Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
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@ryanc yeah uhhh off the top of my head
rax, rbx, rcx, rdx, r8-r15, rdi, rsi, rsp, rbp, rip and all the components thereof, and rflags
zmm0-zmm??? (can't remember how many we have now) plus the ymm/xmm components.
6 ye olde segment registers.
gdtr, ldtr, idtr, and another I forgot the name of.
maybe 5 control registers? they're numbered to 15 but most are reserved
8 debug registers
x87 FPU and MMX weirdness
hundreds of MSRs, hundreds more if you count CPUID leaves
plus internal regs
@gsuberland @ryanc And however many delay slots worth of them due to microcode shenanigans, and the debug registers (you can use them to store keymat if coldboot and DMA attacks are in your threatmodel).
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@ryanc yeah uhhh off the top of my head
rax, rbx, rcx, rdx, r8-r15, rdi, rsi, rsp, rbp, rip and all the components thereof, and rflags
zmm0-zmm??? (can't remember how many we have now) plus the ymm/xmm components.
6 ye olde segment registers.
gdtr, ldtr, idtr, and another I forgot the name of.
maybe 5 control registers? they're numbered to 15 but most are reserved
8 debug registers
x87 FPU and MMX weirdness
hundreds of MSRs, hundreds more if you count CPUID leaves
plus internal regs
@ryanc based on the reverse engineered microcode from Intel platforms we have RED unlock on I'd guess there are probably a hundred named internal microarchitectural registers at least (if we count unnamed we'll be here all week)
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@ryanc@infosec.exchange grins heavily with what extensions, may I ask? x86-64 is such a wide selector that I could only provide a rough range! <img class="not-responsive emoji" src="https://donotsta.re/emoji/akko/akko_giggle.png" title=":akko_giggle:" />
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@ryanc based on the reverse engineered microcode from Intel platforms we have RED unlock on I'd guess there are probably a hundred named internal microarchitectural registers at least (if we count unnamed we'll be here all week)
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@jn @ryanc@infosec.exchange my two emotional support registers for setting CPUID VendorId. xoxo VIA
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@ryanc Oh, that's easy!
x86-64
x86 = 64
x = 64⁄86
x = 32⁄43So it has at least 1.344 registers!
@catsalad your logic is flawless
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Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc There's not even 16-visible ISA registers.
If you *really* want to know how many uarch registers there are, I guess you can start by decapping the chip and counting DFF cells and SRAM bits
That will at least give a hard upper bound -
Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc
Long ago, I was starting to understand register renaming (the phrase "register file" gave me existencial doubts), and then they came with hyperthreading...
Now I feel CPU architecture is purely a spectator sport. -
@catsalad your logic is flawless
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@ryanc based on the reverse engineered microcode from Intel platforms we have RED unlock on I'd guess there are probably a hundred named internal microarchitectural registers at least (if we count unnamed we'll be here all week)
@ryanc and that's if you only count the internal registers for the main x86-64 cores and the surrounding cache/memory architecture.
if we include internal registers for UPI, PCIe, integrated graphics, TPM, IOMMU, VT-d/VT-x, and features like AMT and VROC, there's thousands of them.
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@ryanc based on the reverse engineered microcode from Intel platforms we have RED unlock on I'd guess there are probably a hundred named internal microarchitectural registers at least (if we count unnamed we'll be here all week)
@gsuberland @ryanc we have microcode for amd too
and it works on the newest cpus unlike on intel. there are a lot of internal registes you can access only through microcode -
Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc there are at least three
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Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc between 40 and transistor count / 3.
That's accurate, but not very precise.
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@gsuberland @ryanc we have microcode for amd too
and it works on the newest cpus unlike on intel. there are a lot of internal registes you can access only through microcode -
Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
A whole bunch of registers. If you run out of it, You might considder to stop using Macro Assembler and write GWBasic programs...
RAX, RBX, RCX, RDX, EAX, EBX, ECX, EDX, RDI, RSI, RBP, RSP, EDI, ESI, EBP, ESP, R8-R15, CS, DS, ES, FS, GS, SS, RIP, EIP, RFLAGS, EFLAGS, CR0-CR4, DR0-DR7, MSRs, SIMD, XMM0-XMM15, YMM0-YMM15, ZMM0-ZMM31, MM0--MM7,
ST0-ST7, MXCSR. -
R relay@relay.publicsquare.global shared this topic
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Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc Even for a Z80 it's not a trivial answer. (Yes I do know someone who wrote some code that used the R register.)
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Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc oh, that’s easy, actually. The answer is precisely one less than whatever the ideal number for your workload would be.
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Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc (xkcd 2867)
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@ryanc
Long ago, I was starting to understand register renaming (the phrase "register file" gave me existencial doubts), and then they came with hyperthreading...
Now I feel CPU architecture is purely a spectator sport. -
Saw a blog post titled "How many registers does an x86-64 CPU have?" and my immediate thought was "it's impossible to know and a sin to ask".
If you think the answer is 16, by the way, no it is not.
@ryanc easier question:
How many registers does the Motorola 68000 have?
It is also not 16.
