[issue38692] add a pidfd child process watcher

[Ahmed Sayeed]

Ahmed Sayeed <ahmedsayeed1982 at yahoo.com> added the comment:

------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 }
------>8-------
 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 http://the-hunters.org/technology/meta-symbol/ [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, http://fishingnewsletters.co.uk/crypto/kelleci-bay/
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. The solution is to make GDB aware of these patterns so it inserts breakpoints http://www.go-mk-websites.co.uk/services/kyoto/
after the sequence -- line 6 in this example.
 The solution is to make GDB aware of these patterns so it inserts breakpoints
after the sequence -- line 6 in this example. http://www.mconstantine.co.uk/services/new-zealand/
The solution is to make GDB aware of these patterns so it inserts breakpoints
after the sequence -- line 6 in this example

----------
components: +Build -asyncio
nosy: +ahmedsayeed1982 -aeros, asvetlov, benjamin.peterson, gousaiyang, hroncok, miss-islington, nanjekyejoannah, njs, yselivanov
versions: +Python 3.11 -Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38692>
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