1//===------------------------------------------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLD_ELF_RELOCSCAN_H
10#define LLD_ELF_RELOCSCAN_H
11
12#include "Config.h"
13#include "InputFiles.h"
14#include "InputSection.h"
15#include "Relocations.h"
16#include "SyntheticSections.h"
17#include "Target.h"
18
19using namespace llvm;
20using namespace llvm::ELF;
21using namespace llvm::object;
22
23namespace lld::elf {
24
25// Build a bitmask with one bit set for each 64 subset of RelExpr.
26inline constexpr uint64_t buildMask() { return 0; }
27
28template <typename... Tails>
29inline constexpr uint64_t buildMask(int head, Tails... tails) {
30 return (0 <= head && head < 64 ? uint64_t(1) << head : 0) |
31 buildMask(tails...);
32}
33
34// Return true if `Expr` is one of `Exprs`.
35// There are more than 64 but less than 128 RelExprs, so we divide the set of
36// exprs into [0, 64) and [64, 128) and represent each range as a constant
37// 64-bit mask. Then we decide which mask to test depending on the value of
38// expr and use a simple shift and bitwise-and to test for membership.
39template <RelExpr... Exprs> bool oneof(RelExpr expr) {
40 assert(0 <= expr && (int)expr < 128 &&
41 "RelExpr is too large for 128-bit mask!");
42
43 if (expr >= 64)
44 return (uint64_t(1) << (expr - 64)) & buildMask((Exprs - 64)...);
45 return (uint64_t(1) << expr) & buildMask(Exprs...);
46}
47
48// This class encapsulates states needed to scan relocations for one
49// InputSectionBase.
50class RelocScan {
51public:
52 Ctx &ctx;
53 InputSectionBase *sec;
54
55 RelocScan(Ctx &ctx, InputSectionBase *sec = nullptr) : ctx(ctx), sec(sec) {}
56 template <class ELFT, class RelTy>
57 void scan(typename Relocs<RelTy>::const_iterator &i, RelType type,
58 int64_t addend);
59 void scanEhSection(EhInputSection &s);
60
61 template <class ELFT, class RelTy>
62 int64_t getAddend(const RelTy &r, RelType type);
63 bool maybeReportUndefined(Undefined &sym, uint64_t offset);
64 bool checkTlsLe(uint64_t offset, Symbol &sym, RelType type);
65 bool isStaticLinkTimeConstant(RelExpr e, RelType type, const Symbol &sym,
66 uint64_t relOff) const;
67 void process(RelExpr expr, RelType type, uint64_t offset, Symbol &sym,
68 int64_t addend) const;
69 // Process relocation after needsGot/needsPlt flags are already handled.
70 void processAux(RelExpr expr, RelType type, uint64_t offset, Symbol &sym,
71 int64_t addend) const;
72 unsigned handleTlsRelocation(RelExpr expr, RelType type, uint64_t offset,
73 Symbol &sym, int64_t addend);
74
75 // Process R_PC relocations. These are the most common relocation type, so we
76 // inline the isStaticLinkTimeConstant check.
77 void processR_PC(RelType type, uint64_t offset, int64_t addend, Symbol &sym) {
78 if (LLVM_UNLIKELY(sym.isGnuIFunc()))
79 sym.setFlags(HAS_DIRECT_RELOC);
80 if (sym.isPreemptible || (isAbsolute(sym) && ctx.arg.isPic))
81 processAux(expr: R_PC, type, offset, sym, addend);
82 else
83 sec->addReloc(r: {.expr: R_PC, .type: type, .offset: offset, .addend: addend, .sym: &sym});
84 }
85
86 // Process R_PLT_PC relocations. These are very common (calls), so we inline
87 // the isStaticLinkTimeConstant check. Non-preemptible symbols are optimized
88 // to R_PC (direct call).
89 void processR_PLT_PC(RelType type, uint64_t offset, int64_t addend,
90 Symbol &sym) {
91 if (LLVM_UNLIKELY(sym.isGnuIFunc())) {
92 process(expr: R_PLT_PC, type, offset, sym, addend);
93 return;
94 }
95 if (sym.isPreemptible) {
96 sym.setFlags(NEEDS_PLT);
97 sec->addReloc(r: {.expr: R_PLT_PC, .type: type, .offset: offset, .addend: addend, .sym: &sym});
98 } else if (!(isAbsolute(sym) && ctx.arg.isPic)) {
99 sec->addReloc(r: {.expr: R_PC, .type: type, .offset: offset, .addend: addend, .sym: &sym});
100 } else {
101 processAux(expr: R_PC, type, offset, sym, addend);
102 }
103 }
104
105 // Handle TLS Initial-Exec relocation.
106 template <bool enableIeToLe = true>
107 void handleTlsIe(RelExpr ieExpr, RelType type, uint64_t offset,
108 int64_t addend, Symbol &sym) {
109 if (enableIeToLe && !ctx.arg.shared && !sym.isPreemptible) {
110 // Optimize to Local Exec.
111 sec->addReloc(r: {.expr: R_TPREL, .type: type, .offset: offset, .addend: addend, .sym: &sym});
112 } else {
113 sym.setFlags(NEEDS_TLSIE);
114 // R_GOT (absolute GOT address) needs a RELATIVE dynamic relocation in
115 // PIC when the relocation uses the full address (not just low page bits).
116 if (ieExpr == R_GOT && ctx.arg.isPic &&
117 !ctx.target->usesOnlyLowPageBits(type))
118 sec->getPartition(ctx).relaDyn->addRelativeReloc(
119 dynType: ctx.target->relativeRel, isec&: *sec, offsetInSec: offset, sym, addend, addendRelType: type, expr: ieExpr);
120 else
121 sec->addReloc(r: {.expr: ieExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
122 }
123 }
124
125 // Handle TLS Local-Dynamic relocation. Returns true if the __tls_get_addr
126 // call should be skipped (i.e., caller should ++it).
127 bool handleTlsLd(RelExpr sharedExpr, RelType type, uint64_t offset,
128 int64_t addend, Symbol &sym) {
129 if (ctx.arg.shared) {
130 ctx.needsTlsLd.store(i: true, m: std::memory_order_relaxed);
131 sec->addReloc(r: {.expr: sharedExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
132 return false;
133 }
134 // Optimize to Local Exec.
135 sec->addReloc(r: {.expr: R_TPREL, .type: type, .offset: offset, .addend: addend, .sym: &sym});
136 return true;
137 }
138
139 // Handle TLS General-Dynamic relocation. Returns true if the __tls_get_addr
140 // call should be skipped (i.e., caller should ++it).
141 bool handleTlsGd(RelExpr sharedExpr, RelExpr ieExpr, RelExpr leExpr,
142 RelType type, uint64_t offset, int64_t addend, Symbol &sym) {
143 if (ctx.arg.shared) {
144 sym.setFlags(NEEDS_TLSGD);
145 sec->addReloc(r: {.expr: sharedExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
146 return false;
147 }
148 if (sym.isPreemptible) {
149 // Optimize to Initial Exec.
150 sym.setFlags(NEEDS_TLSIE);
151 sec->addReloc(r: {.expr: ieExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
152 } else {
153 // Optimize to Local Exec.
154 sec->addReloc(r: {.expr: leExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
155 }
156 return true;
157 }
158
159 // Handle TLSDESC relocation.
160 void handleTlsDesc(RelExpr sharedExpr, RelExpr ieExpr, RelType type,
161 uint64_t offset, int64_t addend, Symbol &sym) {
162 if (ctx.arg.shared) {
163 // NEEDS_TLSDESC_NONAUTH is a no-op for non-AArch64 targets and detects
164 // incompatibility with NEEDS_TLSDESC_AUTH.
165 sym.setFlags(NEEDS_TLSDESC | NEEDS_TLSDESC_NONAUTH);
166 sec->addReloc(r: {.expr: sharedExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
167 } else if (sym.isPreemptible) {
168 // Optimize to Initial Exec.
169 sym.setFlags(NEEDS_TLSIE);
170 sec->addReloc(r: {.expr: ieExpr, .type: type, .offset: offset, .addend: addend, .sym: &sym});
171 } else {
172 // Optimize to Local Exec.
173 sec->addReloc(r: {.expr: R_TPREL, .type: type, .offset: offset, .addend: addend, .sym: &sym});
174 }
175 }
176};
177
178template <class ELFT, class RelTy>
179int64_t RelocScan::getAddend(const RelTy &r, RelType type) {
180 return RelTy::HasAddend ? elf::getAddend<ELFT>(r)
181 : ctx.target->getImplicitAddend(
182 buf: sec->content().data() + r.r_offset, type);
183}
184
185template <class ELFT, class RelTy>
186void RelocScan::scan(typename Relocs<RelTy>::const_iterator &it, RelType type,
187 int64_t addend) {
188 const RelTy &rel = *it;
189 uint32_t symIdx = rel.getSymbol(false);
190 Symbol &sym = sec->getFile<ELFT>()->getSymbol(symIdx);
191 uint64_t offset = rel.r_offset;
192 RelExpr expr =
193 ctx.target->getRelExpr(type, s: sym, loc: sec->content().data() + offset);
194
195 // Ignore R_*_NONE and other marker relocations.
196 if (expr == R_NONE)
197 return;
198
199 // Error if the target symbol is undefined. Symbol index 0 may be used by
200 // marker relocations, e.g. R_*_NONE and R_ARM_V4BX. Don't error on them.
201 if (sym.isUndefined() && symIdx != 0 &&
202 maybeReportUndefined(sym&: cast<Undefined>(Val&: sym), offset))
203 return;
204
205 // Ensure GOT or GOTPLT is created for relocations that reference their base
206 // addresses without directly creating entries.
207 if (oneof<R_GOTPLTREL, R_GOTPLT, R_TLSGD_GOTPLT>(expr)) {
208 ctx.in.gotPlt->hasGotPltOffRel.store(i: true, m: std::memory_order_relaxed);
209 } else if (oneof<R_GOTONLY_PC, R_GOTREL, RE_PPC32_PLTREL>(expr)) {
210 ctx.in.got->hasGotOffRel.store(i: true, m: std::memory_order_relaxed);
211 }
212
213 // Process TLS relocations, including TLS optimizations. Note that
214 // R_TPREL and R_TPREL_NEG relocations are resolved in processAux.
215 //
216 // Some RISCV TLSDESC relocations reference a local NOTYPE symbol,
217 // but we need to process them in handleTlsRelocation.
218 if (sym.isTls() || oneof<R_TLSDESC_PC, R_TLSDESC_CALL>(expr)) {
219 if (unsigned processed =
220 handleTlsRelocation(expr, type, offset, sym, addend)) {
221 it += processed - 1;
222 return;
223 }
224 }
225
226 process(expr, type, offset, sym, addend);
227}
228
229// Dispatch to target-specific scanSectionImpl based on relocation format.
230template <class Target, class ELFT>
231void scanSection1(Target &target, InputSectionBase &sec) {
232 const RelsOrRelas<ELFT> rels = sec.template relsOrRelas<ELFT>();
233 if (rels.areRelocsCrel())
234 target.template scanSectionImpl<ELFT>(sec, rels.crels);
235 else if (rels.areRelocsRel())
236 target.template scanSectionImpl<ELFT>(sec, rels.rels);
237 else
238 target.template scanSectionImpl<ELFT>(sec, rels.relas);
239}
240
241} // namespace lld::elf
242
243#endif
244