RISC-V: detect virtual address space at runtime using hwprobe#1296
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aurel32 wants to merge 1 commit into
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RISC-V: detect virtual address space at runtime using hwprobe#1296aurel32 wants to merge 1 commit into
aurel32 wants to merge 1 commit into
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The virtual address space on RISC-V is currently detected at build time by parsing /proc/cpuinfo. This works when the binary runs on the same hardware it was built, however running such a binary on a system with a larger address space just causes a segmentation fault. Replace the build time check with a runtime detection using the hwprobe interface (available since Linux 6.11, commit c9b8cd139c1d "riscv: hwprobe export highest virtual userspace address"). For older kernels, fallback to the default 48 bits. This is suboptimal on SV39 MMUs but still works.
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@microsoft-github-policy-service agree |
res2k
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May 18, 2026
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| # Check /proc/cpuinfo for an SV39 MMU and limit the virtual address bits. | ||
| # (this will skip the aligned hinting in that case. Issue #939, #949) | ||
| if (EXISTS /proc/cpuinfo) |
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Perhaps turn that into an explicit build time option? That way, people targeting an SV39 can at least explicitly request an appropriate number of bits.
(TBF, I have no idea how large that group may be.)
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... targeting an SV39 and an older kernel.
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I am not a big fan of configure options like that, because people don't really look at it until things are broken. I prefer when things work out of the box, but I understand your concern about supporting older kernels. What about adding a fallback parsing /proc/cpuinfo at runtime for older kernels?
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The virtual address space on RISC-V is currently detected at build time by parsing /proc/cpuinfo. This works when the binary runs on the same hardware it was built, however running such a binary on a system with a larger address space just causes a segmentation fault.
Replace the build time check with a runtime detection using the hwprobe interface (available since Linux 6.11, commit c9b8cd139c1d "riscv: hwprobe export highest virtual userspace address"). For older kernels, fallback to the default 48 bits. This is suboptimal on SV39 MMUs but still works.