[PATCH] D37615: [AVR] implement the relocation of LDI and other Instructions for LLD

[Leslie Zhai via Phabricator via llvm-commits]

xiangzhai updated this revision to Diff 114546.
xiangzhai retitled this revision from "[AVR] implement the relocation of LDI for LLD" to "[AVR] implement the relocation of LDI and other Instructions for LLD".
xiangzhai added a comment.

Dear Rui,

> I believe you want to learn/investigate more about ELF/AVR to write code for an ELF/AVR linker.

Yes 先生 :) and I read ld.bfd's elf32-avr.c <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf32-avr.c;h=830da288f3cd3e6a070b5ced908ca05d6b11e4b0;hb=HEAD#l1013> `avr_final_link_relocate`, then re-implement the relocation of LDI and other Instructions for LLD, tested by `make check-lld` and compared with avr-ld, the result is same:

  $ avr-gcc -mmcu=atmega328p -o basic-avr.o -c basic-avr.s
  $ avr-readelf -r basic-avr.o 
  
  Relocation section '.rela.text' at offset 0xe4 contains 10 entries:
   Offset     Info    Type            Sym.Value  Sym. Name + Addend
  00000000  00000106 R_AVR_LO8_LDI     00000000   .text + 12
  00000002  00000107 R_AVR_HI8_LDI     00000000   .text + 16
  00000004  00000108 R_AVR_HH8_LDI     00000000   .text + 12
  00000006  00000113 R_AVR_LDI         00000000   .text + 12
  00000008  00000102 R_AVR_7_PCREL     00000000   .text + e
  0000000a  00000103 R_AVR_13_PCREL    00000000   .text + e
  0000000c  00000115 R_AVR_6_ADIW      00000000   .text + 16
  0000000e  00000112 R_AVR_CALL        00000000   .text + e
  00000012  00000112 R_AVR_CALL        00000000   .text + 12
  00000016  00000112 R_AVR_CALL        00000000   .text + 16

relocated by avr-ld:

  $ avr-ld -o basic-avr basic-avr.o -Ttext=0
  $ avr-objdump -d basic-avr
  
  basic-avr:     file format elf32-avr
  
  
  Disassembly of section .text:
  
  00000000 <__ctors_end>:
     0:   12 e1           ldi     r17, 0x12       ; 18
     2:   20 e0           ldi     r18, 0x00       ; 0
     4:   30 e0           ldi     r19, 0x00       ; 0
     6:   42 e1           ldi     r20, 0x12       ; 18
     8:   11 f4           brne    .+4             ; 0xe <next>
     a:   01 c0           rjmp    .+2             ; 0xe <next>
     c:   46 96           adiw    r24, 0x16       ; 22
  
  0000000e <next>:
     e:   0c 94 07 00     jmp     0xe     ; 0xe <next>
  
  00000012 <foo>:
    12:   0c 94 09 00     jmp     0x12    ; 0x12 <foo>
  
  00000016 <bar>:
    16:   0c 94 0b 00     jmp     0x16    ; 0x16 <bar>

compared with LLD, the result is same:

  $ llvm/build/bin/ld.lld -o basic-avr-lld basic-avr.o -Ttext=0
  $ avr-objdump -d basic-avr-lld
  
  basic-avr-lld:     file format elf32-avr
  
  
  Disassembly of section .text:
  
  00000000 <main>:
     0:   12 e1           ldi     r17, 0x12       ; 18
     2:   20 e0           ldi     r18, 0x00       ; 0
     4:   30 e0           ldi     r19, 0x00       ; 0
     6:   42 e1           ldi     r20, 0x12       ; 18
     8:   11 f4           brne    .+4             ; 0xe <next>
     a:   01 c0           rjmp    .+2             ; 0xe <next>
     c:   46 96           adiw    r24, 0x16       ; 22
  
  0000000e <next>:
     e:   0c 94 07 00     jmp     0xe     ; 0xe <next>
  
  00000012 <foo>:
    12:   0c 94 09 00     jmp     0x12    ; 0x12 <foo>
  
  00000016 <bar>:
    16:   0c 94 0b 00     jmp     0x16    ; 0x16 <bar>

先生 please review my patch, thanks a lot!

Regards,
Leslie Zhai


Repository:
  rL LLVM

https://reviews.llvm.org/D37615

Files:
  ELF/Arch/AVR.cpp
  test/ELF/basic-avr.s

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