version 1.8, 2003/11/23 22:02:46
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version 1.9, 2003/11/23 22:52:29
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Line 33 Defer store-backtrace
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Line 33 Defer store-backtrace
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' noop IS store-backtrace |
' noop IS store-backtrace |
\ [THEN] |
\ [THEN] |
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\ Ok, here's the story about how we get to the native code for the |
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\ recovery code in case of a THROW, and why there is all this funny |
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\ stuff being compiled by TRY and RECOVER: |
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\ Upon a THROW, we cannot just return through the ordinary return |
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\ address, but have to use a different one, for code after the |
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\ RECOVER. How do we do that, in a way portable between the various |
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\ threaded and native code engines? In particular, how does the |
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\ native code engine learn about the address of the native recovery |
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\ code? |
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\ On the Forth level, we can compile only references to threaded code. |
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\ The only thing that translates a threaded code address to a native |
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\ code address is docol, which is only called with EXECUTE and |
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\ friends. So we start the recovery code with a docol, and invoke it |
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\ with PERFORM; the recovery code then rdrops the superfluously |
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\ generated return address and continues with the proper recovery |
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\ code. |
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\ At compile time, since we cannot compile a forward reference (to the |
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\ recovery code) as a literal (backpatching does not work for |
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\ native-code literals), we produce a data cell (wrapped in AHEAD |
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\ ... THEN) that we can backpatch, and compile the address of that as |
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\ literal. |
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\ Overall, this leads to the following resulting code: |
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\ ahead |
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\ +><recovery address>-+ |
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\ | then | |
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\ +-lit | |
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\ (try) | |
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\ ... | |
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\ (recover) | |
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\ ahead | |
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\ docol: <-----------+ |
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\ rdrop |
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\ ... |
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\ then |
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\ ... |
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\ !! explain handler on-stack structure |
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: (try) ( ahandler -- ) |
: (try) ( ahandler -- ) |
r> |
r> |
swap >r \ recovery address |
swap >r \ recovery address |
Line 48 Defer store-backtrace
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Line 91 Defer store-backtrace
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: try ( compilation -- orig ; run-time -- ) \ gforth |
: try ( compilation -- orig ; run-time -- ) \ gforth |
\ !! does not work correctly for gforth-native |
\ !! does not work correctly for gforth-native |
POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then |
POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then |
r> POSTPONE literal POSTPONE @ POSTPONE (try) ; immediate compile-only |
r> POSTPONE literal POSTPONE (try) ; immediate compile-only |
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: (recover) ( -- ) |
: (recover) ( -- ) |
\ normal end of try block: restore handler, forget rest |
\ normal end of try block: restore handler, forget rest |
Line 64 Defer store-backtrace
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Line 107 Defer store-backtrace
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: recover ( compilation orig1 -- orig2 ; run-time -- ) \ gforth |
: recover ( compilation orig1 -- orig2 ; run-time -- ) \ gforth |
\ !! check using a special tag |
\ !! check using a special tag |
POSTPONE (recover) |
POSTPONE (recover) |
POSTPONE else ; immediate compile-only |
POSTPONE else |
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docol: here 0 , 0 , code-address! \ start a colon def |
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postpone rdrop \ drop the return address |
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; immediate compile-only |
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: endtry ( compilation orig -- ; run-time -- ) \ gforth |
: endtry ( compilation orig -- ; run-time -- ) \ gforth |
POSTPONE then ; immediate compile-only |
POSTPONE then ; immediate compile-only |
Line 91 is catch
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Line 137 is catch
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r> lp! |
r> lp! |
r> fp! |
r> fp! |
r> swap >r sp! drop r> |
r> swap >r sp! drop r> |
rdrop 'throw |
rdrop 'throw r> perform |
THEN ; |
THEN ; |
is throw |
is throw |
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