Re: [Linux-ia64] Re: [RFC] proposed change for syscall stub

[Ulrich Drepper <drepper@redhat.com>]

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Peter Chubb wrote:
>>>>>>"David" = David Mosberger <davidm@napali.hpl.hp.com> writes:
> 
> 
> 
> really_new_syscall_stub: 
> 	adds r2 = SYSINFO_OFF, r13;; 
> 	ld8 r2 = [r2] 
> 	mov r9 = ar.pfs;; 
> 	mov r15 = SYSCALL_NR 
> 	mov b7 = r2
> 	br.call.sptk.many b6 = b7;; 
> 	cmp.eq p6,p0 = -1, r10 
> 	mov ar.pfs = r9 
> (p6)	br.cond.spnt.few syscall_error 
> 	br.ret.sptk.many rp;;
> 
> David> Here, SYSINFO_OFF is the offset in the user-level thread-control-block
> David> at which the system call entry point is stored.  glibc initializes
> David> this value to point to the following piece of code:
> 
> 
> The ABI only allows 16 bytes for the TCB pointed to by R13; 
> the first 8 bytes are a pointer to the dynamic thread vector, the
> second 8 bytes a pointer to the per-thread thread-library-private data
> (for linuxthreads, it points to a _pthread_descr)

I haven't yet decided how I'll handle this for IA-64 but I think the
thread descriptor should be placed before what the IA-64 ABI
unfortunately calls TCB.  I.e., SYSINFO_OFF will be a negative value.

- -- 
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Ulrich Drepper \    ,-----------------'   \ Mountain View, CA 94041 USA
Red Hat         `--' drepper at redhat.com `---------------------------
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