[9fans] P9P libthread on Debian ARM vs. makecontext et al.

[Robert Raschke]

Hi,

I recently got myself a lovely Nokia N810 internet tablet. That runs
Debian ARM and I thought I'd have a stab at compiling P9P for it.
Unfortunately, the makecontext/swapcontext calls are not supported on
that platform by Debian.

I noticed that libthread/Linux.c has implementations of those two
functions for ARM. So I thought I try compiling libthread without
pthread support. This time, it's the mcontext_t (aka sigcontext)
struct that is causing an issue. The Debian ARM sigcontext struct
looks like this:

struct sigcontext {
    unsigned long trap_no;
    unsigned long error_code;
    unsigned long oldmask;
    unsigned long arm_r0;
...
    unsigned long arm_r10;
    unsigned long arm_fp;
    unsigned long arm_ip;
    unsigned long arm_sp;
    unsigned long arm_lr;
    unsigned long arm_pc;
    unsigned long arm_cpsr;
    unsigned long fault_address;
};

The code in Linux.c that implements makecontext() for ARM expects this
struct to contain a gregs array. I'm guessing that gregs is the same
as the enumerated arm_* ones above. So, would I be correct in assuming
that gregs[13] is arm_sp and gregs[14] is arm_lr?

Thanks,
Robby