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It's exciting that Google specifically requires memory tagging support and the J extension (Standard Extension for Dynamically Translated Languages) from RISC-V

by mepian 4y ago

It's exciting that Google specifically requires memory tagging support and the J extension (Standard Extension for Dynamically Translated Languages) from RISC-V processors that are going to run Android: https://youtu.be/70O_RmTWP58?t=651 https://youtu.be/70O_RmTWP58?t=651

snvzz 4y ago
Defining the requirements is one point, one task in that list. Developing J is another. Note that J is not a ratified extension, or even close to being so. It has been moving slowly for years (been a low priority), and now it is finally getting some attention, as higher priority items (such as H, B, V and Zc) are either done or final stages.
- viraptor 4y ago
  Could Google pull another QUIC here? "Here's a thing we implemented and deployed, wanna polish it up and call http2?" (Yes, I'm ignoring nuance here)
  - snvzz 4y ago
    It could. Major vendors have contributed extensions before. Some of them evolved to standards, whereas some were only used as extra input.
  - Thorrez 4y ago
    SPDY became http2, QUIC became http3.
    - viraptor 4y ago
      You're right, but i can't edit anymore unfortunately.
pjmlp 4y ago
There is also "Member Day Session: J Extension Group Meeting" https://www.youtube.com/watch?v=0EEzXsA--9Y https://www.youtube.com/watch?v=0EEzXsA--9Y
bloopernova 4y ago
Not a hardware/chip person here, so I found this text helpful regarding memory tagging: "As one might expect, the Arm64 architecture uses 64-bit pointers to address memory. There is no need (yet!) for an address space that large, though, so normally only 48 of those bits are actually used by the hardware." ... "MTE allows the storage of a four-bit "key" in bits 59-56 of a virtual address — the lower "nibble" of the top byte. It is also possible to associate a specific key value with one or more 16-byte ranges of memory. When a pointer is dereferenced, the key stored in the pointer itself is compared to that associated with the memory the pointer references; if the two do not match, a trap may be raised." From this article at the ever-wonderful lwn.net: https://lwn.net/Articles/834289/ https://lwn.net/Articles/834289/

by mepian 4y ago

snvzz 4y ago

Defining the requirements is one point, one task in that list. Developing J is another. Note that J is not a ratified extension, or even close to being so. It has been moving slowly for years (been a low priority), and now it is finally getting some attention, as higher priority items (such as H, B, V and Zc) are either done or final stages.

viraptor 4y ago
Could Google pull another QUIC here? "Here's a thing we implemented and deployed, wanna polish it up and call http2?" (Yes, I'm ignoring nuance here)
- snvzz 4y ago
  It could. Major vendors have contributed extensions before. Some of them evolved to standards, whereas some were only used as extra input.
- Thorrez 4y ago
  SPDY became http2, QUIC became http3.
  - viraptor 4y ago
    You're right, but i can't edit anymore unfortunately.

pjmlp 4y ago

There is also "Member Day Session: J Extension Group Meeting" https://www.youtube.com/watch?v=0EEzXsA--9Y https://www.youtube.com/watch?v=0EEzXsA--9Y

bloopernova 4y ago

Not a hardware/chip person here, so I found this text helpful regarding memory tagging: "As one might expect, the Arm64 architecture uses 64-bit pointers to address memory. There is no need (yet!) for an address space that large, though, so normally only 48 of those bits are actually used by the hardware." ... "MTE allows the storage of a four-bit "key" in bits 59-56 of a virtual address — the lower "nibble" of the top byte. It is also possible to associate a specific key value with one or more 16-byte ranges of memory. When a pointer is dereferenced, the key stored in the pointer itself is compared to that associated with the memory the pointer references; if the two do not match, a trap may be raised." From this article at the ever-wonderful lwn.net: https://lwn.net/Articles/834289/ https://lwn.net/Articles/834289/