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zasm: have .fill generate an error on overflow

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Can possibly avoid a lot of debugging pain.
This commit is contained in:
Virgil Dupras 2019-11-13 22:24:58 -05:00
parent 8d46895dd3
commit 82995eb346
3 changed files with 22 additions and 11 deletions
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11
apps/zasm/README.md
View File

@ -121,15 +121,20 @@ allowed. An included file cannot have an `.inc` directive.
expression written as the second parameter. Example: expression written as the second parameter. Example:
`.equ foo 0x42+'A'` `.equ foo 0x42+'A'`
If the symbol specified has already been defined, no error occur and If the symbol specified has already been defined, no error occur and
the first value defined stays intact. This allows for "user override" the first value defined stays intact. This allows for "user override"
of programs. of programs.
**.fill**: Outputs the number of null bytes specified by its argument, an **.fill**: Outputs the number of null bytes specified by its argument, an
expression. Often used with `$` to fill our binary up to a certain expression. Often used with `$` to fill our binary up to a certain
offset. For example, if we want to place an instruction exactly at offset. For example, if we want to place an instruction exactly at
byte 0x38, we would precede it with `.fill 0x38-$`. byte 0x38, we would precede it with `.fill 0x38-$`.
The maximum value possible for `.fill` is `0xd000`. We do this to
avoid "overshoot" errors, that is, error where `$` is greater than
the offset you're trying to reach in an expression like `.fill X-$`
(such an expression overflows to `0xffff`).
**.org**: Sets the Program Counter to the value of the argument, an expression. **.org**: Sets the Program Counter to the value of the argument, an expression.
For example, a label being defined right after a `.org 0x400`, would For example, a label being defined right after a `.org 0x400`, would
have a value of `0x400`. Does not do any filling. You have to do that have a value of `0x400`. Does not do any filling. You have to do that

21
apps/zasm/directive.asm
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@ -201,8 +201,11 @@ handleFIL:
jr nz, .badfmt jr nz, .badfmt
call parseExpr call parseExpr
jr nz, .badarg jr nz, .badarg
push bc push bc ; --> lvl 1
push ix \ pop bc push ix \ pop bc
ld a, b
cp 0xd0
jr nc, .overflow
.loop: .loop:
ld a, b ld a, b
or c or c
@ -213,20 +216,22 @@ handleFIL:
dec bc dec bc
jr .loop jr .loop
.loopend: .loopend:
cp a ; ensure Z cp a ; ensure Z
pop bc pop bc ; <-- lvl 1
ret ret
.ioError: .ioError:
ld a, SHELL_ERR_IO_ERROR ld a, SHELL_ERR_IO_ERROR
jr .error jp unsetZ
.badfmt: .badfmt:
ld a, ERR_BAD_FMT ld a, ERR_BAD_FMT
jr .error jp unsetZ
.badarg: .badarg:
ld a, ERR_BAD_ARG ld a, ERR_BAD_ARG
.error: jp unsetZ
call unsetZ .overflow:
ret pop bc ; <-- lvl 1
ld a, ERR_OVFL
jp unsetZ
handleOUT: handleOUT:
push hl push hl

1
tools/tests/zasm/errtests.sh
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@ -54,6 +54,7 @@ chkerr ".inc" 19
chkerr ".inc foo" 19 chkerr ".inc foo" 19
chkerr "ld a, 0x100" 20 chkerr "ld a, 0x100" 20
chkerr ".db 0x100" 20 chkerr ".db 0x100" 20
chkerr $'nop \ nop \ nop\n.fill 2-$' 20
chkerr ".inc \"doesnotexist\"" 21 chkerr ".inc \"doesnotexist\"" 21
chkerr "foo:\\foo:" 22 chkerr "foo:\\foo:" 22
chkoom chkoom