CPU does not support x86-64-v2

[naamaamiel]

Hi gem5 community!

I'm trying to compile and run my own simple binary workloads, and I'm running into the same issue any time that I try to run them. After the regular gem5 preamble, I see:

Fatal glibc error: CPU does not support x86-64-v2

and the simulation ends. This happens for every x86 workload I compile; it also happens on the "annotate this" binary from the 2024 bootcamp. It seems like an issue with the glibc version on my environment, but I'm not sure what the best way to address this is. Has anyone found a workaround for this? Thank you!

[seaver-olson]

I think I found a likely cause in gem5/src/arch/x86/X86ISA.py.
The default CPUID(0x1) return appears to be:

FamilyModelStepping = VectorParam.UInt32(
    [0x00020F51, 0x00000805, 0xEFDBFBFF, 0x00000209],
    "type/family/model/stepping and feature flags",
)

Based on the comment in the file, the order is EAX, EBX, EDX, ECX so this means the default value for CPUID(0x1).ECX is 0x00000209.
That seems relevant because CPUID(0x1).ECX is where features such as CMPXCHG16B, SSE4.1, SSE4.2 and POPCNT are reported and those are the x86-64-v2 baselines.

If those bits are not set in gem5’s default CPUID mask, that would be consistent with: Fatal glibc error: CPU does not support x86-64-v2

I am not sure whether this default is intentionally conservative or whether another config path overrides it, but this looks like a plausible repo-side explanation for the issue and may require either a CPUID override or a patch. For feature-level reference, I was looking here: https://en.wikipedia.org/wiki/X86-64#Microarchitecture_levels

[naamaamiel]

Thank you for the suggestion! I think you're right that this is what affects the supported x86 version. After manually changing the default bits (I am not sure if this will lead to simulation issues, but I wanted to see if I could get past the error), I was able to avoid the x86-64-v2 error, only to see the same for v3. Changing the bits for the corresponding v3 features didn't seem to work, though, and I'm not sure why. I'm wondering if there is another place being checked?

[seaver-olson]

It seems like gem5 supports the features required for v2 however it contains stubbed for extensions like AVX which are required in v3. I think the easiest solution for your current problem would be to target v2 in glibc so you do not need to worry about the stubs.