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SubjectRe: Compat 32-bit syscall entry from 64-bit task!?
On Thu, Jan 26, 2012 at 9:23 AM, Pedro Alves <palves@redhat.com> wrote:
> On 01/26/2012 12:59 AM, Jamie Lokier wrote:
>> Tracers mainly want to know if it's a 32-bit or 64-bit syscall, not
>> whether it's compat as such.
>
> Another idea, avoiding new PTRACE_EVENTs per arch, would be to make
> the abi32/abi64/compat/whatnot discriminator retrievable with PTRACE_GETEVENTMSG
> instead.  So you'd get PTRACE_EVENT_SYSCALL_ENTRY|EXIT, or the regular old
> 0x80|SIGTRAP, you'd still fetch the syscall number from $orig_ax (or whatever means
> for other archs), as usual, then have extra syscall info in PTRACE_GETEVENTMSG.
> I don't know if it'd be simple to make it possible to do PTRACE_GETEVENTMSG
> on a 0x80|SIGTRAP trap, but I imagine it so.
>
> -> wait
>  <- 0x80|SIGTRAP   (or PTRACE_EVENT_SYSCALL_ENTRY)
> -> read regs, find out syscall number
> -> PTRACE_GETEVENTMSG, figure out which entry mode was used.

This would require additional ptrace op per syscall entry.
Linus' method and event method wouldn't.

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vda
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