Tk Source Code: View Ticket

Ticket UUID:	eedd795d987bd576164c247548395fe50396ddfe
Title:	sizeof(enum) != sizeof(int)
Type:	Bug	Version:	8.6
Submitter:	jan.nijtmans	Created on:	2022-05-05 13:28:36
Subsystem:	23. Option Parsing	Assigned To:	jan.nijtmans
Priority:	5 Medium	Severity:	Minor
Status:	Closed	Last Modified:	2022-05-08 20:22:39
Resolution:	Fixed	Closed By:	jan.nijtmans
		Closed on:	2022-05-08 20:22:39
Description:	When sizeof(enum) != sizeof(int), unaligned pointer access can happen when using TK_OPTION_STRING_TABLE. This is non-portable. The default behaviour of gcc/clang is to use 'int' as implementation for enum, but the -fshort-enum compiler option can be used to make enum storage more efficient. This cannot be used for Tk, currently. Problem description: In tkPlace.c, lines 70-72: Tk_Anchor anchor; ... (Tk_Anchor is an enum) BorderMode borderMode; ... (BorderMode is an enum too) If both Tk_Anchor and BorderMode are implemented as shorts, they fit together in an integer and borderMode will not be aligned on a 4-byte border. Further below: {TK_OPTION_ANCHOR, "-anchor", NULL, NULL, "nw", -1, Tk_Offset(Content, anchor), ... {TK_OPTION_STRING_TABLE, "-bordermode", NULL, NULL, "inside", -1, Tk_Offset(Content, borderMode), ... The `TK_OPTION_STRING_TABLE` option expects a `Tk_Offset` which is 4-byte aligned, as the variable (`borderMode` in this case) should be an integer. It isn't: it's an enum. As soon as the `-bordermode` option is used in the `place`, this will result in non-aligned access: crash! In total, I found 17 places where this is done wrong. Most of them have an int or a pointer following or preceding the offending variable, so no unaligned access will happen: some padding bytes will be written unintentionally, but that's all. the `-bordermode` is the only example found which really can go wrong. Proposed solution: Use a new flag TK_OPTION_ENUM_VAR, and check for this flag in TK_OPTION_STRING_TABLE parsing.
User Comments:	jan.nijtmans added on 2022-05-08 20:22:39: The 'revised_text' branch had some additional places where `TK_OPTION_ENUM_VAR` was lacking. Added those now. Closing jan.nijtmans added on 2022-05-05 13:56:36: Proposed fix here