linprocfs: Skip printing of the guard page in the /proc/self/maps

To calculate the base (lowest addressable) address of the stack of the
initial thread glibc parses /proc/self/maps.
In fact, the base address is calculated as 'to' value of stack entry of the
/proc/self/maps - stack size limit (if the stack grows down).
The base address should fit in between preceding entry and stack entry of
the /proc/self/maps.
In FreeBSD, since 19bd0d9 (Implement address space guards), we actually
have two mappings for the stack region. The first one is the no-access
mapping for the region the stack can grow into (guard page), and the
second - initial stack region with size sgrowsiz.
The first mapping confuses Glibc, in the end which is improperly
calculate stack size and the base address.

PR:			253337
Reviewed by:		kib
Differential revision:	https://reviews.freebsd.org/D35537
MFC after:		2 week

(cherry picked from commit ef1976ccf5420d0912afcb49733c7a88643069da)

1 files changed, 7 insertions, 1 deletions

diff --git a/sys/compat/linprocfs/linprocfs.c b/sys/compat/linprocfs/linprocfs.c
index 6cf25350d9e8..714c4ee4a84c 100644
--- a/sys/compat/linprocfs/linprocfs.c
+++ b/sys/compat/linprocfs/linprocfs.c
@@ -1307,7 +1307,13 @@ linprocfs_doprocmaps(PFS_FILL_ARGS)
 	VM_MAP_ENTRY_FOREACH(entry, map) {
 		name = "";
 		freename = NULL;
-		if (entry->eflags & MAP_ENTRY_IS_SUB_MAP)
+		/*
+		 * Skip printing of the guard page of the stack region, as
+		 * it confuses glibc pthread_getattr_np() method, where both
+		 * the base address and size of the stack of the initial thread
+		 * are calculated.
+		 */
+		if ((entry->eflags & (MAP_ENTRY_IS_SUB_MAP | MAP_ENTRY_GUARD)) != 0)
 			continue;
 		e_prot = entry->protection;
 		e_start = entry->start;