ASSERT missing memory region w/ start/stop API for changes after dr_app_setup

# clients/bin64/tool.drcacheoff.burst_threads
pre-DR init
pre-DR start
pre-DR detach
<all_memory_areas is missing region 0x00007fb7c24a7000-0x00007fb7c2ca7000!>
<Application /work/dr/git/build_x64_dbg_tests/clients/bin64/tool.drcacheoff.burst_threads (23195).  Internal Error: DynamoRIO debug check failure: /work/dr/git/src/core/unix/memcache.c:446 false

The query is for the signal frame:

<all_memory_areas is missing region 0x00007ff1a2c62000-0x00007ff1a3462000!>

#1  0x00000000004fcd7c in internal_error (file=0x79e320 "/work/dr/git/src/core/unix/memcache.c", line=446, expr=0x79e79b "false")
    at /work/dr/git/src/core/utils.c:174
#2  0x00000000006eaca0 in memcache_query_memory (pc=0x7ff1a3460000 "", out_info=0x46d668d0) at /work/dr/git/src/core/unix/memcache.c:446
#3  0x00000000006ccf0b in query_memory_ex (pc=0x7ff1a3460000 "", out_info=0x46d668d0) at /work/dr/git/src/core/unix/os.c:8753
#4  0x00000000006ccf9a in get_memory_info (pc=0x7ff1a3460000 "", base_pc=0x0, size=0x0, prot=0x46d66924)
    at /work/dr/git/src/core/unix/os.c:8773
#5  0x00000000006d4f52 in copy_frame_to_stack (dcontext=0x46cd1c40, sig=12, frame=0x46d66ab8, sp=0x7ff1a3460878 "\375\005j", 
    from_pending=false) at /work/dr/git/src/core/unix/signal.c:2682
#6  0x00000000006e18b8 in sig_detach (dcontext=0x46cd1c40, frame=0x46d66ab8, detached=0x46d410f8)
    at /work/dr/git/src/core/unix/signal.c:6217
#7  0x00000000006e1ef9 in handle_suspend_signal (dcontext=0x46cd1c40, ucxt=0x46d66ac0, frame=0x46d66ab8)
    at /work/dr/git/src/core/unix/signal.c:6353

46d59000-46d5a000 r--p 00000000 00:00 0 
46d5a000-46d67000 rw-p 00000000 00:00 0                                  [stack:23277]
<...>
71412000-71436000 rw-p 00000000 00:00 0 
7ff1a1c5f000-7ff1a1c60000 ---p 00000000 00:00 0 
7ff1a1c60000-7ff1a2460000 rw-p 00000000 00:00 0                          [stack:23279]
7ff1a2460000-7ff1a2461000 ---p 00000000 00:00 0 
7ff1a2461000-7ff1a2c61000 rw-p 00000000 00:00 0 
7ff1a2c61000-7ff1a2c62000 ---p 00000000 00:00 0 
7ff1a2c62000-7ff1a3462000 rw-p 00000000 00:00 0 
7ff1a3462000-7ff1a3619000 r-xp 00000000 09:00 1313251                    /usr/lib64/libc-2.21.so

This is thread 23277. Why is it using 7ff1a2c62000-7ff1a3462000 as its stack if the maps shows a different region as the stack? Sigaltstack? My test doesn't set up an alt stack though.

(gdb) p *(thread_sig_info_t *)dcontext->signal_field $4 = { app_sigstack = { ss_sp = 0x0, ss_flags = 2, ss_size = 0 }, sigstack = { ss_sp = 0x46d59000, ss_flags = 0, ss_size = 57344 }, }

So the one labeled is in fact DR's alt stack and the missing region must be the main app stack. How did our scan miss it? dr_app_setup() is prior to thread creation is the reason I suppose and the start/stop API code never added any handling of later changes.

Should we do a full maps file scan on every dr_app_start? Or we can try to lazily query maps file whenever our cache misses. But the cache might have false positives, not just negatives, which will mess us up.

Not sure the code supports repeated scans, might take a little work. Need to throw out cache first, too.