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<?xml version="1.0" encoding="UTF-8"?>
<devbook self="archs/ppc/">
<chapter>
<title>Arch specific notes — PPC</title>
<body>
<p>
The Gentoo PowerPC port uses the <c>ppc</c> keyword and maintains compatibility with
all 32 bit PowerPC processors. It is also used for 32 bit userland installs
on 64 bit PowerPC systems.
</p>
</body>
<section>
<title>Common issues</title>
<body>
<p>
Although PowerPC processors can be run in little endian mode, the Linux kernel
runs on PowerPC processors in big endian mode. Due to this fact, a common
PowerPC issue is dealing with code that is written with only little endian
processors in mind (<c>x86</c>/<c>amd64</c>). These bugs can be difficult to find, but are
usually found when loading data from disk (such as a structure written directly
to disk) or during bit operations.
</p>
<p>
The PowerPC port of gcc uses unsigned characters by default, which is
different than on <c>x86</c>. If the code you are working with assumes that the <c>char</c>
type is signed, you can pass <c>-fsigned-char</c> to <c>GCC</c> to work around the issue.
</p>
</body>
</section>
<section>
<title>Altivec</title>
<body>
<p>
Altivec (Apple's name for VMX SIMD instructions) is supported on the <c>G4</c> and <c>G5</c>
processors. You can enable support for the instruction set by passing
<c>-mabi=altivec -maltivec</c> to <c>GCC</c>. Note that passing <c>-mcpu=</c> options may enable
altivec without passing the flags above.
</p>
<p>
Occasionally, an altivec issue that crops up is that Apple uses a different
notation for indicating vectors, (x) instead of {x}. Using something like the
code below to define vectors is the preferred way of fixing this:
</p>
<codesample lang="c">
#ifdef CONFIG_APPLE
#define AVV(x...) (x)
#else
#define AVV(x...) {x}
#endif
</codesample>
</body>
</section>
<section>
<title>Contacting the PowerPC team</title>
<body>
<p>
The PowerPC team can be reached by:
</p>
<ul>
<li>
Via the <c>#gentoo-powerpc</c> IRC channel on Libera.Chat
</li>
<li>
Via email to <c>ppc@gentoo.org</c>
</li>
<li>
Via email to <c>gentoo-ppc-dev@gentoo.org</c> the mailing list
</li>
<li>
Via Bugzilla bugs assigned to <c>ppc@gentoo.org</c>
</li>
</ul>
</body>
</section>
<section>
<title>Other resources</title>
<body>
<ul>
<li>
<uri link="https://wiki.gentoo.org/wiki/PPC/FAQ">Gentoo PPC FAQ</uri>
</li>
<li>
<uri link="https://forums.gentoo.org/viewforum-f-24.html">Gentoo PPC forums</uri>
</li>
</ul>
</body>
</section>
</chapter>
</devbook>
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