Re: tprof(8) ABI

[Kevin Bowling <kevin.bowling%kev009.com@localhost>]

Hi Nick,

My understanding is we are trying to capture a 64-bit PC from the
kernel into a structure that n32 userland reads. If we sign extend a
32-bit value read from the kernel, I'm not sure if we'd have the right
value in every case but I don't fully grasp the sign extension.  I
suppose we'd need to understand some other cases like x86 user on
amd64 or sparc on sparc64 too, and KASLR?

Using uint64_t in the structure definition should make it ABI
compatible for any arch userland to read the full 64-bit address.

On Sun, Apr 19, 2026 at 8:38 AM Nick Hudson <nick.hudson%gmx.co.uk@localhost> wrote:
>
> On 15/04/2026 05:09, Kevin Bowling wrote:
> > I implemented a tprof driver for mips octeon, but the port typically
> > runs an n32 userland.  This can be worked around by compiling an LP64
> > tprof(8), but I am not sure how that would work with the package sets.
> > Since it is a developer tool, I propose intentionally breaking the ABI
> > like the following patch.  I think it would improve other 32 on 64
> > situations at the cost of an ABI break, but it is a developer tool in
> > /usr/sbin so maybe this is the most pragmatic solution?
> > --- a/sys/dev/tprof/tprof_types.h
> > +++ b/sys/dev/tprof/tprof_types.h
> > @@ -50,7 +50,8 @@ typedef struct {
> >         uint32_t s_flags;       /* flags and counterID */
> >  #define TPROF_SAMPLE_INKERNEL  0x00000001 /* s_pc is in kernel address space */
> >  #define        TPROF_SAMPLE_COUNTER_MASK 0xff000000 /*
> > 0..(TPROF_MAXCOUNTERS-1) */
> > -       uintptr_t s_pc;         /* program counter */
> > +       uint64_t s_pc;          /* program counter; uint64_t for ABI compat
> > +                                * with 64-bit kernels and n32/ILP32 userland */
> >  } tprof_sample_t;
> >  typedef struct tprof_param {
>
> I have mostly completely forgotten MIPS ABIs, but shouldn't the PC just be sign extended?
>
>