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Date:	Sun, 14 Apr 2024 16:26:27 +0300
Message-Id:	<86jzl0m5x8.fsf@gnu.org>
From:	"Eli Zaretskii (eliz AT gnu DOT org) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
To:	Pali <pali AT pali DOT im>
Cc:	dj AT delorie DOT com, sezeroz AT gmail DOT com, djgpp AT delorie DOT com
In-Reply-To:	<20240414121034.h34pjed3s3udathh@pali> (message from Pali on Sun,
	14 Apr 2024 14:10:34 +0200)
Subject:	Re: Error handling in __djgpp_set_page_attributes()
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> Date: Sun, 14 Apr 2024 14:10:34 +0200
> From: Pali <pali AT pali DOT im>
> Cc: dj AT delorie DOT com, sezeroz AT gmail DOT com, djgpp AT delorie DOT com
> 
> On Sunday 14 April 2024 14:46:02 Eli Zaretskii wrote:
> > > Date: Sun, 14 Apr 2024 12:42:51 +0200
> > > From: Pali <pali AT pali DOT im>
> > > Cc: dj AT delorie DOT com, sezeroz AT gmail DOT com, djgpp AT delorie DOT com
> > > 
> > > What I think is important: include information that out_addr/num_bytes
> > > address range must belong to sbrk allocator. This is something hard to
> > > figure out without reading the source code of the function.
> > 
> > What other allocator there can be in DJGPP?  I thought all allocations
> > go through sbrk, isn't that so?
> 
> __djgpp_set_page_attributes function takes our_addr argument and it was
> not clear for me what it is. Current documentation refers to the DPMI
> 0507H function, which takes memory handle and offset in it, which
> describes linear memory. __djgpp_set_page_attributes on the other hand
> expects for that out_addr is the offset in the DS segment and is doing
> translation to memory handle + offset by looking into sbrk allocator
> (via _djgpp_memory_handle).

So I think it's important to say that the OUT_ADDR is the offset from
the DS segment base, and use 'sbrk' and 'malloc' as examples of
functions that return such addresses, in contrast to
__dpmi_allocate_linear_memory and similar APIs.  IOW, say that offsets
from DS are the requirement, and use 'sbrk' etc. as examples of
satisfying the requirement.  The fact that __djgpp_set_page_attributes
translates to linear addresses is also worth mentioning.

> Important is that it is from allocator (not from any other source).

AFAIU, this is not a requirement.  For example, if I know that offset
0x1000 from DS belongs to the program's address space (as it usually
is), I can use that as OUT_ADDR.  Right?

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