AnachronautandClaude Opus 5
a131a90c67
The quotes are gone by the time a token is classified, so checkIfKeyword's test of token[0] == '#' matched the STRING "#Program" sitting in a program's Data Segment. It was read as the directive: the segment silently changed in the middle of the data, the string's nine bytes were charged to the Program cursor instead of the Data one, and every label defined after it came out nine bytes wrong - in a file that still had a valid header, a plausible length, and nothing to say about any of it. The only symptom was a program that jumped into the middle of an instruction. This is the FOURTH of the family. A string spelling a mnemonic assembled as that instruction; a string beginning with a zero was rejected as a malformed literal; a string in the Program Segment was discarded in silence. The instruction check and the literal check both carry a "not a STRING" guard already. This one did not, so it has one now, and it lives inside checkIfKeyword rather than at the call site so it cannot be left off again. Nothing had ever triggered it, because nothing had ever needed a directive's name as data. An assembler written FOR this machine necessarily does: it has to compare tokens against "#Program" and "#Data". It was found by building one and watching it fault on its second instruction. Test stringKeyword puts every directive name in a program's data and prints a label defined after them. Verified that it bites: without the fix the assembler refuses the file outright. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
49 lines
1.5 KiB
NASM
49 lines
1.5 KiB
NASM
; A program whose data contains the names of directives.
|
|
;
|
|
; The quotes are gone by the time the assembler looks at a token, so "#Program" written as
|
|
; a string looked exactly like the directive. It was read as one: the segment silently
|
|
; changed in the middle of the Data Segment, the string's nine bytes were charged to the
|
|
; Program cursor instead, and every label defined after it came out nine bytes wrong. The
|
|
; file still had a valid header and a plausible length, so nothing said a word - the only
|
|
; symptom was a program that jumped into the middle of an instruction.
|
|
;
|
|
; This is the fourth of that family. A string spelling a mnemonic assembled as that
|
|
; instruction, a string beginning with a zero was rejected as a malformed literal, a string
|
|
; in the Program Segment was discarded in silence, and now this.
|
|
;
|
|
; It came up because an assembler written FOR this machine has to compare tokens against
|
|
; the directive names, so it necessarily has them in its data. Nothing else ever did.
|
|
;
|
|
; What it checks: that the strings survive as strings, and that a label defined after them
|
|
; still points where it should. Everything after Directives would shift if the bug came
|
|
; back, so printing Message is the test.
|
|
;
|
|
; Written by Anachronaut
|
|
|
|
#Program
|
|
|
|
start:
|
|
SETD.0 Directives
|
|
CALL show
|
|
SETD.0 Message
|
|
CALL show
|
|
HALT
|
|
|
|
show:
|
|
LDA.0
|
|
BRA showDone
|
|
OUTA 0x00
|
|
INCD.0
|
|
BRI show
|
|
showDone:
|
|
RET
|
|
|
|
#Data
|
|
|
|
Directives:
|
|
"#Program #Data #Include #Vectors #Base #Align #Reserve
|
|
"
|
|
Message:
|
|
"and a label after them still points at itself
|
|
"
|