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

[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

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

[Michael Teichgräber]

> 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?

Hi, I would say yes, as SP is r13 and LR is r14 on arm.
To run Russ' libtask on arm7 I used the Linux-arm-asm.s and
the arm-specific makecontext implementation from Linux.c,
as well as the following structures.

M.
--

enum {
	NREG = 16,
};

typedef
struct Mcontext
{
	u32int	gregs[NREG];	/* general registers */
} Mcontext;

typedef
struct ucontext
{
	Mcontext	uc_mcontext;
	sigset_t uc_sigmask;
	struct {
		void		*ss_sp;
		u16int	ss_size;
	} uc_stack;

} ucontext_t;

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

[Robert Raschke]

On 7/8/08, Michael Teichgräber <mt@wmipf.in-berlin.de> wrote:
> > 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?
>
> Hi, I would say yes, as SP is r13 and LR is r14 on arm.
> To run Russ' libtask on arm7 I used the Linux-arm-asm.s and
> the arm-specific makecontext implementation from Linux.c,
> as well as the following structures.
>
> M.
> --
>
> enum {
>        NREG = 16,
> };
>
> typedef
> struct Mcontext
> {
>        u32int  gregs[NREG];    /* general registers */
> } Mcontext;
>
> typedef
> struct ucontext
> {
>        Mcontext        uc_mcontext;
>        sigset_t uc_sigmask;
>        struct {
>                void            *ss_sp;
>                u16int  ss_size;
>        } uc_stack;
>
> } ucontext_t;
>

Thanks, that's gotten me quite a bit further. I can compile the whole
lot now and run quite a few of the commands, including rc, under the
ARM qemulation. Hurrah.

Next I need to figure out why I get segfaults for some. And then try
it on real HW.

Robby