, GL_INFO_LOG_LENGTH, &max_len);
  if (max_len == 0) {
    set_log_info(nullptr);
    return;
  }
  std::unique_ptr<char[]> temp(new char[max_len]);
  GLint len = 0;
  glGetProgramInfoLog(service_id_, max_len, &len, temp.get());
  DCHECK(max_len == 0 || len < max_len);
  DCHECK(len == 0 || temp[len] == '\0');
  std::string log(temp.get(), len);
  log = ProcessLogInfo(log);
  set_log_info(log.empty() ? nullptr : log.c_str());
}

Application should handle max_len returned 0. If application didn't handle
that, glGetProgramInfoLog should make sure no buffer overflow for "max_len ==
0".

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