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<p class="MsoNormal">In verifying AArch64/ILP32 on hardware I ran across quite a few alignment issues,<o:p></o:p></p>
<p class="MsoNormal">some of which were caused by the use of SUBALIGN() in the linker scripts mentioned here:<o:p></o:p></p>
<p class="MsoNormal"><a href="https://devel.rtems.org/ticket/4178">https://devel.rtems.org/ticket/4178</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">SUBALIGN() was necessary for two reasons:<o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">libc sysinit linker sets (this can be fixed in the sysinit handler struct)<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">splinkersets01 could not be made to pass on ILP32 as-is without SUBALIGN<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">It seems that splinkersets01 makes the assumption that linker sets are aligned to no more<o:p></o:p></p>
<p class="MsoNormal">than the size of a pointer. For ILP32, this is not the case since AArch64 hardware is very<o:p></o:p></p>
<p class="MsoNormal">sensitive to misaligned accesses and many structs in linker sections need to be aligned to<o:p></o:p></p>
<p class="MsoNormal">8-byte boundaries to avoid throwing exceptions. Some may even need to be aligned to<o:p></o:p></p>
<p class="MsoNormal">16-byte boundaries depending on the structure, but this doesn’t apply to splinkersets01.<o:p></o:p></p>
<p class="MsoNormal">The resultant alignment padding causes many assertions in splinkersets01 to fail.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m trying to find a way to make everything work together, but I’d like some input.<o:p></o:p></p>
<p class="MsoNormal">The highlights with ILP32/LibBSD/hardware:<o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">current codebase: stuffs a struct into a linker section with bad alignment and throws an exception<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">drop SUBALIGN and fix the sysinit issue: splinkersets01 fails, all other tests pass, code runs<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Paths forward:<o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">disable splinkersets01 for AArch64/ILP32 BSPs<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">attempt to detect section alignment and adjust splinkersets01 as necessary<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">splitting the section up for different alignments would require touching every linker script<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">?<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hopefully I’m just missing something.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Kinsey<o:p></o:p></p>
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