fix simple 64-bit warnings/errors in signalmodule.c

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

BPO	400527
Nosy	@gvanrossum
Files	None: None

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GitHub fields: ```python assignee = 'https://github.com/gvanrossum' closed_at = created_at = labels = [] title = 'fix simple 64-bit warnings/errors in signalmodule.c ' updated_at = user = 'https://bugs.python.org/tmick' ``` bugs.python.org fields: ```python activity = actor = 'tmick' assignee = 'gvanrossum' closed = True closed_date = None closer = None components = ['None'] creation = creator = 'tmick' dependencies = [] files = ['2457'] hgrepos = [] issue_num = 400527 keywords = ['patch'] message_count = 5.0 messages = ['32799', '32800', '32801', '32802', '32803'] nosy_count = 2.0 nosy_names = ['gvanrossum', 'tmick'] pr_nums = [] priority = 'normal' resolution = None stage = None status = 'closed' superseder = None type = None url = 'https://bugs.python.org/issue400527' versions = [] ```

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

[gvanrossum]

I suppose this is to avoid a compiler warning more than a real problem? Trent, could you explain?

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

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[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

Fix warnings on 64-bit build build of signalmodule.c

• Though I know that SIG_DFL and SIG_IGN are just small constants, there are cast to function pointers so the appropriate Python call is PyLong_FromVoidPtr so that the pointer value cannot overflow on Win64 where sizeof(long) \< sizeof(void*).

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

As I understand signal handling, the signal() function takes a callback and returns a callback -- what they do is beside the point here. A callback can either be a function pointer or one of some special #define'd flags (SIG_DFL [default], SIG_IGN [ignore], others?). Practically speaking, these constants are likely to be 0 and 1 or, in any case, *not* big enough to overflow a 32-bit value. Theoretically, on Win64 there is room for overflow if these constants are treated as a long because, I think, they are only guaranteed to fit in a pointer (at least they are cast freely to function pointers).

So, effectively you are right. This patch is mainly to avoid compiler warnings, with a little healthy anal-retentiveness to boot.