Comment 86 for bug 138611

------8<-------
 1 size_t fwrite(const void * __restrict ptr, size_t size, http://www-look-4.com/category/travel/
 2 size_t nmemb, register FILE * __restrict stream)
 3 {
 4 size_t retval; https://komiya-dental.com/category/technology/
 5 __STDIO_AUTO_THREADLOCK_VAR;
 6 http://www.iu-bloomington.com/category/technology/
 7 > __STDIO_AUTO_THREADLOCK(stream);
 8
 9 retval = fwrite_unlocked(ptr, size, nmemb, stream);
10 https://waytowhatsnext.com/category/technology/
11 __STDIO_AUTO_THREADUNLOCK(stream);
12 http://www.wearelondonmade.com/category/travel/
13 return retval;
14 }
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 http://www.jopspeech.com/category/travel/
Here, we are at line 7. Using the "next" command leads no where. However,
setting a breakpoint on line 9 and issuing "continue" works.
http://joerg.li/category/travel/
Looking at the assembly instructions reveals that we're dealing with the
critical section entry code [1] that should never be interrupted, in this
case by the debugger's implicit breakpoints: http://connstr.net/category/travel/

------8<-------
  ... http://embermanchester.uk/category/travel/
1 add_s r0,r13,0x38
2 mov_s r3,1
3 llock r2,[r0] <-.
4 brne.nt r2,0,14 --. | http://www.slipstone.co.uk/category/travel/
5 scond r3,[r0] | |
6 bne -10 --|--'
7 brne_s r2,0,84 <-' http://www.logoarts.co.uk/category/travel/
  ...
------>8-------
 http://www.acpirateradio.co.uk/category/travel/
Lines 3 until 5 (inclusive) are supposed to be executed atomically. Therefore,
GDB should never (implicitly) insert a breakpoint on lines 4 and 5, else the http://www.compilatori.com/category/travel/
program will try to acquire the lock again by jumping back to line 3 and
gets stuck in an infinite loop. https://www.webb-dev.co.uk/category/technology/

The solution is to make GDB aware of these patterns so it inserts breakpoints
after the sequence -- line 6 in this example.