[PATCH] D155535: [WebAssembly][Objcopy] Write output section headers identically to inputs

[Thomas Lively via Phabricator via llvm-commits]

tlively added inline comments.


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Comment at: llvm/lib/ObjectYAML/WasmEmitter.cpp:650
+    unsigned HeaderSecSizeEncodingLen =
+        Sec->HeaderSecSizeEncodingLen ? *Sec->HeaderSecSizeEncodingLen : 0;
+    if (HeaderSecSizeEncodingLen < getULEB128Size(OutString.size())) {
----------------
jhenderson wrote:
> aheejin wrote:
> > I think this is why the tests are failing. Will fix that.
> Thanks, I agree the previous version looks suspicious. This number controls the default encoding length, so 5 seems appropriate.
> 
> Looking at this again, I think there is one technical bug here still though, in that if OutString happened to be so long that the LEB had to be 6 bytes or longer, then the user would be forced to specify the YAML field, even if it was just to the same size as the expected LEB. Perhaps worth changing 5 to something like `std::max(5, getULEB128Size(OutString.size())`? (Probably factor out the size calculation into a local variable)
It's not possible for the size to require greater than 5 bytes because it is an unsigned 32-bit value. Each byte of a LEB has 7 significant bits and ceil(32/7) = 5. Indeed the Wasm spec does not allow using LEBs larger than 5 bytes to encode 32-bit values.


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155535/new/

https://reviews.llvm.org/D155535