Merge pull request #163 from jayrm/select-case-const

Select case as const, check jump table size

Add checks to ensure that while parsing the select case as const structure, that no case statement is out of range + or - 8192 from the first case statement range value. And that overall range is maximum of 8192 upon reaching the end select statement.

Author: jayrm

changelog.txt

@@ -49,6 +49,7 @@ Version 1.07.0
 - sf.net #893: 'Suffixes are only valid in -lang' error message showing incorrect -lang options allowed
 - fbc uses '-march=armv8-a' instead of invalid option '-march=aarch64' when passing options to gcc/LLVM (czsgaba)
 - rtlib: sys/io.h incorrectly included on systems that do not provide it.  It is used only for x86, x86_64 and is unnecessary for all other linux targets (armhf ,arm64, mips ....)
+- SELECT CASE AS CONST checks for ranges that would produce unreasonably large jump tables (greater than 8192 entries)
 
 
 Version 1.06.0

src/compiler/parser-compound-select-const.bas

@@ -223,6 +223,17 @@ sub cSelConstStmtNext( byval stk as FB_CMPSTMTSTK ptr )
 
 		'' first case?
 		if( swtbase = ctx.base ) then
+			'' we initially set the bias to the first value minus 
+			'' FB_MAXJUMPTBSLOTS.  This allows us to compare range values 
+			'' (fromvalue <= tovalue ) and check if ranges are too 
+			'' large.  Later, in cSelConstStmtEnd() we will adjust the 
+			'' bias to the lowest valid range value seen.
+
+			'' In terms of values used by the user:
+			'' minimum := bias
+			'' initial := bias + FB_MAXJUMPTBSLOTS
+			'' maximum := bias + FB_MAXJUMPTBSLOTS*2
+
 			stk->select.const_.bias = value - FB_MAXJUMPTBSLOTS
 		end if
 
@@ -253,10 +264,17 @@ sub cSelConstStmtNext( byval stk as FB_CMPSTMTSTK ptr )
 			continue do
 		end if
 
-		assert( value <= (FB_MAXJUMPTBSLOTS*2) )
-		assert( tovalue <= (FB_MAXJUMPTBSLOTS*2) )
 		assert( tovalue >= value )
 
+		'' check if emitted jump table would be too large. Even without this check, 
+		'' emitter can still build a valid jump table, as it will fill in gaps 
+		'' between ranges, however we limit the size here, as it might end up
+		''  unreasonably large.
+		if( (value >= FB_MAXJUMPTBSLOTS*2) or (tovalue >= FB_MAXJUMPTBSLOTS*2) ) then
+			errReport( FB_ERRMSG_RANGETOOLARGE )
+			continue do
+		end if
+
 		'' Add Case values in range
 		do
 			if( hSelConstAddCase( swtbase, value, label ) = FALSE ) then
@@ -323,6 +341,13 @@ sub cSelConstStmtEnd( byval stk as FB_CMPSTMTSTK ptr )
 		stk->select.const_.bias += adjust_bias
 	end if
 
+	'' Jump table too large? We haven't overflowed any internal structures
+	'' and the emitter will produce valid code, but to be consistent with
+	'' limits and documentation, report an error.
+	if( span >= FB_MAXJUMPTBSLOTS ) then
+		errReport( FB_ERRMSG_TOOMANYLABELS )
+	end if
+
 	astAdd( astBuildJMPTB( stk->select.sym, _
 	                       @ctx.casevalues(stk->select.const_.base), _
 	                       @ctx.caselabels(stk->select.const_.base), _

tests/compound/select-const-large-range-1.bas

@@ -0,0 +1,6 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+dim x as integer
+select case as const x
+case 1 to 8193
+end select

tests/compound/select-const-large-range-2.bas

@@ -0,0 +1,8 @@
+' TEST_MODE : COMPILE_ONLY_FAIL
+
+dim x as integer
+select case as const x
+case 8192
+case 8193
+case 1
+end select