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0 pointsgizmo68611y ago0 comments

You still are not guaranteed to clear the buffer like that.

  for (int i=0; i<len; i++){
    sensitiveBuffer[i]=random();
  }
  int sum=0;
  for (int i=0; i<len; i++){
    sum+=sensitiveBuffer[i];
  }
  volitileVar=sum;

Using loop fusion, the compiler can optimize this to: int sum=0; for (int i=0; i<len; i++){ sensitiveBuffer[i]=random(); sum+=sensitiveBuffer[i]; } volitileVar=sum;

Which it can then optimize to: int sum=0; for (int i=0; i<len; i++){ sum+=random(); } volitileVar=sum;

In fact, as the article points out, the compiler can legally transform:

  reallyZeroBuffer(sensitiveBuffer);

into

  pointlesslyCopy(sensitiveBuffer);
  reallyZeroBuffer(sensitiveBuffer);

0 comments

xxs11y ago

not like that: Not exactly like that: I didn't mean simple that way, more like hash alike. The 1st example is not optimal but shows the idea.

I disagree about "pointlessCopy". Of course it's permitted by the standard but it's not an optimization. Using such a broken compiler is beyond help.

------- volatileVar *= random(); for (int i=0;i<len;i++){ volatileVar+=buf[random()%len]+0x61c88647; buf[i]=volatileVar; } ===== static volatile uint volitileVar;

  for (int i=0; i<len; i++){
    sensitiveBuffer[i]=random();
  }

  for (int i=0; i<len; i++){
    volitileVar+=sensitiveBuffer[volatileVar%len];
  }

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