New submission from Eryk Sun <[email protected]>:
In test.support, suppress_msvcrt_asserts sets the process error mode to include
SEM_FAILCRITICALERRORS, SEM_NOGPFAULTERRORBOX, SEM_NOALIGNMENTFAULTEXCEPT, and
SEM_NOOPENFILEERRORBOX. In contrast, the SuppressCrashReport context manager in
the same module only sets SEM_NOGPFAULTERRORBOX. It should also set
SEM_FAILCRITICALERRORS (i.e. do not display the critical-error-handler message
box).
Including SEM_NOOPENFILEERRORBOX wouldn't hurt, but it's not of much value
since it only affects the deprecated OpenFile function.
SEM_NOALIGNMENTFAULTEXCEPT may not be appropriate in a context manager, since
it's a one-time setting that can't be reverted, plus x86 and x64 processors
aren't even configured by default to generate alignment exceptions; they do
fixups in hardware.
---
Discussion
SEM_FAILCRITICALERRORS suppresses normal "hard error" reports sent by the
NtRaiseHardError system call -- or by ExRaiseHardError or IoRaiseHardError in
the kernel. If reporting a hard error isn't prevented by the error mode, the
report gets sent to the ExceptionPort of the process. Normally this is the
session's API port (e.g. "\Sessions\1\Windows\ApiPort"). A thread in the
session server process (csrss.exe) handles requests sent to this port. In the
case of a hard error, ultimately it creates a message box via
user32!MessageBoxTimeoutW.
For example:
NtRaiseHardError = ctypes.windll.ntdll.NtRaiseHardError
response = (ctypes.c_ulong * 1)()
With the default process error mode, the following raises a hard error dialog
for STATUS_UNSUCCESSFUL (0xC0000001), with abort/retry/ignore options:
>>> NtRaiseHardError(0xC000_0001, 0, 0, None, 0, response)
0
>>> response[0]
2
The normal response value for the above call is limited to abort (2), retry
(7), and ignore (4). The response is 0 if the process is set to fail critical
errors:
>>> msvcrt.SetErrorMode(msvcrt.SEM_FAILCRITICALERRORS)
0
>>> NtRaiseHardError(0xC000_0001, 0, 0, None, 0, response)
0
>>> response[0]
0
SEM_FAILCRITICALERRORS doesn't suppress all hard-error reporting. The system
also checks for an override flag (0x1000_0000) in the status code. This flag is
used in many cases, such as WinAPI FatalAppExitW. For example, the following
will report a hard error regardless of the process error mode:
>>> NtRaiseHardError(0xC000_0001 | 0x1000_0000, 0, 0, None, 0, response)
0
>>> response[0]
2
A common case that doesn't use the override flag is when the loader fails to
initialize a process.
For the release build of Python 3.10, for example, if "python310.dll" can't be
found, the loader tries to raise a hard error with the status code
STATUS_DLL_NOT_FOUND (0xC0000135). If the process error mode allows this, the
NtRaiseHardError system call won't return until the user clicks on the "OK"
button.
>>> os.rename('amd64/python310.dll', 'amd64/python310.dll.bak')
>>> # the following returns after clicking OK
>>> hex(subprocess.call('python'))
'0xc0000135'
With SEM_FAILCRITICALERRORS set, which by default gets inherited by a child
process, sending the hard error report is suppressed (i.e. NtRaiseHardError
returns immediately with a response of 0), and the failed child process
terminates immediately with the status code STATUS_DLL_NOT_FOUND.
>>> msvcrt.SetErrorMode(msvcrt.SEM_FAILCRITICALERRORS)
0
>>> # the following returns immediately
>>> hex(subprocess.call('python'))
'0xc0000135'
----------
messages: 371257
nosy: eryksun
priority: normal
severity: normal
stage: needs patch
status: open
title: SuppressCrashReport should set SEM_FAILCRITICALERRORS in Windows
type: enhancement
versions: Python 3.10
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Python tracker <[email protected]>
<https://bugs.python.org/issue40946>
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