* Re: [PATCH] 2.4 force_successful_syscall()
2003-09-17 20:00 ` [PATCH] 2.4 force_successful_syscall() Marcelo Tosatti
@ 2003-09-17 21:41 ` Bjorn Helgaas
2003-09-18 5:42 ` Aneesh Kumar K.V
1 sibling, 0 replies; 4+ messages in thread
From: Bjorn Helgaas @ 2003-09-17 21:41 UTC (permalink / raw)
To: Marcelo Tosatti; +Cc: Marcelo Tosatti, linux-ia64, linux-kernel
On Wednesday 17 September 2003 2:00 pm, Marcelo Tosatti wrote:
>
> On Wed, 10 Sep 2003, Bjorn Helgaas wrote:
>
> > Here's a 2.4 backport of this change to 2.5:
> >
> > http://linux.bkbits.net:8080/linux-2.5/cset@1.1046.238.7?nav=index.html
> >
> > Alpha, ppc, and sparc64 define force_successful_syscall_return() in 2.5,
> > but since it's not obvious to me how to do it correctly in 2.4, I left
> > them unchanged.
>
> Whats the reasoning behing this patch?
Basically we don't want a large unsigned return value to be
misinterpreted as a syscall failure because it looks like
a small negative number.
>From David's description of the 2.5 patch (the link above has
the explanation):
Many architectures (alpha, ia64, ppc, ppc64, sparc, and sparc64 at least)
use a syscall convention which provides for a return value and a separate
error flag. On those architectures, it can be beneficial if the kernel
provides a mechanism to signal that a syscall call has completed
successfully, even when the returned value is potentially a (small)
negative number. The patch below provides a hook for such a mechanism via
a macro called force_successful_syscall_return(). On x86, this would be
simply a no-op (because on x86, user-level has to be hacked to handle such
cases).
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] 2.4 force_successful_syscall()
2003-09-17 20:00 ` [PATCH] 2.4 force_successful_syscall() Marcelo Tosatti
2003-09-17 21:41 ` Bjorn Helgaas
@ 2003-09-18 5:42 ` Aneesh Kumar K.V
2003-09-18 6:01 ` Aneesh Kumar K.V
1 sibling, 1 reply; 4+ messages in thread
From: Aneesh Kumar K.V @ 2003-09-18 5:42 UTC (permalink / raw)
To: Marcelo Tosatti
Cc: Helgaas, Bjorn (HP), Marcelo Tosatti, linux-ia64, linux-kernel
On Thu, 2003-09-18 at 01:30, Marcelo Tosatti wrote:
> On Wed, 10 Sep 2003, Bjorn Helgaas wrote:
>
> > Here's a 2.4 backport of this change to 2.5:
> >
> >
> http://linux.bkbits.net:8080/linux-2.5/cset@1.1046.238.7?nav=index.html
> >
> > Alpha, ppc, and sparc64 define force_successful_syscall_return() in
> 2.5,
> > but since it's not obvious to me how to do it correctly in 2.4, I left
> > them unchanged.
>
> Whats the reasoning behing this patch?
IIRC those changes were added to 2.5 by David. Architecture like Ia64
and Alpha support error return via a different register set ( $19 for
Alpha ). But syscalls like ptrace can have negative return value for
successful returns. So in that particular case $19 is forced to be zero
to indicate it is a successful return. IIUC
force_successful_syscall_return is a wrapper around doing that. On
alpha actually r0 in the stack (regs.r0 ) is made zero which is read in
entry.S and put in $19.
-aneesh
^ permalink raw reply [flat|nested] 4+ messages in thread