Intel MPX, described in the following document for those who are new to it: https://software.intel.com/sites/default/files/managed/68/8b/319433-019.pdf
I'm not sure I understand how BNDLDX and BNDSTX work. Take for instance BNDSTX.
From the document (page 855):
BNDSTX is used to store the bounds associated with a buffer and the “pointer value” of the pointer to that buffer onto a bound table entry via address translation using a two-level structure, see Section 9.3.8. For example, the software has a buffer with bounds stored in BND0, the pointer to the buffer is in ESI, the following sequence will store the “pointer value” (the buffer) and the bounds into a configured bound table entry using address translation from the linear address associated with the base of a SIB-addressing form consisting of a base register and a index register:
MOV ECX, Dword ptr [ESI] ; store the pointer value in the index register ECX MOV EAX, ESI ; store the pointer in the base register EAX BNDSTX Dword ptr [EAX+ECX], BND0 ; perform address translation from the linear address of the base EAX and store bounds and pointer value ECX onto a bound table entry.
The example states that ESI contains some pointer, if so, then the first instruction mov ecx, dword ptr [esi] does a simple mov by indirect addressing and fetches a dword of whatever esi is pointing to into ecx, this is what I assume they mean by pointer value, or do they mean something else? What is the purpose of this, and how does this relate to the address translation that BNDSTX performs?
The second instruction seems intuitive enough, it simply wants to store this pointer to the buffer and makes a copy of it. However why this is strictly needed is also a bit strange. Does not BND0 already contain the start of the buffer? Does it not simply duplicate the lower bound pointer? And again, exactly what purpose this pointer value serves is not clear to me.
