N2X, GR740 and coverage: The impact of a linkcmds patch from 2014 to gcov_init calls

Sebastian Huber sebastian.huber at embedded-brains.de
Wed Feb 28 11:12:57 UTC 2018

----- Am 27. Feb 2018 um 17:30 schrieb Thanassis Tsiodras Thanassis.Tsiodras at esa.int:

> After quite a lot of hunting, we traced this failure to a patch in the
> "linkcmds.base" - done back in 2014 ( commit 95cb09ed746 ) :
> This commit changed "c/src/lib/libbsp/sparc/shared/startup/linkcmds.base"
> from this:
>    KEEP (*(SORT(.ctors.*)))
>    KEEP (*(.ctors))
>    KEEP (*crtbegin.o(.dtors))
>    KEEP (*crtbegin?.o(.dtors))
>    KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
>    KEEP (*(SORT(.dtors.*)))
>    KEEP (*(.dtors))
> ...to this:
>    KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))
>    KEEP (*(SORT(.ctors*)))
>    KEEP (*crtbegin.o(.dtors))
>    KEEP (*crtbegin?.o(.dtors))
>    KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
>    KEEP (*(SORT(.dtors*)))
> Reverting this change, the gcov stubs revert back to their proper place,
> and __gcov_inits are called properly.
> The reason I tried this patch, was because I noticed that the coverage
> stubs are no longer placed in ".ctor" sections - they are instead placed
> by the newer compilers at ".ctor.NUMBER" sections (with NUMBER set to
> 65435 in my case - but I am guessing this will change from invocation to
> invocation).
> The comment provided by Joel back in 2014, only indicated that this patch
> was done to address C++ concerns:
> commit 95cb09ed746e7daeca2158c7ecdf0249cfcbc5c8
> Author: Joel Sherrill <joel.sherrill at oarcorp.com>
> Date:   Wed Apr 2 11:39:20 2014 -0500
>    sparc/shared/.../linkcmds.base: Correct C++ support
>    Add KEEP() for .eh_frame*, .ctor*, and .dtor*.

It could be a bug in the linker. The standard sections should be exactly like the Binutils default:

sparc-rtems5-ld --verbose | grep ctor -C 3
      *(.rela.data .rela.data.* .rela.gnu.linkonce.d.*)
      *(.rela.tdata .rela.tdata.* .rela.gnu.linkonce.td.*)
      *(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*)
      *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*)
  .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     :
    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          :

However, I am not able to reproduce this problem. For example in the sptls04 linker map file (-Wl,-Map,map.txt) we have this:

 .ctors         0x0000000002011330        0x4 /opt/rtems/5/lib/gcc/sparc-rtems5/7.3.0/crtbegin.o
 *(EXCLUDE_FILE(*crtend?.o *crtend.o) .ctors)
 .ctors         0x0000000002011334        0x4 init.o
 .ctors         0x0000000002011338        0x4 /opt/rtems/5/lib/gcc/sparc-rtems5/7.3.0/crtend.o

Who do the linker map files look in your test case?

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