The Itanium processor, part 5: The GP register, calling functions, and function pointers

Raymond Chen July 31, 2015 Jul 31, 2015 07/31/15

We saw a brief mention of the gp register last time, where we saw it used when we calculated the address of a global variable. The only addressing mode supported by the Itanium processor is register indirect (possibly with post-increment). There is no absolute addressing mode. If you want to access a global variable, you need to calculate its...

The Itanium processor, part 3b: How does spilling actually work?

Raymond Chen July 30, 2015 Jul 30, 2015 07/30/15

Answering some interesting questions that arose yesterday. I didn't know the answers either, so I went and read the manual, specifically Volume 2 (IA-64 System Architecture), chapter 6 (IA-64 Register Stack Engine). Evan asks, Is the spilling to the stack done by the hardware, or does it trap into the OS?" According to the manual: The RSE ...

The Itanium processor, part 4: The Windows calling convention, leaf functions

Raymond Chen July 30, 2015 Jul 30, 2015 07/30/15

Last time, we looked at the general rules for parameter passing on the Itanium. But those rules are relaxed for leaf functions (functions which call no other functions). Before we start, I need to correct some of the explanation I had given when introducing the calling convention. I used that explanation because it makes for an easier ...

The Itanium processor, part 3: The Windows calling convention, how parameters are passed

Raymond Chen July 29, 2015 Jul 29, 2015 07/29/15

The calling convention on Itanium uses a variable-sized register window. The mechanism by which this is done is rather complicated, so I'm first going to present a conceptual version, and then I'll come back and fix up some of the implementation details. For today, I'm just going to talk about how parameters are passed. There are other aspects...

The Itanium processor, part 2: Instruction encoding, templates, and stops

Raymond Chen July 28, 2015 Jul 28, 2015 07/28/15

Instructions on Itanium are grouped into chunks of three, known as bundles, and each of the three positions in a bundle is known as a slot. A bundle is 128 bits long (16 bytes) and always resides on a 16-byte boundary, so that the last digit of the address is always zero. The Windows debugging engine disassembler shows the three slots as if ...

The Itanium processor, part 1: Warming up

Raymond Chen July 27, 2015 Jul 27, 2015 07/27/15

The Itanium may not have been much of a commercial success, but it is interesting as a processor architecture because it is different from anything else commonly seen today. It's like learning a foreign language: It gives you an insight into how others view the world. The next two weeks will be devoted to an introduction to the Itanium ...

Corrupted file causes application to crash; is that a security vulnerability?

Raymond Chen July 23, 2015 Jul 23, 2015 07/23/15

A security vulnerability report came in that went something like this: We have found a vulnerability in the XYZ application when it opens the attached corrupted file. The error message says, "Unhandled exception: System.OverflowException. Value was either too large or too small for an Int16." For a nominal subscription fee, you can learn ...