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Re: [Qemu-devel] [PATCH] ARM: semi-hosting support for stderr


From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH] ARM: semi-hosting support for stderr
Date: Sun, 14 Nov 2010 17:50:24 +0000

On 19 August 2010 16:11, Christophe Lyon <address@hidden> wrote:
> On 25.06.2010 17:44, Christophe LYON wrote:
>> I propose this small patch so that ARM semi-hosting handles stderr as
>> expected when linking with Newlib/libgloss.

Apologies for this rather belated reply, but I only recently managed
to confirm the relevant information...

Unfortunately there is no means in the semihosting ABI to distinguish
app stdout from stderr. Effectively semihosting defines a single input
channel and a single output channel, not three stdin/stdout/stderr
channels. All the implementations of semihosting that I am aware
of work this way, so it's not just an omission from the semihosting
documentation.

Although newlib/libgloss use different modes for opening stdout
and stderr, the ARM C library implementation does not, for
instance; so your patch is relying on a detail of implementation of
a particular semihosting user. So I don't think we can apply this
patch, because it could break other (nonlibgloss) users of
semihosting.

-- PMM



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