[PATCH] D61524: [BPF] Support for compile once and run everywhere

[Alexei Starovoitov via Phabricator via llvm-commits]

ast added inline comments.


================
Comment at: lib/Target/BPF/BPFAbstrctMemberAccess.cpp:522
+        Value *SrcAddr = Call->getArgOperand(BpfProbeReadSrcAddrArg);
+        if (transformProbeSrcAddr(M, SrcAddr))
+          Transformed = true;
----------------
yonghong-song wrote:
> ast wrote:
> > does it still need to be limited to bpf_probe_read?
> > Shouldn't new __builtin_preserve_access_index intrinsic allow relocations to be inserted in all possible helpers?
> Yes, the new __builtin_preserve_access_index should make BPF backend does not care about bpf_probe_read at all. The only reason I did here is for debugging. People may miss some relocatable bpf_probe_read. Using +checkoffsetreloc will print out all bpf_probe_read() calls without relocatable bpf_probe_read(). I thought this is a good debugging feature.
> 
> If we do not want to provide this debugging facility, the whole bpf_probe_read() things can be removed.
it seems to be that probe_read check also gating relocation work.
If some other call uses __builtin_preserve_access_index() it will stay un-convereted
and will probably cause compilation failure?

It indeed makes sense to have it for debugging, but probably as a backend flag so that users can catch not only non-relocated probe_read, but other bpf helpers in the future?


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D61524/new/

https://reviews.llvm.org/D61524