One step of converting the various data structures in xpt_struct.h into being statically allocated is to mark them const. Fortunately, almost all of the users of these data structures already pretend they are const. The bulk of the changes are to the deserialization code in xpt_struct.cpp: for the various arrays the code reads in, it has to be written into a local temp array, then that array gets assigned into the const field in the real XPT data structure. There's no particular reason this can't land early, but it is a little finicky so I won't put my patches up for review until I'm more sure about the viability of bug 1438688.

This has been stable, so I might as well land it. I don't think it is too invasive. This is probably more patches than are really necessary.

Comment on attachment 8955268 [details] Bug 1442363, part 1 - Constify RegisterXPTHeader(). https://reviewboard.mozilla.org/r/224408/#review231812

Comment on attachment 8955269 [details] Bug 1442363, part 2 - Constify XPTHeader::interface_directory. https://reviewboard.mozilla.org/r/224410/#review231814 ::: xpcom/typelib/xpt/xpt_struct.cpp:149 (Diff revision 3) > if (!XPT_Do32(cursor, &data_pool)) > return false; > > XPT_SetDataOffset(cursor->state, data_pool); > > + XPTInterfaceDirectoryEntry* interface_directory = nullptr; I can't work out why you introduced the local variable, but presumably it's necessary.

Comment on attachment 8955270 [details] Bug 1442363, part 3 - Constify the strings in xpt_struct.h. https://reviewboard.mozilla.org/r/224412/#review231816

Comment on attachment 8955271 [details] Bug 1442363, part 4 - Constify XPTInterfaceDirectoryEntry::interface_descriptor. https://reviewboard.mozilla.org/r/224414/#review231818

Comment on attachment 8955272 [details] Bug 1442363, part 5 - Constify XPTInterfaceDescriptor::method_descriptors. https://reviewboard.mozilla.org/r/224416/#review231820 ::: xpcom/reflect/xptinfo/xptiInterfaceInfo.cpp:88 (Diff revision 3) > mParent = parent; > if (parent->GetHasNotXPCOMFlag()) { > SetHasNotXPCOMFlag(); > } else { > for (uint16_t idx = 0; idx < mDescriptor->num_methods; ++idx) { > - nsXPTMethodInfo* method = reinterpret_cast<nsXPTMethodInfo*>( > + const nsXPTMethodInfo* method = reinterpret_cast<const nsXPTMethodInfo*>( Can this be a static_cast? nsXPTMethodInfo is a subclass of XPTMethodDescriptor. ::: xpcom/reflect/xptinfo/xptiInterfaceInfo.cpp:193 (Diff revision 3) > *info = nullptr; > return NS_ERROR_INVALID_ARG; > } > > // else... > - *info = reinterpret_cast<nsXPTMethodInfo*> > + *info = reinterpret_cast<const nsXPTMethodInfo*> ditto ::: xpcom/reflect/xptinfo/xptiInterfaceInfo.cpp:209 (Diff revision 3) > > // This is a slow algorithm, but this is not expected to be called much. > for(uint16_t i = 0; i < mDescriptor->num_methods; ++i) > { > const nsXPTMethodInfo* info; > - info = reinterpret_cast<nsXPTMethodInfo*> > + info = reinterpret_cast<const nsXPTMethodInfo*> ditto

Comment on attachment 8955273 [details] Bug 1442363, part 6 - Constify XPTInterfaceDescriptor::const_descriptors. https://reviewboard.mozilla.org/r/224418/#review231822

Comment on attachment 8955274 [details] Bug 1442363, part 7 - Constify XPTInterfaceDescriptor::additional_types. https://reviewboard.mozilla.org/r/224420/#review231826

Comment on attachment 8955275 [details] Bug 1442363, part 8 - Constify XPTMethodDescriptor::params. https://reviewboard.mozilla.org/r/224422/#review231828

(In reply to Nicholas Nethercote [:njn] from comment #27) > I can't work out why you introduced the local variable, but presumably it's > necessary. My changes make the array member const, so individual elements of the array member can't be overwritten. But we need to overwrite them to initialize the array. I introduce a local variable that is non-const, so I can write to it. Then, once I'm done initializing it, I can assign that array to the const one in the struct. (In reply to Nicholas Nethercote [:njn] from comment #30) > Can this be a static_cast? nsXPTMethodInfo is a subclass of > XPTMethodDescriptor. Yeah, I was kind of wondering that myself. I'll fix the cast (unless somehow it doesn't work).

Pushed by amccreight@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/031309abee2c part 1 - Constify RegisterXPTHeader(). r=njn https://hg.mozilla.org/integration/autoland/rev/6b7e0ca809e9 part 2 - Constify XPTHeader::interface_directory. r=njn https://hg.mozilla.org/integration/autoland/rev/ae8424c2ac77 part 3 - Constify the strings in xpt_struct.h. r=njn https://hg.mozilla.org/integration/autoland/rev/4a4ea07f6467 part 4 - Constify XPTInterfaceDirectoryEntry::interface_descriptor. r=njn https://hg.mozilla.org/integration/autoland/rev/05a7101669f8 part 5 - Constify XPTInterfaceDescriptor::method_descriptors. r=njn https://hg.mozilla.org/integration/autoland/rev/9cec783aa764 part 6 - Constify XPTInterfaceDescriptor::const_descriptors. r=njn https://hg.mozilla.org/integration/autoland/rev/d65876d7d615 part 7 - Constify XPTInterfaceDescriptor::additional_types. r=njn https://hg.mozilla.org/integration/autoland/rev/e702856c3ec6 part 8 - Constify XPTMethodDescriptor::params. r=njn

https://hg.mozilla.org/mozilla-central/rev/031309abee2c https://hg.mozilla.org/mozilla-central/rev/6b7e0ca809e9 https://hg.mozilla.org/mozilla-central/rev/ae8424c2ac77 https://hg.mozilla.org/mozilla-central/rev/4a4ea07f6467 https://hg.mozilla.org/mozilla-central/rev/05a7101669f8 https://hg.mozilla.org/mozilla-central/rev/9cec783aa764 https://hg.mozilla.org/mozilla-central/rev/d65876d7d615 https://hg.mozilla.org/mozilla-central/rev/e702856c3ec6