Linux 6.8 Will Let You Know When x86 32-bit Support Is Disabled

Linux 6.7 introduced the "ia32_emulation=" boot option for enabling/disabling support for x86 32-bit programs and the ability to execute 32-bit system calls. This is part of the effort of some Linux distributions working to restrict x86 32-bit user-space support where not needed in order to reduce the software attack surface while still having a boot-time option for those wanting to enable 32-bit support or to otherwise disable it if your kernel build keeps it enabled.

While one can check for the "ia32_emulation" option via /proc/cmdline to see if it was set, an oversight in Linux 6.7 was not explicitly communicating it via the kernel log (dmesg) when it's been overrode. With Linux 6.8 it will now be shown in the dmesg output when the x86 32-bit support is disabled with the following message:

"32-bit emulation disabled. You can reenable with ia32_emulation=on"

Again this is just about the x86 32-bit user-space support for those running Linux x86_64.

Old Linux 32-bit software can still run on modern Linux kernels, but with upcoming vendor kernels particularly in enterprise environments they may restrict it by default... In which case you just need to know about the "ia32_emulation=on" kernel option.

While I previously wrote about this change coming, passing it along now for those that missed it and because with the ongoing Linux 6.8 merge window it indeed landed as part of the x86/misc changes. In addition to now clearly stating when the 32-bit support is idsabled, there's a fix for a possible overflow when counting digits in num_digits() and also better documenting how /proc/cpuinfo should be used on x86/x86_64 systems.