1 //===- ConcatOutputSection.cpp --------------------------------------------===//
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
29   assert(input->parent == this);  in addInput()
31     align = input->align;  in addInput()
32     flags = input->getFlags();  in addInput()
34     align = std::max(align, input->align);  in addInput()
40 // Branch-range extension can be implemented in two ways, either through ...
42 // (1) Branch islands: Single branch instructions (also of limited range),
44 //     destination. On ARM64, as 16 branch islands are needed to hop between
45 //     opposite ends of a 2 GiB program. LD64 uses branch islands exclusively,
49 //     register, followed by a register-indirect branch. Thunks are
57 // implement thunks. TODO: Adding support for branch islands!
59 // Internally -- as expressed in LLD's data structures -- a
60 // branch-range-extension thunk consists of:
65 // (3.1) new data for the instructions to load & branch to the far address +
70 // Nearly-optimal thunk-placement algorithm features:
74 // * Accounts for the exact space overhead of thunks - no heuristics
76 // * Exploits the full range of call instructions - forward & backward
111 //   is placed, it and all previous input-section addresses are final.
119 // Determine whether we need thunks, which depends on the target arch -- RISC
120 // (i.e., ARM) generally does because it has limited-range branch/call
122 // thunks for programs so large that branch source & destination addresses
123 // might differ more than the range of branch instruction(s).
125   if (!target->usesThunks())  in needsThunks()
129     isecAddr = alignToPowerOf2(isecAddr, isec->align) + isec->getSize();  in needsThunks()
130   if (isecAddr - addr + in.stubs->getSize() <=  in needsThunks()
131       std::min(target->backwardBranchRange, target->forwardBranchRange))  in needsThunks()
135     for (Reloc &r : isec->relocs) {  in needsThunks()
136       if (!target->hasAttr(r.type, RelocAttrBits::BRANCH))  in needsThunks()
139       // Pre-populate the thunkMap and memoize call site counts for every  in needsThunks()
147       // We can avoid work on InputSections that have no BRANCH relocs.  in needsThunks()
148       isec->hasCallSites = true;  in needsThunks()
155 // beyond which stubs are within range of a simple forward branch.
164     // currently-active section get finalized, and all input sections are  in estimateStubsInRangeVA()
171   uint64_t isecVA = inputs[callIdx]->getVA();  in estimateStubsInRangeVA()
175     isecEnd = alignToPowerOf2(isecEnd, isec->align) + isec->getSize();  in estimateStubsInRangeVA()
179   uint64_t forwardBranchRange = target->forwardBranchRange;  in estimateStubsInRangeVA()
182   assert(isecEnd - isecVA <= forwardBranchRange &&  in estimateStubsInRangeVA()
184   uint64_t stubsInRangeVA = isecEnd + maxPotentialThunks * target->thunkSize +  in estimateStubsInRangeVA()
185                             in.stubs->getSize() - forwardBranchRange;  in estimateStubsInRangeVA()
188       ", stubs = " + std::to_string(in.stubs->getSize()) + ", isecVA = " +  in estimateStubsInRangeVA()
191       ", tail = " + utohexstr(isecEnd - isecVA) +  in estimateStubsInRangeVA()
192       ", slop = " + utohexstr(forwardBranchRange - (isecEnd - isecVA)));  in estimateStubsInRangeVA()
197   size = alignToPowerOf2(size, isec->align);  in finalizeOne()
198   fileSize = alignToPowerOf2(fileSize, isec->align);  in finalizeOne()
199   isec->outSecOff = size;  in finalizeOne()
200   isec->isFinal = true;  in finalizeOne()
201   size += isec->getSize();  in finalizeOne()
202   fileSize += isec->getFileSize();  in finalizeOne()
217   uint64_t forwardBranchRange = target->forwardBranchRange;  in finalize()
218   uint64_t backwardBranchRange = target->backwardBranchRange;  in finalize()
220   size_t thunkSize = target->thunkSize;  in finalize()
229   // addr + size is the start address of the first non-finalized section.  in finalize()
231   // inputs[finalIdx] is for finalization (address-assignment)  in finalize()
233   // Kick-off by ensuring that the first input section has an address  in finalize()
239     assert(isec->isFinal);  in finalize()
240     uint64_t isecVA = isec->getVA();  in finalize()
242     // Assign addresses up-to the forward branch-range limit.  in finalize()
245     // (on Arm64: 12). If a section starts with a branch instruction and  in finalize()
246     // contains several branch instructions in succession, then the distance  in finalize()
252           alignToPowerOf2(addr + size, inputs[finalIdx]->align) +  in finalize()
253           inputs[finalIdx]->getSize();  in finalize()
254       if (expectedNewSize >= isecVA + forwardBranchRange - slop)  in finalize()
259     if (!isec->hasCallSites)  in finalize()
266       // reach any stub with a forward branch. Note that although it  in finalize()
270       // (and start of __stubs) comes within range of a forward branch.  in finalize()
274     std::vector<Reloc> &relocs = isec->relocs;  in finalize()
276     // `-r` mode.  in finalize()
281       if (!target->hasAttr(r.type, RelocAttrBits::BRANCH))  in finalize()
284       // Calculate branch reachability boundaries  in finalize()
287           backwardBranchRange < callVA ? callVA - backwardBranchRange : 0;  in finalize()
293       if (funcSym->isInStubs() && callVA >= stubsInRangeVA) {  in finalize()
296         // are now within range of a simple forward branch.  in finalize()
299       uint64_t funcVA = funcSym->resolveBranchVA();  in finalize()
309         uint64_t thunkVA = thunkInfo.isec->getVA();  in finalize()
317         // There were too many consecutive branch instructions for `slop`  in finalize()
324           makeSyntheticInputSection(isec->getSegName(), isec->getName());  in finalize()
325       thunkInfo.isec->parent = this;  in finalize()
326       assert(thunkInfo.isec->live);  in finalize()
328       StringRef thunkName = saver().save(funcSym->getName() + ".thunk." +  in finalize()
330       if (!isa<Defined>(funcSym) || cast<Defined>(funcSym)->isExternal()) {  in finalize()
331         r.referent = thunkInfo.sym = symtab->addDefined(  in finalize()
343       thunkInfo.sym->used = true;  in finalize()
344       target->populateThunk(thunkInfo.isec, funcSym);  in finalize()
351   log("thunks for " + parent->name + "," + name +  in finalize()
361     isec->writeTo(buf + isec->outSecOff);  in writeTo()
369     while (i < ie && (t == te || inputs[i]->empty() ||  in writeTo()
370                       inputs[i]->outSecOff < thunks[t]->outSecOff)) {  in writeTo()
371       inputs[i]->writeTo(buf + inputs[i]->outSecOff);  in writeTo()
374     while (t < te && (i == ie || thunks[t]->outSecOff < inputs[i]->outSecOff)) {  in writeTo()
375       thunks[t]->writeTo(buf + thunks[t]->outSecOff);  in writeTo()
382   switch (sectionType(input->getFlags())) {  in finalizeFlags()
383   default /*type-unspec'ed*/:  in finalizeFlags()
400     flags |= input->getFlags();  in finalizeFlags()
407   NamePair names = maybeRenameSection({isec->getSegName(), isec->getName()});  in getOrCreateForInput()
410     if (isec->getSegName() == segment_names::text &&  in getOrCreateForInput()
411         isec->getName() != section_names::gccExceptTab &&  in getOrCreateForInput()
412         isec->getName() != section_names::ehFrame)  in getOrCreateForInput()
421   auto newNames = config->sectionRenameMap.find(key);  in maybeRenameSection()
422   if (newNames != config->sectionRenameMap.end())  in maybeRenameSection()
423     return newNames->second;  in maybeRenameSection()