19. Target Specific Features

19.1. Hexagon

  • Plugins - Information can be found at Linker Plugins

  • Small data

  • Trampolines

  • –disable-guard-for-weak-undef - Disable guard for weak undefined symbols

  • -gpsize=<value> - Set the maximum size of objects to be optimized using GP

19.2. ARM

  • Baremetal

  • Thumb

  • ARM

  • Linux

  • Android

  • Supported errata fixes - fix_cortex_a8 - fix_cortex_a53_843419

  • enable-bss-mixing - Enable mixing of BSS and non-BSS sections

  • -execute-only - Mark executable sections execute-only

  • –disable-bss-conversion - Don’t convert BSS to NonBSS when BSS/NonBSS sections are mixed

  • –use-mov-veneer - Use movt/movw to load address in veneers with absolute relocation

  • –compact

    • --compact is used to reduce the output ELF size.

    • The loader must be able to load such ELF files and satisfy segmentaddr - sectionaddr == segmentoffset - sectionoffset.

    • Offsets are incremented by section size, not by virtual address difference.

    • Supported only in ARM/AArch64 baremetal environments (typically low memory).

    Note

    The impact of --compact can be observed by checking the segment sizes.

    Note

    • File offset of every section must be consistent with physical address of the segment:

      Section_file_offset - segment_file_offset
  == section_physical_address - segment_physical_address

    • If a section does not respect the rule, the linker reports an error.

    • The image must still be a valid ELF; in particular:

      offset % page_alignment
  == physical_address % page_alignment
  == virtual_address % page_alignment

    Example showing --compact reducing segment size to 0x20 as seen from readelf -l:

    $ cat script.t
PHDRS {
  A PT_LOAD;
}

SECTIONS {
  .A (0x1000) : AT(0x1000) { *(.text.foo) *(.ARM.exidx.text.foo) } :A
  .B (0x10000) : { *(.text.bar) *(.ARM.exidx.text.bar) } :A
}

$ arm-link 1.o -T script.t -o t4.out --compact
$ llvm-readelf -S -W t4.out
  There are 8 section headers, starting at offset 0x220:

  Section Headers:
  [Nr] Name Type Address Off Size ES Flg Lk Inf Al
  [ 0] NULL      00000000 000000 000000 00 0  0  0
  [ 1] .A PROGBITS 00001000 000054 000010 00 AX 0  0  4
  [ 2] .B PROGBITS 00010000 000064 000010 00 AX 0  0  4

$ llvm-readelf -l -W t4.out
  Elf file type is EXEC (Executable file)
  Entry point 0x0
  There are 1 program headers, starting at offset 52

  Program Headers:
    Type Offset   VirtAddr   PhysAddr   FileSiz MemSiz Flg Align
    LOAD 0x000054 0x00001000 0x00001000 0x00020 0x0f010 R E 0x4

  Section to Segment mapping:
    Segment Sections...
    00      .A .B
    None    .ARM.attributes .comment .shstrtab .symtab .strtab

19.3. AArch64

  • Baremetal

  • AArch64

  • Linux

  • Android

  • enable-bss-mixing - Enable mixing of BSS and non-BSS sections

  • –disable-bss-conversion - Don’t convert BSS to NonBSS when BSS/NonBSS sections are mixed

  • –use-mov-veneer - Use movt/movw to load address in veneers with absolute relocation

  • –compact

  • -z nognustack - Do not create a GNU_STACK segment

19.4. RISCV

  • Baremetal

  • Linux

  • -gpsize=<value> - Set the maximum size of objects to be optimized using GP

  • Supports relaxation - --relax (enabled by default) - -no-relax to disable relaxation

  • enable-bss-mixing - Enable mixing of BSS and non-BSS sections

  • -W[no]attribute-mix - Warn about RISC-V attributes mix instead of failing to link

  • –disable-bss-conversion - Don’t convert BSS to NonBSS when BSS/NonBSS sections are mixed