.init_array vs. .ctors sections on ARM

Sebastian Huber sebastian.huber@embedded-brains.de
Tue Oct 9 07:41:00 GMT 2018


Hello,

the default linker command file on ARM ELF looks like this 
(arm-none-eabi-ld --verbose):

...
   .init_array     :
   {
     PROVIDE_HIDDEN (__init_array_start = .);
     KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) 
SORT_BY_INIT_PRIORITY(.ctors.*)))
     KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o 
*crtend.o *crtend?.o ) .ctors))
     PROVIDE_HIDDEN (__init_array_end = .);
   }
   .fini_array     :
   {
     PROVIDE_HIDDEN (__fini_array_start = .);
     KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) 
SORT_BY_INIT_PRIORITY(.dtors.*)))
     KEEP (*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o 
*crtend.o *crtend?.o ) .dtors))
     PROVIDE_HIDDEN (__fini_array_end = .);
   }
   .ctors          :
   {
     /* gcc uses crtbegin.o to find the start of
        the constructors, so we make sure it is
        first.  Because this is a wildcard, it
        doesn't matter if the user does not
        actually link against crtbegin.o; the
        linker won't look for a file to match a
        wildcard.  The wildcard also means that it
        doesn't matter which directory crtbegin.o
        is in.  */
     KEEP (*crtbegin.o(.ctors))
     KEEP (*crtbegin?.o(.ctors))
     /* We don't want to include the .ctor section from
        the crtend.o file until after the sorted ctors.
        The .ctor section from the crtend file contains the
        end of ctors marker and it must be last */
     KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))
     KEEP (*(SORT(.ctors.*)))
     KEEP (*(.ctors))
   }
   .dtors          :
   {
     KEEP (*crtbegin.o(.dtors))
     KEEP (*crtbegin?.o(.dtors))
     KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
     KEEP (*(SORT(.dtors.*)))
     KEEP (*(.dtors))
   }
...

Why are the .ctors and .dtors input sections used in two output 
sections? Would this result in two output sections with partly identical 
content?

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
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