From: Tom Tromey <tom@tromey.com>
To: Tom de Vries <tdevries@suse.de>
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH] [gdb/python] Throw MemoryError in inferior.read_memory if malloc fails
Date: Thu, 11 Apr 2024 10:07:29 -0600 [thread overview]
Message-ID: <875xwn51dq.fsf@tromey.com> (raw)
In-Reply-To: <20240411105257.15421-1-tdevries@suse.de> (Tom de Vries's message of "Thu, 11 Apr 2024 12:52:57 +0200")
>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
Tom> PR python/31631 reports a gdb internal error when doing:
Tom> ...
Tom> (gdb) python gdb.selected_inferior().read_memory (0, 0xffffffffffffffff)
Tom> utils.c:709: internal-error: virtual memory exhausted.
Tom> A problem internal to GDB has been detected,
Tom> further debugging may prove unreliable.
Tom> ...
Tom> Fix this by throwing a python MemoryError, such that we have instead:
Tom> ...
Tom> (gdb) python gdb.selected_inferior().read_memory (0, 0xffffffffffffffff)
Tom> Python Exception <class 'MemoryError'>:
Tom> Error occurred in Python.
Tom> (gdb)
Tom> ...
I tend to think you will regret opening this door, because I imagine
there are a large number of ways to crash gdb by passing nonsensical
values to Python APIs.
Tom> @request("readMemory")
Tom> @capability("supportsReadMemoryRequest")
Tom> def read_memory(*, memoryReference: str, offset: int = 0, count: int, **extra):
Tom> addr = int(memoryReference, 0) + offset
Tom> - buf = gdb.selected_inferior().read_memory(addr, count)
Tom> + oom = False
Tom> + try:
Tom> + buf = gdb.selected_inferior().read_memory(addr, count)
Tom> + except MemoryError:
Tom> + oom = True
Tom> + if oom:
Tom> + raise DAPException("Out of memory")
This should probably chain the memory error in the except block and
re-throw. See https://peps.python.org/pep-3134/
However I don't really understand why this is needed. Isn't the
exception already propagated back to the server thread?
Tom> + /* We used to use xmalloc, which does this trick to avoid malloc
Tom> + returning a nullptr for a valid reason. Keep doing the same. */
Tom> + if (length == 0)
Tom> + length = 1;
This is most likely a workaround for vendor implementations of malloc
that return NULL for malloc(0). See
https://www.gnu.org/software/gnulib/manual/html_node/malloc.html
However, here this is not necessary, because a 0-length memory read is
meaningless, and so this case can simply be reported as an error.
Tom
next prev parent reply other threads:[~2024-04-11 16:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 10:52 Tom de Vries
2024-04-11 16:07 ` Tom Tromey [this message]
2024-04-12 7:09 ` Tom de Vries
2024-04-15 16:16 ` Tom Tromey
2024-04-16 13:55 ` Tom de Vries
2024-04-16 19:10 ` Simon Marchi
2024-04-17 8:29 ` Tom de Vries
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