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<p>cc Alex</p>
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<span>From Alex: It's indeed the kernel restriction and it's a good idea to add a flag to make it configurable.
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<br>
Igor<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> cfe-users <cfe-users-bounces@lists.llvm.org> on behalf of Steven Simpson via cfe-users <cfe-users@lists.llvm.org><br>
<b>Sent:</b> Wednesday, March 22, 2017 9:10 AM<br>
<b>To:</b> cfe-users@lists.llvm.org<br>
<b>Subject:</b> [cfe-users] BPF stack limit</font>
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<div class="PlainText">Hi,<br>
<br>
I'm using Clang to compile C to eBPF, not to run in the Linux kernel, <br>
but in ubpf.<br>
<br>
I occasionally encounter the error "Looks like the BPF stack limit of <br>
512 bytes is exceeded". The limit seems to be hard-wired <br>
(llvm/lib/Target/BPF/BPFRegisterInfo.cpp):<br>
<br>
if (Offset <= -512) {<br>
<br>
(I'm using "clang version 5.0.0 (trunk 294090)" built from SVN source. <br>
Checked it's still there in r298510.)<br>
<br>
Is this an intrinsic limit of eBPF, or just one set by the kernel? If <br>
the latter, and since the kernel isn't the only place BPF could run, <br>
could an option be added to override it? (For the moment, I've just <br>
disabled the check and rebuilt. Plus there are still some changes to <br>
try with my code which might avoid the limit.)<br>
<br>
Thanks,<br>
<br>
Steven<br>
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