RFC: cross-libkvm/libthread_db/proc_service

[Kostik Belousov]

On Sat, Jul 19, 2008 at 10:59:29AM -0700, Marcel Moolenaar wrote:
> All,
> 
> We have a couple of interfaces/APIs that can't be used cross-platform.
> 
> Take for example libkvm. On a 32-bit platform, we can't typically use
> libkvm on a 64-kernel, because the libkvm interface uses u_long for
> the target address, which on 32-bit platforms is 32 bits wide.
> 
> Likewise, libthread_db and proc_service are designed for native use
> only and need API tweaks to work in a cross-environment. Both use
> psaddr_t to represent a target address, which is defined as a void*
> in <sys/procfs.h>.
> 
> I'd like to change those interfaces/APIs to allow them to be used in
> a cross-platform debugging environment. Basically, this means that a
> target address will have to be defined as a uint64_t. Other datatypes
> may also need to be retyped.
> 
> For libkvm in particular I don't want to redefine struct kinfo_proc,
> struct nlist, etc. While it could be useful in a hybrid 32/64-bit
> environment, the effect of such changes have too high a chance to
> trickle down various other components/interfaces. Thus, for libkvm
> the focus is on kvm_read() and kvm_write().
> 
> Suggested plan of attack:
> o  add kvm_xread() and kvm_xwrite() to the libkvm API to minimize
>    the overall impact. The new functions operate on a 64-bit target
>    address (psaddr_t).
> o  change psaddr_t from a void* to a 64-bit integral (sys/procfs.h)
>    This affects proc_service and libthread_db. And consequently our
>    threading support in GDB.
> 
> Comments/thoughts?

I do not object to the idea, but thing to consider is the backward
compatibility. In other words, how much harder would it be to run,
e.g., an RELENG_7 jail on the current kernel after the change ?
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