[Bug 59556] New: GetSystemInfo returns host CPU count ignoring cgroup CPU limits inside containers (Yomawari: Lost in the Dark)

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=59556

            Bug ID: 59556
           Summary: GetSystemInfo returns host CPU count ignoring cgroup
                    CPU limits inside containers (Yomawari: Lost in the
                    Dark)
           Product: Wine
           Version: 11.5
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ntdll
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

GetSystemInfo returns the host machine's full processor count
(dwNumberOfProcessors) even when running inside a Linux container
with cgroup CPU limits applied.

For example, on a 16-core host with a container limited to 2 CPUs via
"docker run --cpus=2", GetSystemInfo still reports 16 processors.

Steps to reproduce:
1. Run Wine inside a Docker container with CPU limits:
   docker run --cpus=2 <wine-image> wine cmd /c "echo %NUMBER_OF_PROCESSORS%"
2. Observe that the reported processor count matches the host, not the cgroup
limit.

Expected results:
The processor count should reflect the cgroup CPU limit (2 in this example),
consistent with the behavior of `nproc` from GNU coreutils (version >= 9.8).

Actual results:
The processor count matches the host machine's total CPU count (e.g. 16).

This affects applications that scale their behavior based on the reported
processor count. Yomawari: Lost in the Dark
(https://store.steampowered.com/app/1998330/), for instance, shows significant
performance degradation when run in a CPU-limited container. Hot-patching
GetSystemInfo to return the cgroup-limited CPU count resolved the issue,
suggesting the game relies on this value to determine its thread count or
workload distribution.

Wine's `init_cpu_info()` in dlls/ntdll/unix/system.c uses
`sysconf(_SC_NPROCESSORS_ONLN)`, which returns the host CPU count and does not
account for cgroup v1/v2 CPU quotas (`cpu.max` / `cpu.cfs_quota_us`).

GNU coreutils 9.8 (September 2025) added the same kind of cgroup v2 awareness
to nproc: https://github.com/coreutils/coreutils/issues/108

Tested with Wine 11.5, Arch Linux, Docker with --cpus flag.

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