Home | History | Annotate | Download | only in elfutils 
      1 Fundamental design decision:
      2 
      3 - the sizes of external and internal types are assumed to be the same.
      4   This leaves byte ordering aside.  While assuming this the code can be
      5   greatly simplified and speed increases.  Since no change violating this
      6   assumption is in sight this is believed to be a worthwhile optimization.
      7 
      8 - the ABI of the backend modules is not guaranteed.  Really, no guarantee
      9   whatsoever.  We are enforcing this in the code.  The modules and their
     10   users must match.  No third-party EBL module are supported or allowed.
     11   The only reason there are separate modules is to not have the code for
     12   all architectures in all the binaries.
     13 
     14 - although the public libraries (libasm, libdw) have a stable API and are
     15   backwards ABI compatible they, and the elfutils tools, do depend on each
     16   others internals, and on internals of libelf to provide their interfaces.
     17   So they should always be upgraded in lockstep when packaging the tools
     18   and libraries separately. For one example of how to do that, see the
     19   config/elfutils.spec.
     20 
     21 Some notes:
     22 
     23 - old GNU ld's behavior wrt DSOs seems to be severely broken.
     24 
     25      y.o reference foo()
     26      y1.o defines foo(), references bar()
     27      y2.o defines bar()
     28      libbar.so defines bar()
     29 
     30   Running
     31 
     32      gcc -o y y.o -lbar y1.o y2.o
     33 
     34   uses the bar() definition from libbar.so and does not mention the definition
     35   in y2.o at all (no duplicate symbol message).  Correct is to use the
     36   definition in y2.o.
     37 
     38 
     39      y.o reference foo()
     40      y1.o defines foo(), references bar()
     41      y2.o in liby2.a defines bar()
     42      libbar.so defines bar()
     43 
     44   Running
     45 
     46      gcc -o y y.o -lbar y1.o -ly3
     47 
     48   has to use the definition in -lbar and not pull the definition from liby3.a.
     49 
     50 
     51 - the old linker follows DT_NEEDED entries and adds the objects referenced
     52   this way which define a symbol which is needed as a DT_NEEDED to the
     53   generated binary.  This is wrong since the DT_NEEDED changes the search
     54   path in the object (which is breadth first).
     55 
     56 
     57 - the old linker supported extern "C++", extern "java" in version scripts.
     58   I believe this implementation is severly broken and needs a redesign
     59   (how do wildcards work with these languages*?).  Therefore it is left
     60   out for now.
     61 
     62 
     63 - what should happen if two sections in different files with the same
     64   name have different types and/or the flags are different
     65 
     66 
     67 - section names in input files are mostly irrelevant.  Exceptions:
     68 
     69   .comment/SHT_PROGBITS		in strip, ld
     70 
     71   .debug		\
     72   .line			|
     73   .debug_srcinfo	|
     74   .debug_sfnames	|
     75   .debug_aranges	|
     76   .debug_pubnames	|
     77   .debug_info		|
     78   .debug_abbrev		|
     79   .debug_line		|
     80   .debug_abbrev		 >	DWARF sections in ld
     81   .debug_line		|
     82   .debug_frame		|
     83   .debug_str		|
     84   .debug_loc		|
     85   .debug_macinfo	|
     86   .debug_weaknames	|
     87   .debug_funcnames	|
     88   .debug_typenames	|
     89   .debug_varnames	/
     90 
     91   Sections created in output files follow the naming of special section
     92   from the gABI.
     93 
     94   In no place is a section solely indentified by its name.  Internal
     95   references always use the section index.
     96