Array overflow when no array is used

[Vincent Bernat]

 ❦ 30 septembre 2013 12:41 CEST, Vincent Bernat <bernat@luffy.cx> :

> For example:
>
> probe process("/usr/lib/php5/20090626/apc.so").function("apc_cache_make_file_key").return {
>     printf("%p\n", $key);
> }
>
> I get some values and a few seconds later, I get:
>
> ERROR: Array overflow, check MAXMAPENTRIES near identifier '$key' at ./apc-cache-miss.stp:4:20
>
> Where does it get an array?

I have looked at the generated code and discovered that local variables
are in fact a map keyed by TID. Since I have many concurrent processes,
I just increased MAXMAPENTRIES to get rid of the error. The error
message is quite unclear in this case.

I now needs to investigate why I get bad values for $key in some cases.

> typedef union _apc_cache_key_data_t {
>     struct {
>         apc_dev_t device;             /* the filesystem device */
>         apc_ino_t inode;              /* the filesystem inode */
>     } file;
>     struct {
>         const char *identifier;
>         int identifier_len;
>     } user;
>     struct {
>         const char *fullpath;
>         int fullpath_len;
>     } fpfile;
> } apc_cache_key_data_t;

Will such a structure be problematic for systemtap?
-- 
panic("mother...");
	2.2.16 /usr/src/linux/drivers/block/cpqarray.c