git: f75b1ff6e569 - main - Revert "libthr: Use kern.stacktop for thread stack calculation."

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=f75b1ff6e5698ac092aa33d66ea73a56f381ed99

commit f75b1ff6e5698ac092aa33d66ea73a56f381ed99
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2022-01-17 16:41:49 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2022-01-17 16:41:49 +0000

    Revert "libthr: Use kern.stacktop for thread stack calculation."
    
    The current ASLR stack gap feature will be removed, and with that the
    need for this change, and the kern.stactop sysctl, is gone.  Moreover,
    the approach taken in this revision does not provide compatibility for
    old copies of libthr.so, and the revision should have also updated
    __libc_map_stacks_exec().
    
    This reverts commit 78df56ccfcb40013a3e6904bd6d39836220c3550.
    
    Reviewed by:    kib
    MFC after:      1 week
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D33704
---
 lib/libthr/thread/thr_init.c    | 19 ++++++++-----------
 lib/libthr/thread/thr_private.h |  2 +-
 lib/libthr/thread/thr_stack.c   | 22 ++++++++++------------
 3 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/lib/libthr/thread/thr_init.c b/lib/libthr/thread/thr_init.c
index f2a66c406e85..82bde10a153e 100644
--- a/lib/libthr/thread/thr_init.c
+++ b/lib/libthr/thread/thr_init.c
@@ -61,7 +61,7 @@ __FBSDID("$FreeBSD$");
 #include "libc_private.h"
 #include "thr_private.h"
 
-char		*_stacktop;
+char		*_usrstack;
 struct pthread	*_thr_initial;
 int		_libthr_debug;
 int		_thread_event_mask;
@@ -388,7 +388,7 @@ init_main_thread(struct pthread *thread)
 	 * resource limits, so this stack needs an explicitly mapped
 	 * red zone to protect the thread stack that is just beyond.
 	 */
-	if (mmap(_stacktop - _thr_stack_initial -
+	if (mmap(_usrstack - _thr_stack_initial -
 	    _thr_guard_default, _thr_guard_default, 0, MAP_ANON,
 	    -1, 0) == MAP_FAILED)
 		PANIC("Cannot allocate red zone for initial thread");
@@ -402,7 +402,7 @@ init_main_thread(struct pthread *thread)
 	 *       actually free() it; it just puts it in the free
 	 *       stack queue for later reuse.
 	 */
-	thread->attr.stackaddr_attr = _stacktop - _thr_stack_initial;
+	thread->attr.stackaddr_attr = _usrstack - _thr_stack_initial;
 	thread->attr.stacksize_attr = _thr_stack_initial;
 	thread->attr.guardsize_attr = _thr_guard_default;
 	thread->attr.flags |= THR_STACK_USER;
@@ -427,7 +427,7 @@ init_main_thread(struct pthread *thread)
 	thread->attr.prio = sched_param.sched_priority;
 
 #ifdef _PTHREAD_FORCED_UNWIND
-	thread->unwind_stackend = _stacktop;
+	thread->unwind_stackend = _usrstack;
 #endif
 
 	/* Others cleared to zero by thr_alloc() */
@@ -464,13 +464,10 @@ init_private(void)
 		__thr_malloc_init();
 		/* Find the stack top */
 		mib[0] = CTL_KERN;
-		mib[1] = KERN_STACKTOP;
-		len = sizeof (_stacktop);
-		if (sysctl(mib, 2, &_stacktop, &len, NULL, 0) == -1) {
-			mib[1] = KERN_USRSTACK;
-			if (sysctl(mib, 2, &_stacktop, &len, NULL, 0) == -1)
-				PANIC("Cannot get kern.usrstack from sysctl");
-		}
+		mib[1] = KERN_USRSTACK;
+		len = sizeof (_usrstack);
+		if (sysctl(mib, 2, &_usrstack, &len, NULL, 0) == -1)
+			PANIC("Cannot get kern.usrstack from sysctl");
 		env_bigstack = getenv("LIBPTHREAD_BIGSTACK_MAIN");
 		env_splitstack = getenv("LIBPTHREAD_SPLITSTACK_MAIN");
 		if (env_bigstack != NULL || env_splitstack == NULL) {
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
index d6fb74bb4372..a5bbc5997d30 100644
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -724,7 +724,7 @@ extern int __isthreaded;
  * Global variables for the pthread kernel.
  */
 
-extern char		*_stacktop __hidden;
+extern char		*_usrstack __hidden;
 
 /* For debugger */
 extern int		_libthr_debug;
diff --git a/lib/libthr/thread/thr_stack.c b/lib/libthr/thread/thr_stack.c
index fe50bc76db5f..b08bafdd9417 100644
--- a/lib/libthr/thread/thr_stack.c
+++ b/lib/libthr/thread/thr_stack.c
@@ -149,20 +149,18 @@ singlethread_map_stacks_exec(void)
 {
 	int mib[2];
 	struct rlimit rlim;
-	u_long stacktop;
+	u_long usrstack;
 	size_t len;
 
 	mib[0] = CTL_KERN;
-	mib[1] = KERN_STACKTOP;
-	len = sizeof(stacktop);
-	if (sysctl(mib, nitems(mib), &stacktop, &len, NULL, 0) == -1) {
-		mib[1] = KERN_USRSTACK;
-		if (sysctl(mib, nitems(mib), &stacktop, &len, NULL, 0) == -1)
-			return;
-	}
+	mib[1] = KERN_USRSTACK;
+	len = sizeof(usrstack);
+	if (sysctl(mib, sizeof(mib) / sizeof(mib[0]), &usrstack, &len, NULL, 0)
+	    == -1)
+		return;
 	if (getrlimit(RLIMIT_STACK, &rlim) == -1)
 		return;
-	mprotect((void *)(uintptr_t)(stacktop - rlim.rlim_cur),
+	mprotect((void *)(uintptr_t)(usrstack - rlim.rlim_cur),
 	    rlim.rlim_cur, _rtld_get_stack_prot());
 }
 
@@ -215,7 +213,7 @@ _thr_stack_alloc(struct pthread_attr *attr)
 
 	/*
 	 * Use the garbage collector lock for synchronization of the
-	 * spare stack lists and allocations from stacktop.
+	 * spare stack lists and allocations from usrstack.
 	 */
 	THREAD_LIST_WRLOCK(curthread);
 	/*
@@ -251,11 +249,11 @@ _thr_stack_alloc(struct pthread_attr *attr)
 	}
 	else {
 		/*
-		 * Allocate a stack from or below stacktop, depending
+		 * Allocate a stack from or below usrstack, depending
 		 * on the LIBPTHREAD_BIGSTACK_MAIN env variable.
 		 */
 		if (last_stack == NULL)
-			last_stack = _stacktop - _thr_stack_initial -
+			last_stack = _usrstack - _thr_stack_initial -
 			    _thr_guard_default;
 
 		/* Allocate a new stack. */