Re: lapi/prctl: add more fallback definitions

Hi Andrea,

On Mon, 3 Aug 2026, Andrea Cervesato wrote:
> lapi/prctl: add more fallback definitions

--- [PATCH 1/2] ---

> +#ifndef PR_SET_MM_MAP
> +# define PR_SET_MM_MAP	14
> +#endif
> +#ifndef PR_SET_MM_MAP_SIZE
> +# define PR_SET_MM_MAP_SIZE	15
> +#endif
> +
> +#if !(HAVE_STRUCT_PRCTL_MM_MAP) && !defined(PR_SET_MM_MAP)

Could this struct guard depend only on HAVE_STRUCT_PRCTL_MM_MAP?

PR_SET_MM_MAP is defined immediately above, so !defined(PR_SET_MM_MAP) is
always false here. Systems missing struct prctl_mm_map therefore skip the
fallback even when HAVE_STRUCT_PRCTL_MM_MAP is false, and the second patch
cannot compile there.

--- [PATCH 2/2] ---

> +	SAFE_PRCTL(PR_SET_MM, PR_SET_MM_MAP_SIZE, (unsigned long)&sz, 0, 0);

Could this test set .min_kver = "3.18", or report TCONF when this operation
is unavailable?

PR_SET_MM_MAP_SIZE was added in Linux 3.18, while
CONFIG_CHECKPOINT_RESTORE predates it. A 3.5 through 3.17 kernel with that
configuration reaches setup(), rejects this operation, and SAFE_PRCTL()
reports TBROK for an unsupported reproducer feature.

Verdict - Needs revision

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