From 9bc6561588093a788c29f07579f9e4103864a752 Mon Sep 17 00:00:00 2001 From: Masatake YAMATO Date: Wed, 16 Apr 2014 15:33:07 +0900 Subject: [PATCH] unwind: implement automatic mmap cache invalidation A mmap cache belonging to a tcb was updated when a system call which changed the memory mapping was called. This implementation was assumed the mapping was changed only by the tcb. However, this assumption is incorrect if the target application is multi-threaded; more than two tcbs can shared the same memory mapping and a tcb can modify it without being noticed by the others. This change introduces a global integer variable mmap_cache_generation, and mmap_cache_generation field to struct tcb. The variable is incremented each time a process enters a syscall that can modify its memory mapping. Each tcb records the value of this variable at the moment if building its mmap cache. Every mmap cache associated with the given tcb can be validated by comparing its mmap_cache_generation field with the variable mmap_cache_generation. This implementation is inefficient. If strace attaches two processes which don't share the memory mapping, rebuilding mmap cache of a tcb triggered by another tcb's mmap system call is not necessary. Signed-off-by: Masatake YAMATO --- defs.h | 1 + unwind.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++--------- 2 files changed, 58 insertions(+), 11 deletions(-) diff --git a/defs.h b/defs.h index 70b42a88..464a968a 100644 --- a/defs.h +++ b/defs.h @@ -430,6 +430,7 @@ struct tcb { struct UPT_info* libunwind_ui; struct mmap_cache_t* mmap_cache; unsigned int mmap_cache_size; + unsigned int mmap_cache_generation; struct queue_t* queue; #endif }; diff --git a/unwind.c b/unwind.c index 5794801a..ef5a404c 100644 --- a/unwind.c +++ b/unwind.c @@ -74,9 +74,12 @@ struct queue_t { struct call_t *tail; struct call_t *head; }; + static void queue_print(struct queue_t *queue); +static void delete_mmap_cache(struct tcb *tcp, const char *caller); static unw_addr_space_t libunwind_as; +static unsigned int mmap_cache_generation; void unwind_init(void) @@ -107,7 +110,7 @@ unwind_tcb_fin(struct tcb *tcp) free(tcp->queue); tcp->queue = NULL; - unwind_cache_invalidate(tcp); + delete_mmap_cache(tcp, __FUNCTION__); _UPT_destroy(tcp->libunwind_ui); tcp->libunwind_ui = NULL; @@ -119,7 +122,7 @@ unwind_tcb_fin(struct tcb *tcp) * The cache must be refreshed after some syscall: mmap, mprotect, munmap, execve */ static void -alloc_mmap_cache(struct tcb* tcp) +build_mmap_cache(struct tcb* tcp) { unsigned long start_addr, end_addr, mmap_offset; char filename[sizeof ("/proc/0123456789/maps")]; @@ -192,13 +195,27 @@ alloc_mmap_cache(struct tcb* tcp) } fclose(fp); tcp->mmap_cache = cache_head; + tcp->mmap_cache_generation = mmap_cache_generation; + + DPRINTF("tgen=%u, ggen=%u, tcp=%p, cache=%p", + "cache-build", + tcp->mmap_cache_generation, + mmap_cache_generation, + tcp, tcp->mmap_cache); } /* deleting the cache */ -void -unwind_cache_invalidate(struct tcb* tcp) +static void +delete_mmap_cache(struct tcb *tcp, const char *caller) { unsigned int i; + + DPRINTF("tgen=%u, ggen=%u, tcp=%p, cache=%p, caller=%s", + "cache-delete", + tcp->mmap_cache_generation, + mmap_cache_generation, + tcp, tcp->mmap_cache, caller); + for (i = 0; i < tcp->mmap_cache_size; i++) { free(tcp->mmap_cache[i].binary_filename); tcp->mmap_cache[i].binary_filename = NULL; @@ -208,6 +225,33 @@ unwind_cache_invalidate(struct tcb* tcp) tcp->mmap_cache_size = 0; } +static bool +rebuild_cache_if_invalid(struct tcb *tcp, const char *caller) +{ + if ((tcp->mmap_cache_generation != mmap_cache_generation) + && tcp->mmap_cache) + delete_mmap_cache(tcp, caller); + + if (!tcp->mmap_cache) + build_mmap_cache(tcp); + + if (!tcp->mmap_cache || !tcp->mmap_cache_size) + return false; + else + return true; +} + +void +unwind_cache_invalidate(struct tcb* tcp) +{ + mmap_cache_generation++; + DPRINTF("tgen=%u, ggen=%u, tcp=%p, cache=%p", "increment", + tcp->mmap_cache_generation, + mmap_cache_generation, + tcp, + tcp->mmap_cache); +} + /* * walking the stack */ @@ -229,9 +273,9 @@ stacktrace_walk(struct tcb *tcp, unsigned long true_offset; if (!tcp->mmap_cache) - alloc_mmap_cache(tcp); - if (!tcp->mmap_cache || !tcp->mmap_cache_size) - return; + error_msg_and_die("bug: mmap_cache is NULL"); + if (tcp->mmap_cache_size == 0) + error_msg_and_die("bug: mmap_cache is empty"); symbol_name = malloc(symbol_name_size); if (!symbol_name) @@ -494,7 +538,7 @@ unwind_print_stacktrace(struct tcb* tcp) DPRINTF("tcp=%p, queue=%p", "queueprint", tcp, tcp->queue->head); queue_print(tcp->queue); } - else { + else if (rebuild_cache_if_invalid(tcp, __FUNCTION__)) { DPRINTF("tcp=%p, queue=%p", "stackprint", tcp, tcp->queue->head); stacktrace_walk(tcp, print_call_cb, print_error_cb, NULL); } @@ -509,7 +553,9 @@ unwind_capture_stacktrace(struct tcb *tcp) if (tcp->queue->head) error_msg_and_die("bug: unprinted entries in queue"); - stacktrace_walk(tcp, queue_put_call, queue_put_error, - tcp->queue); - DPRINTF("tcp=%p, queue=%p", "captured", tcp, tcp->queue->head); + if (rebuild_cache_if_invalid(tcp, __FUNCTION__)) { + stacktrace_walk(tcp, queue_put_call, queue_put_error, + tcp->queue); + DPRINTF("tcp=%p, queue=%p", "captured", tcp, tcp->queue->head); + } } -- 2.34.1