<div dir="ltr"><div dir="ltr"><div dir="ltr"><div><div dir="ltr" class="gmail_signature">On Tue, Apr 2, 2019 at 3:49 PM Brian Cain via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<br></div></div></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div lang="EN-US"><div class="gmail-m_-8843592839475115924WordSection1"><p class="MsoNormal" style="text-indent:0.5in">This is the intended design of GNU ld. Some linkers follow this behavior, some don’t. e.g. IIRC lld chose to have an implicit grouping (like ld’s start-group/end-group), which comes w/pros and cons. Pros: like you said, you needn’t concern yourself with the order of the libs. If you are consuming several different libraries, one could see the perspective that from up here at the executable’s perspective, you don’t care how the linker does symbol resolution and one could imagine that it might not even matter that it takes more time for it to go and search the ones that appear earlier on the command line. Cons: increased link time, cyclical dependencies among libraries are easy to introduce now because the linker won’t alert you to the problem.</p></div></div></blockquote><div><br></div><div>This doesn't really have an impact on link times in lld (note that lld is faster than both gnu ld and gold). This is because lld just adds all symbols to its internal symbol table, but unresolved archive symbols get added as lazy symbols that don't show up in the output unless they are actually referenced. It's slower in other linkers because they do another full iteration over the symbol table every time an archive is visited. The biggest issue I saw with this is that you actually have different semantics for what gets linked, but it turned out that every case where this broke the link was really a bug in the program being linked, often duplicate definitions of stuff.</div><div><br></div><div>- Michael Spencer<br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div lang="EN-US"><div class="gmail-m_-8843592839475115924WordSection1"><p class="MsoNormal" style="text-indent:0.5in"><u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Relevant details from the ld.bfd manpage:<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal" style="margin-left:0.5in">--start-group archives --end-group<u></u><u></u></p><p class="MsoNormal" style="margin-left:0.5in"><u></u> <u></u></p><p class="MsoNormal" style="margin-left:0.5in">…<u></u><u></u></p><p class="MsoNormal" style="margin-left:0.5in">The specified archives are searched repeatedly until no new undefined references are created. <i>Normally, an archive is searched only once in the order that it is specified on the command line. If a symbol in that archive is needed to resolve an undefined symbol referred to by an object in an archive that appears later on the command line, the linker would not be able to resolve that reference.</i> By grouping the archives, they all be searched repeatedly until all possible references are resolved.<u></u><u></u></p><p class="MsoNormal" style="margin-left:0.5in">Using this option has a significant performance cost. It is best to use it only when there are unavoidable circular references between two or more archives.<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><div style="border-style:none none none solid;border-left-width:1.5pt;border-left-color:blue;padding:0in 0in 0in 4pt"><div><div style="border-style:solid none none;border-top-width:1pt;border-top-color:rgb(225,225,225);padding:3pt 0in 0in"><p class="MsoNormal" style="margin-left:5.5pt"><b>From:</b> libcxx-dev <<a href="mailto:libcxx-dev-bounces@lists.llvm.org" target="_blank">libcxx-dev-bounces@lists.llvm.org</a>> <b>On Behalf Of </b>Louis Dionne via libcxx-dev<br><br><b><u></u><u></u></b></p></div></div><div><p class="MsoNormal">To clarify, what I meant is that from a very naive point of view, the order in which you provide `-l`'s on the command line shouldn't matter -- it should work as long as you provide the right set of `-l`'s. I'm puzzled every time a tool (e.g. `ld`) behaves differently based on the order of command line arguments.<u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Maybe there's a good reason for this, though. Maybe the cfe-dev folks can explain?<u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Louis<u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p></div></div></div></div>_______________________________________________<br>
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