Why do STM32 gcc linker scripts automatically discard all input sections from these standard libraries: libc.a, libm.a, libgcc.a?

Question

From the bottom of any auto-generated STM32CubeMx-generated linker script:

/* Remove information from the standard libraries */
/DISCARD/ :
{
  libc.a ( * )
  libm.a ( * )
  libgcc.a ( * )
}

From the GNU Binutils ld (linker script) manual, 3.6.7 Output Section Discarding:

The special output section name ‘/DISCARD/’ may be used to discard input sections. Any input sections which are assigned to an output section named ‘/DISCARD/’ are not included in the output file.

What do these 3 input object files contain, and why do we discard everything (all input sections) from them?

Other STM32 linker script topics of interest:

I think to get an answer for this, someone needs to go ask ST the company and/or ARM the company directly, and report back. — Gabriel Staples, Jan 28 '21 at 03:47

score 3 · Answer 1 · answered May 13 '20 at 19:17

Looks like in this example, /DISCARD/ removes any other sections, that are not explicitly defined by script. For example, since *(.text), *(.data), *(.bss), *(.init_array) etc, has been defined earlier in the script, they get into the ELF. But libc, libm or libgcc could contain unnecessary sections for firmware (e.g. .foo, .bar, .debug ...), so /DISCARD/ just wipes them out, but NOT all sections!

Why do STM32 gcc linker scripts automatically discard all input sections from these standard libraries: libc.a, libm.a, libgcc.a?

Other STM32 linker script topics of interest:

1 Answers1

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