<div dir="ltr">For completeness, the default behavior is in ARMSubtarget.cpp:<div><span style="font-family:arial,sans-serif;font-size:13px"> // Assume pre-ARMv6 doesn't support </span><span class="" style="font-family:arial,sans-serif;font-size:13px">unaligned</span><span style="font-family:arial,sans-serif;font-size:13px"> accesses.</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> //</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px"> // ARMv6 may or may not support </span><span class="" style="font-family:arial,sans-serif;font-size:13px">unaligned</span><span style="font-family:arial,sans-serif;font-size:13px"> accesses depending on the</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> // SCTLR.U bit, which is architecture-specific. We assume ARMv6</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px"> // Darwin targets support </span><span class="" style="font-family:arial,sans-serif;font-size:13px">unaligned</span><span style="font-family:arial,sans-serif;font-size:13px"> accesses, and others don't.</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> //</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px"> // ARMv7 always has SCTLR.U set to 1, but it has a new SCTLR.A bit</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> // which raises an alignment fault on </span><span class="" style="font-family:arial,sans-serif;font-size:13px">unaligned</span><span style="font-family:arial,sans-serif;font-size:13px"> accesses. Linux</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> // defaults this bit to 0 and handles it as a system-wide (not</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px"> // per-process) setting. It is therefore safe to assume that ARMv7+</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> // Linux targets support </span><span class="" style="font-family:arial,sans-serif;font-size:13px">unaligned</span><span style="font-family:arial,sans-serif;font-size:13px"> accesses. The same goes for NaCl.</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px"> //</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px"> // The above behavior is consistent with GCC.</span><br>
</div><div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">The change lgtm.</span></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">
On Sun, Aug 18, 2013 at 6:15 AM, Renato Golin <span dir="ltr"><<a href="mailto:renato.golin@linaro.org" target="_blank">renato.golin@linaro.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><div class="im">On 18 August 2013 08:17, Jeroen Hofstee <span dir="ltr"><<a href="mailto:clang@myspectrum.nl" target="_blank">clang@myspectrum.nl</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">If I make -munaligned-access a dummy (at least that what<br>
I guess you mean), there is no proper way to allow unaligned<br>
accesses on say one of the BSDs or e.g. armv6 and linux.<br>
Both flags are needed to control alignment behaviour in general.<br></blockquote><div></div></div><br></div></div><div class="gmail_extra">Good point. LGTM.</div><span class="HOEnZb"><font color="#888888"><div class="gmail_extra">
<br></div><div class="gmail_extra">--renato</div>
</font></span></div>
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