Question

I’m trying to debug a function in 3rd party shared library. I’m having a hard time setting a breakpoint in the function as the application dies shortly after loading the library. Does anyone know of a way to set a pending break-point in mdb so the breakpoint is set shortly after the library is loaded?

Mustafa

Answer 1

What you call pending breakpoint is called deferred breakpoint in mdb; the way it’s being used is like this:

$ mdb /bin/ls
> ::bp libc.so.1`_init
> :r
mdb: stop at libc.so.1`_init
mdb: target stopped at:
libc.so.1`_init:save      %sp, -0x60, %sp

I.e. just turn the ::bp command around, <addr>::bp is direct (and requires the symbol / address to be present, already loaded), while ::bp <object`symbol> is deferred (and activated by the debugger when the specified object is first loaded). Using the object`symbol notation you can distinguish between identically-named functions in different libraries even:

> !ldd /bin/ls
        libsec.so.1 =>   /lib/libsec.so.1
        libc.so.1 =>     /lib/libc.so.1
        libavl.so.1 =>   /lib/libavl.so.1
        libm.so.2 =>     /lib/libm.so.2
> ::bp libsec.so.1`_init
> ::bp libc.so.1`_init
> ::bp libavl.so.1`_init
> ::bp libm.so.2`_init
> ::bp _init
> :r
mdb: stop at libc.so.1`_init
mdb: target stopped at:
libc.so.1`_init:save      %sp, -0x60, %sp
> :c
mdb: stop at libavl.so.1`_init
mdb: target stopped at:
libavl.so.1`_init:      save      %sp, -0x60, %sp
> :c
mdb: stop at libsec.so.1`_init
mdb: target stopped at:
libsec.so.1`_init:      save      %sp, -0x60, %sp
> :c
mdb: stop at _init
mdb: target stopped at:
_init:          save      %sp, -0x60, %sp

Enjoy debugging !