[Backtracing] Fix bug in Compact Image Map decoder.

al45tair · al45tair · commit 864f3dc023b1 · 2025-02-14T14:59:20.000Z
The `expand` opcode was being decoded incorrectly in the case where we
were trying to expand prefixes with codes of 64 or above.

rdar://144497804
diff --git a/docs/CompactImageMapFormat.md b/docs/CompactImageMapFormat.md
@@ -106,7 +106,7 @@ need to be stored in CIF data:
 |   8  | `/System/Applications`              |
 |   9  | `/Applications`                     |
 |  10  | `C:\Windows\System32`               |
-|  11  | `C:\Program Files\`                 |
+|  11  | `C:\Program Files`                  |
 
 Codes below 32 are reserved for future expansion of the fixed list.
 
diff --git a/stdlib/public/RuntimeModule/CompactImageMap.swift b/stdlib/public/RuntimeModule/CompactImageMap.swift
@@ -244,14 +244,15 @@ public enum CompactImageMapFormat {
           if (byte & 0x40) == 0 {
             code = Int(byte & 0x3f)
           } else {
-            let byteCount = Int(byte & 0x3f)
+            let byteCount = Int(byte & 0x3f) + 1
             code = 0
             for _ in 0..<byteCount {
               guard let byte = iterator.next() else {
                 return nil
               }
               code = (code << 8) | Int(byte)
             }
+            code += 64
           }
 
           #if DEBUG_COMPACT_IMAGE_MAP

Original file line number	Diff line number	Diff line change
`@@ -244,14 +244,15 @@ public enum CompactImageMapFormat {`
`244`	`244`	`if (byte & 0x40) == 0 {`
`245`	`245`	`code = Int(byte & 0x3f)`
`246`	`246`	`} else {`
`247`		`- let byteCount = Int(byte & 0x3f)`
	`247`	`+ let byteCount = Int(byte & 0x3f) + 1`
`248`	`248`	`code = 0`
`249`	`249`	`for _ in 0..<byteCount {`
`250`	`250`	`guard let byte = iterator.next() else {`
`251`	`251`	`return nil`
`252`	`252`	`}`
`253`	`253`	`code = (code << 8) \| Int(byte)`
`254`	`254`	`}`
	`255`	`+ code += 64`
`255`	`256`	`}`
`256`	`257`
`257`	`258`	`#if DEBUG_COMPACT_IMAGE_MAP`