Watchpoint Event Specifications

The following are event specifications, syntax, and descriptions for watchpoint events.

access mode addr-exp, [byte-size-exp]

The memory specified by addr-exp has been accessed.

addr-exp is any expression that can be evaluated to produce an address. If a symbolic expression is used, the size of the region to be watched is automatically deduced, or you can override that with the `,` syntax. You can also use nonsymbolic, typeless address expressions; in which case, the size is mandatory. For example:

stop modify 0x5678, sizeof(Complex)

mode specifies that the memory was accessed. It can be composed of one or all of the letters:

mode can also contain one of:

In both cases the program counter will point at the offending instruction. The before and after refer to the side effect.

access is a replacement for modify. While both syntaxes work on Solaris 2.4, 2.5, 2.5.1, 2.6, and Solaris 7, on all of these operating environments except Solaris 2.6, access suffers the same limitations as modify and accepts only a mode of wa.

Limitations of access

No two matched regions may overlap.

change variable

The value of variable has changed.

cond cond-expr

The condition denoted by cond-expr evaluates to true. Any expression can be used for cond-expr, but it has to evaluate to an integral type.

modify addr-exp [ , byte-size ]

The specified address range has been modified. This is the older watchpoint facility.

addr-exp is any expression that can be evaluated to produce an address. If a symbolic expression is used, the size of the region to be watched is automatically deduced, or you can override that with the `,` syntax. You can also use nonsymbolic, typeless address expressions; in which case, the size is mandatory. For example:

stop modify 0x5678, sizeof(Complex)

Limitations of modify event-spec on Solaris 2.5.1

Addresses on the stack cannot be watched.

The event does not occur if the address being watched is modified by a system call.

Shared memory (MAP_SHARED) cannot be watched, because dbx cannot catch the other processes stores into shared memory. Also, dbx cannot properly deal with SPARC swap and ldstub instructions.

Addresses that do not exist at the time a handler for this event is created cannot be watched.

Multithreaded applications are prone to deadlock so mt watchpoints are nominally disallowed. They can be turned on by setting the dbx environment variable mt_watchpoints.