Messages in this thread | | | From | Bjorn Helgaas <> | Subject | Re: [PATCH] 2.4 force_successful_syscall() | Date | Wed, 17 Sep 2003 15:41:16 -0600 |
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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).
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