When Tcl is compiled with
To enable memory debugging, Tcl should be recompiled from scratch with
Once memory debugging support has been compiled into Tcl, the C
When memory debugging is enabled, whenever a call to ckalloc is made, slightly more memory than requested is allocated so the memory debugging code can keep track of the allocated memory, and eight-byte guard zones are placed in front of and behind the space that will be returned to the caller. (The size of the guard zone is defined by the C #define GUARD_SIZE in baseline/src/ckalloc.c -- it can be extended if you suspect large overwrite problems, at some cost in performance.) A known pattern is written into the guard zones and, on a call to ckfree, the guard zones of the space being freed are checked to see if either zone has been modified in any way. If one has been, the guard bytes and their new contents are identified, and a low guard failed or high guard failed message is issued. The guard failed message includes the address of the memory packet and the file name and line number of the code that called ckfree. This allows you to detect the common sorts of one-off problems, where not enough space was allocated to contain the data written, for example.
Normally, Tcl compiled with memory debugging enabled will make it easy to isolate a corruption problem. Turning on memory validation with the memory command can help isolate difficult problems. If you suspect (or know) that corruption is occurring before the Tcl interpreter comes up far enough for you to issue commands, you can set MEM_VALIDATE define, recompile tclCkalloc.c and rebuild Tcl. This will enable memory validation from the first call to ckalloc, again, at a large performance impact.
If you are desperate and validating memory on every call to
ckalloc and ckfree isn't enough, you can explicitly
Windows Server 2012. Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019.
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