Difference between revisions of "Absurd texture name in error message"
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When a map has a missing flat or texture, the game aborts with an error message, either [[Error message#R_FlatNumForName: %s not found|R_FlatNumForName: %s not found]] or [[Error message#R_TextureNumForName: %s not found|R_TextureNumForName: %s not found]]. | When a map has a missing flat or texture, the game aborts with an error message, either [[Error message#R_FlatNumForName: %s not found|R_FlatNumForName: %s not found]] or [[Error message#R_TextureNumForName: %s not found|R_TextureNumForName: %s not found]]. | ||
| − | + | In their data structures in memory, [[sidedef]]s pack the upper, middle, and lower [[texture]] names (in that order) in arrays of eight characters, without using a separator: | |
| + | typedef struct | ||
| + | { | ||
| + | short textureoffset; | ||
| + | short rowoffset; | ||
| + | char toptexture[8]; | ||
| + | char bottomtexture[8]; | ||
| + | char midtexture[8]; | ||
| + | short sector; | ||
| + | } mapsidedef_t; | ||
| + | |||
| + | [[Sector]]s pack floor and ceiling [[flat]] names in a similar way: | ||
| + | typedef struct | ||
| + | { | ||
| + | short floorheight; | ||
| + | short ceilingheight; | ||
| + | char floorpic[8]; | ||
| + | char ceilingpic[8]; | ||
| + | short lightlevel; | ||
| + | short special; | ||
| + | short tag; | ||
| + | } mapsector_t; | ||
| + | |||
| + | When a texture or flat is missing, the error string is printed using the offending texture's name to be inserted as the <tt>%s</tt> token. Since {{wp|C (programming_language)|C}} uses {{wp|null-terminated string}}s, if the texture or flat name is full (it uses all eight characters available) then the formatting function will keep adding the next characters in memory until it finds a null byte. | ||
For example, if a sidedef is given a non-existent upper texture with a name using all eight characters, then the name of the next texture in order (middle texture) will be appended (regardless of whether it is missing or not). If that one is also full, the lower texture name will be appended too. And if the lower texture name is full, garbage characters will be added as the sidedef's sector number is processed, followed by the offsets, texture names, and sector number of the next sidedef, and so on, until a null byte is finally encountered, preferably before a {{wp|buffer overflow}} happens. | For example, if a sidedef is given a non-existent upper texture with a name using all eight characters, then the name of the next texture in order (middle texture) will be appended (regardless of whether it is missing or not). If that one is also full, the lower texture name will be appended too. And if the lower texture name is full, garbage characters will be added as the sidedef's sector number is processed, followed by the offsets, texture names, and sector number of the next sidedef, and so on, until a null byte is finally encountered, preferably before a {{wp|buffer overflow}} happens. | ||
[[Category:Errors and bugs]] | [[Category:Errors and bugs]] | ||
Revision as of 15:52, 25 February 2014
When a map has a missing flat or texture, the game aborts with an error message, either R_FlatNumForName: %s not found or R_TextureNumForName: %s not found.
In their data structures in memory, sidedefs pack the upper, middle, and lower texture names (in that order) in arrays of eight characters, without using a separator:
typedef struct
{
short textureoffset;
short rowoffset;
char toptexture[8];
char bottomtexture[8];
char midtexture[8];
short sector;
} mapsidedef_t;
Sectors pack floor and ceiling flat names in a similar way:
typedef struct
{
short floorheight;
short ceilingheight;
char floorpic[8];
char ceilingpic[8];
short lightlevel;
short special;
short tag;
} mapsector_t;
When a texture or flat is missing, the error string is printed using the offending texture's name to be inserted as the %s token. Since C uses null-terminated strings, if the texture or flat name is full (it uses all eight characters available) then the formatting function will keep adding the next characters in memory until it finds a null byte.
For example, if a sidedef is given a non-existent upper texture with a name using all eight characters, then the name of the next texture in order (middle texture) will be appended (regardless of whether it is missing or not). If that one is also full, the lower texture name will be appended too. And if the lower texture name is full, garbage characters will be added as the sidedef's sector number is processed, followed by the offsets, texture names, and sector number of the next sidedef, and so on, until a null byte is finally encountered, preferably before a buffer overflow happens.
