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From: David Given on 12 Mar 2010 15:17
Here's another really, really obscure question. Any illumination will be
gratefully appreciated.

My app is using the Posix subsystem, Interix. I want to catch certain
null dereferences so I can emulate them in software and continue.

On a normal Unix I'd use sigaction with SA_SIGINFO for this; when the
dereference occurs the kernel sends me a SIGSEGV with information about
the exact state of the processor when the exception happened, so I can
just adjust the processor state and longjmp out.

Unfortunately Interix doesn't have SA_SIGINFO. This means I have to do
something else. Can anyone suggest what else I can do?

Just to make life more interesting, Interix doesn't let me use the Win32
APIs (which makes this post technically off-topic but I can't think of a
more appropriate place to ask). I *can*, however, use NT kernel APIs,
but these are so undocumented that unless I know what to look for I
won't find anything.

Are the structured event macros suitable for doing this? (They just
involve fiddling with %fs:0, so I don't know whether they're handled by
the kernel or whether they're a Win32 thing.) If so, does anyone have a
pointer to some code implementing resumable exceptions using them?

--
┌─── ｄｇ＠ｃｏｗｌａｒｋ．ｃｏｍ ───── http://www.cowlark.com ─────
│
│ life←{ ↑1 ⍵∨.^3 4=+/,¯1 0 1∘.⊖¯1 0 1∘.⌽⊂⍵ }
│ --- Conway's Game Of Life, in one line of APL
From: David Given on 13 Mar 2010 11:17
On 12/03/10 20:17, David Given wrote:
[...]
> Are the structured event macros suitable for doing this? (They just
> involve fiddling with %fs:0, so I don't know whether they're handled by
> the kernel or whether they're a Win32 thing.) If so, does anyone have a
> pointer to some code implementing resumable exceptions using them?

Naturally, shortly after posting my query I found the answer myself: the
AddVectoredExceptionHandler() function is just a shadow of NTDLL's
RtlAddVectoredExceptionHandler(), which is visible to Interix, and does
precisely what I want. I have it all working beautifully now.

--
┌─── ｄｇ＠ｃｏｗｌａｒｋ．ｃｏｍ ───── http://www.cowlark.com ─────
│
│ life←{ ↑1 ⍵∨.^3 4=+/,¯1 0 1∘.⊖¯1 0 1∘.⌽⊂⍵ }
│ --- Conway's Game Of Life, in one line of APL
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