1 //===- AVR.cpp ------------------------------------------------------------===//
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 // AVR is a Harvard-architecture 8-bit micrcontroller designed for small
10 // baremetal programs. All AVR-family processors have 32 8-bit registers.
11 // The tiniest AVR has 32 byte RAM and 1 KiB program memory, and the largest
12 // one supports up to 2^24 data address space and 2^22 code address space.
13 //
14 // Since it is a baremetal programming, there's usually no loader to load
15 // ELF files on AVRs. You are expected to link your program against address
16 // 0 and pull out a .text section from the result using objcopy, so that you
17 // can write the linked code to on-chip flush memory. You can do that with
18 // the following commands:
19 //
20 //   ld.lld -Ttext=0 -o foo foo.o
21 //   objcopy -O binary --only-section=.text foo output.bin
22 //
23 // Note that the current AVR support is very preliminary so you can't
24 // link any useful program yet, though.
25 //
26 //===----------------------------------------------------------------------===//
27 
28 #include "InputFiles.h"
29 #include "Symbols.h"
30 #include "Target.h"
31 #include "lld/Common/ErrorHandler.h"
32 #include "llvm/Object/ELF.h"
33 #include "llvm/Support/Endian.h"
34 
35 using namespace llvm;
36 using namespace llvm::object;
37 using namespace llvm::support::endian;
38 using namespace llvm::ELF;
39 
40 namespace lld {
41 namespace elf {
42 
43 namespace {
44 class AVR final : public TargetInfo {
45 public:
46   AVR();
47   RelExpr getRelExpr(RelType type, const Symbol &s,
48                      const uint8_t *loc) const override;
49   void relocateOne(uint8_t *loc, RelType type, uint64_t val) const override;
50 };
51 } // namespace
52 
53 AVR::AVR() { noneRel = R_AVR_NONE; }
54 
55 RelExpr AVR::getRelExpr(RelType type, const Symbol &s,
56                         const uint8_t *loc) const {
57   return R_ABS;
58 }
59 
60 void AVR::relocateOne(uint8_t *loc, RelType type, uint64_t val) const {
61   switch (type) {
62   case R_AVR_CALL: {
63     uint16_t hi = val >> 17;
64     uint16_t lo = val >> 1;
65     write16le(loc, read16le(loc) | ((hi >> 1) << 4) | (hi & 1));
66     write16le(loc + 2, lo);
67     break;
68   }
69   default:
70     error(getErrorLocation(loc) + "unrecognized relocation " + toString(type));
71   }
72 }
73 
74 TargetInfo *getAVRTargetInfo() {
75   static AVR target;
76   return &target;
77 }
78 
79 } // namespace elf
80 } // namespace lld
81