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64-bit PowerPC and small data area?


Hello,

in the PowerPC ELFv2 specification

https://members.openpowerfoundation.org/document/dl/576

we have

"3.4.2 Use of the Small Data Area

For a data item in the .sdata or .sbss sections, a compiler may generate short-form one-instruction refer- ences. In an executable file or shared library, such a reference is relative to the address of the TOC base symbol (which can be obtained from r2 if a TOC pointer is initialized). A compiler that generates code using the small data area should provide an option to select the maximum size of objects placed in the small data area, and a means of disabling any use of the small data area. When generating code for ELF shared libraries, the small data area should not be used for default-visibility global objects. This is to satisfy ELF shared-library symbol interposition rules. That is, an ordinary global symbol in a shared library may be over- ridden by a symbol of the same name defined in the executable or another shared library. Supporting interpo- sition when using TOC-pointer relative addressing would require text relocations."

I tried to generate code using the small data area on a 64-bit PowerPC GCC, but I was not successful. We have in the GCC sources (gcc/config/rs6000/rs6000.c):

/* Return 1 for an operand in small memory on V.4/eabi.  */

int
small_data_operand (rtx op ATTRIBUTE_UNUSED,
            machine_mode mode ATTRIBUTE_UNUSED)
{
#if TARGET_ELF
  rtx sym_ref;

  if (rs6000_sdata == SDATA_NONE || rs6000_sdata == SDATA_DATA)
    return 0;

  if (DEFAULT_ABI != ABI_V4)
    return 0;

So, it looks like the small data stuff is not support for ABI_ELFv2? Are there main issues with the small data area using ELVv2 or is this simply not implemented due to a lack of interested?


--
Sebastian Huber, embedded brains GmbH

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