This is the mail archive of the
libffi-discuss@sourceware.org
mailing list for the libffi project.
Re: libffi: Simplify PowerPC assembly and avoid CPU-specific string instructions
- From: "Moffett, Kyle D" <Kyle dot D dot Moffett at boeing dot com>
- To: "647288 at bugs dot debian dot org" <647288 at bugs dot debian dot org>
- Cc: Anthony Green <green at moxielogic dot com>, "libffi-discuss at sourceware dot org" <libffi-discuss at sourceware dot org>
- Date: Tue, 1 Nov 2011 15:55:18 -0500
- Subject: Re: libffi: Simplify PowerPC assembly and avoid CPU-specific string instructions
- References: <20111101155343.30222.16020.reportbug@eternium.exmeritus.com>
On Nov 01, 2011, at 11:53, Kyle Moffett wrote:
> After upgrading to a new version of GNU ld for PowerPC e500, I started
> seeing build errors on e500 systems again. It turns out that the
> PowerPC "string instructions" are unimplemented on PPC440 and most other
> embedded cores, and also cause unexpectedly high instruction latencies
> and pipeline stalls even on POWER processors.
>
> This historically worked in the past because the unknown string opcodes
> are trapped on PPC440 and similar systems and emulated in the kernel,
> though that is obviously very inefficient and undesirable.
>
> Since the struct-copy code doesn't really need to be implemented in
> assembly, this patch ensures that there is always enough space to store
> both r3 and r4 and then uses C to extract the 1-8 byte "small struct"
> into the user-provided memory.
>
> Even with all the big new comments, it's still removes 11 lines of code,
> and the ASM is much simpler and easier to understand now.
>
> Please consider applying.
Oh, I forgot to mention the testing I did on this patch:
I have applied this patch on top of the previous PowerPC SPE patches
(Debian version 3.0.10-3) and it builds, passes the testsuite, and
correctly installs on powerpc, powerpc64, and e500v2.
NOTE: The e500v2 testsuite does have one unrelated failure with GCC-4.6
even with this patch due to GCC PR target/50906:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50906
Cheers,
Kyle Moffett
--
Curious about my work on the Debian powerpcspe port?
I'm keeping a blog here: http://pureperl.blogspot.com/