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</o:shapelayout></xml><![endif]--></head><body lang=EN-IE link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;mso-fareast-language:EN-US'>With Gnu this is handled by the FILL command or using the ‘</span><span style='font-family:"Courier New";mso-fareast-language:EN-US'>=N</span><span style='font-family:"Book Antiqua",serif;mso-fareast-language:EN-US'>’ expression. For example:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";mso-fareast-language:EN-US'>SECTIONS {<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";mso-fareast-language:EN-US'> .text : { *(.text) *(.text.*) } = 0xCC<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";mso-fareast-language:EN-US'>}<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;mso-fareast-language:EN-US'>I must admit, I haven’t yet used LLD, but I would have expected that it would be functionally equivalent to Gnu ld?<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;mso-fareast-language:EN-US'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org] <b>On Behalf Of </b>James Henderson via llvm-dev<br><b>Sent:</b> 10 March 2017 16:19<br><b>To:</b> llvm-dev@lists.llvm.org<br><b>Subject:</b> [llvm-dev] [ELF] [RFC] Padding between executable sections<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'>Hi,<o:p></o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'>I was doing some experiments with LLD and noticed that it pads out OutputSections with null bytes in all cases (as far as I could tell). However, for executable sections on some targets, 0x00 forms part of an executable instruction that is not nop. In particular, for x86_64 targets at least, the sequence 0x00 0x00 is an add instruction. This can result in confusing disassembly.<o:p></o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'>For example, on x86_64, given a simple InputSection that is a single "0xc3 retq" instruction, and given an alignment of 16 bytes, 15 null bytes are inserted between the end of that InputSection and the next. In the disassembly I then see the retq instruction followed by a series of adds, the last of which actually consumes 1 or more bytes of the next section to form a valid instruction, which can in turn throw off the disassembly of the following instructions at the start of the next section.<br><br>What do people think about using a target-specific nop instruction sequence to pad executable sections? Another possible option, on x86_64 at least (I haven't investigated other targets), is to use the 0xcc interrupt instruction.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'>Regards,<o:p></o:p></p></div><div><p class=MsoNormal>James<o:p></o:p></p></div></div></div></body></html>