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authorMike Frysinger <vapier@gentoo.org>2011-02-21 17:19:35 -0500
committerMike Frysinger <vapier@gentoo.org>2011-02-24 08:25:06 -0500
commit7a583ea370974998b4584595b9a4088fc070df1f (patch)
tree61c75c4cd5c9e40e3efb1e35861752aaa1af5596 /libpthread/linuxthreads.old
parent73d59554144f429b1cf0d4d7fa7de42bdf59ad92 (diff)
linuxthreads.old: fix nommu initial thread stack detection
Because the nommu address space is flat, and the application stack can literally be located anywhere, we cannot rely on the assumptions that the mmu port gets away with. Namely, that the first thread's stack lives at the top of memory and nothing will be created above it. Currently, the code rounds the current stack up a page and sets that as the "top" of the stack, and then marks the "bottom" of the stack as "1". Then as new threads are created, this assumption is further refined by slowly backing off the "bottom" when a new stack is created within the range of the initial stack. Simple ascii example (tid0 is the initial thread): 1 thread: [bos tid0 stack tos] 2 threads: [ tid0 stack ] [tid1 stack] 3 threads: [ tid0 stack ] [tid1 stack] [tid2 stack] As you can kind of see, this algorithm operates on one basic assumption: the initial top of stack calculation is the absolute top of the stack. While this assumption was fairly safe in the original nommu days of yore where the only file format was FLAT (which defaults to a 4KiB stack -- exactly 1 page), and memory was fairly tight, we can see that this falls apart pretty quickly as soon as the initial stack is larger than a page. The issue that crops up now is simple to hit: start an application with an 8KiB stack, execute some functions that put pressure on the stack so that it exceeds 4KiB, then start up some threads. The initial tos will be rounded up by a page, but this is actually the middle of the stack. Now when the initial thread returns from its functions (thus unwinding the stack) and tries to call something which calls back into libpthread, the thread_self() func fails to detect itself as the initial thread as the current stack is now above the tos. The __pthread_find_self() func kicks in, walks all the thread arrays, fails to find a hit, and then walks into uninitialized memory for the thread descriptor. Use of this garbage memory has obvious results -- things fall down & go boom. To address this, I extend the current algorithm to automatically scale back both the bottom and the top stack limits of the initial thread. We use the current stack pointer at "thread boot time" only as a single known point. The initial thread stack bottom is set to the bottom of memory and the initial thread stack top is set to the top of memory. Then as we create new stack threads, we figure out whether the new stack is above or below the single known good address, and then scale back either the tos or the bos accordingly. Reviewed-by: Steven J. Magnani <steve@digidescorp.com> Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Diffstat (limited to 'libpthread/linuxthreads.old')
-rw-r--r--libpthread/linuxthreads.old/internals.h24
-rw-r--r--libpthread/linuxthreads.old/pthread.c23
2 files changed, 30 insertions, 17 deletions
diff --git a/libpthread/linuxthreads.old/internals.h b/libpthread/linuxthreads.old/internals.h
index 637fcea62..110dd9d56 100644
--- a/libpthread/linuxthreads.old/internals.h
+++ b/libpthread/linuxthreads.old/internals.h
@@ -252,17 +252,25 @@ extern pthread_descr __pthread_main_thread;
Initially 0, meaning that the current thread is (by definition)
the initial thread. */
-/* For non-MMU systems also remember to stack top of the initial thread.
- * This is adapted when other stacks are malloc'ed since we don't know
- * the bounds a-priori. -StS */
-
extern char *__pthread_initial_thread_bos;
#ifndef __ARCH_USE_MMU__
-extern char *__pthread_initial_thread_tos;
+/* For non-MMU systems, we have no idea the bounds of the initial thread
+ * stack, so we have to track it on the fly relative to other stacks. Do
+ * so by scaling back our assumptions on the limits of the bos/tos relative
+ * to the known mid point. See also the comments in pthread_initialize(). */
+extern char *__pthread_initial_thread_tos, *__pthread_initial_thread_mid;
#define NOMMU_INITIAL_THREAD_BOUNDS(tos,bos) \
- if ((tos)>=__pthread_initial_thread_bos \
- && (bos)<__pthread_initial_thread_tos) \
- __pthread_initial_thread_bos = (tos)+1
+ do { \
+ char *__tos = (tos); \
+ char *__bos = (bos); \
+ if (__tos >= __pthread_initial_thread_bos && \
+ __bos < __pthread_initial_thread_tos) { \
+ if (__bos < __pthread_initial_thread_mid) \
+ __pthread_initial_thread_bos = __tos; \
+ else \
+ __pthread_initial_thread_tos = __bos; \
+ } \
+ } while (0)
#else
#define NOMMU_INITIAL_THREAD_BOUNDS(tos,bos) /* empty */
#endif /* __ARCH_USE_MMU__ */
diff --git a/libpthread/linuxthreads.old/pthread.c b/libpthread/linuxthreads.old/pthread.c
index ad392e34e..a8830b1a4 100644
--- a/libpthread/linuxthreads.old/pthread.c
+++ b/libpthread/linuxthreads.old/pthread.c
@@ -168,12 +168,10 @@ pthread_descr __pthread_main_thread = &__pthread_initial_thread;
char *__pthread_initial_thread_bos = NULL;
-/* For non-MMU systems also remember to stack top of the initial thread.
- * This is adapted when other stacks are malloc'ed since we don't know
- * the bounds a-priori. -StS */
-
#ifndef __ARCH_USE_MMU__
+/* See nommu notes in internals.h and pthread_initialize() below. */
char *__pthread_initial_thread_tos = NULL;
+char *__pthread_initial_thread_mid = NULL;
#endif /* __ARCH_USE_MMU__ */
/* File descriptor for sending requests to the thread manager. */
@@ -457,12 +455,19 @@ static void pthread_initialize(void)
setrlimit(RLIMIT_STACK, &limit);
}
#else
- /* For non-MMU assume __pthread_initial_thread_tos at upper page boundary, and
- * __pthread_initial_thread_bos at address 0. These bounds are refined as we
- * malloc other stack frames such that they don't overlap. -StS
+ /* For non-MMU, the initial thread stack can reside anywhere in memory.
+ * We don't have a way of knowing where the kernel started things -- top
+ * or bottom (well, that isn't exactly true, but the solution is fairly
+ * complex and error prone). All we can determine here is an address
+ * that lies within that stack. Save that address as a reference so that
+ * as other thread stacks are created, we can adjust the estimated bounds
+ * of the initial thread's stack appropriately.
+ *
+ * This checking is handled in NOMMU_INITIAL_THREAD_BOUNDS(), so see that
+ * for a few more details.
*/
- __pthread_initial_thread_tos =
- (char *)(((long)CURRENT_STACK_FRAME + getpagesize()) & ~(getpagesize() - 1));
+ __pthread_initial_thread_mid = CURRENT_STACK_FRAME;
+ __pthread_initial_thread_tos = (char *) -1;
__pthread_initial_thread_bos = (char *) 1; /* set it non-zero so we know we have been here */
PDEBUG("initial thread stack bounds: bos=%p, tos=%p\n",
__pthread_initial_thread_bos, __pthread_initial_thread_tos);