<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>On 17 Aug 2012, at 9:00 AM, <a href="mailto:simh-request@trailing-edge.com">simh-request@trailing-edge.com</a> wrote:</div><div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: 'Helvetica Neue'; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="font-family: monospace; ">Well, using the DEC notation for PDP-11 assembler language, @(R0) and <br>(R0) are indeed two different things, and you seem to have understood it <br>perfectly right.<br>Not sure if gas might have its own ideas about notation though...<br></span></span></blockquote></div><div><br></div><div>See the NOTE at the bottom of page 5-5 in Section 5.8, INDEX DEFERRED MODE, in the PDP-11 MACRO-11 Language Reference Manual on the BitSavers web site (<a href="http://www.bitsavers.org/pdf/dec/pdp11/rsx11/RSX11M_V4.1_Apr83/4_ProgramDevelopment/AA-V027A-TC_macro11_Mar83.pdf">http://www.bitsavers.org/pdf/dec/pdp11/rsx11/RSX11M_V4.1_Apr83/4_ProgramDevelopment/AA-V027A-TC_macro11_Mar83.pdf</a>):</div><div><br></div><div> The expression @(ER) may be used, but it</div><div> will be assembled as if it were written</div><div> @0(ER), and a word will be used to store</div><div> the 0.</div><div><br></div><div>GAS has got it wrong. There really is no addressing mode of the form @(ER). GAS should either follow MACRO-11 and convert @(ER) to @0(ER), or it should give an error. It should not convert @(ER) to @ER, which is equivalent to (ER). That is, it should not be silently eliminating the @ deferred address operator from the operand.</div><div><br></div><div>Larry Baker</div><div>US Geological Survey<br>650-329-5608<br><a href="mailto:baker@usgs.gov">baker@usgs.gov</a><br><br></div></body></html>