Subject: gcc options for amd64
To: None <>
From: David Laight <>
List: tech-toolchain
Date: 11/26/2005 20:20:39
I've just discovered that all our amd64 binaries have a large eh_frame
section.  This is data that is used by debuggers for processing exxeptions
(I'd guess C++).  There is no corresponding code....

If all comes about because of the following code in
src/gnu/dist/gcc/gcc/config/i386/i386.c near line 1019

  /* Set the default values for switches whose default depends on TARGET_64BIT
     in case they weren't overwriten by command line options.  */
  if (TARGET_64BIT)
      if (flag_omit_frame_pointer == 2)
        flag_omit_frame_pointer = 1;
      if (flag_asynchronous_unwind_tables == 2)
        flag_asynchronous_unwind_tables = 1;
      if (flag_pcc_struct_return == 2)
        flag_pcc_struct_return = 0;
      if (flag_omit_frame_pointer == 2)
        flag_omit_frame_pointer = 0;
      if (flag_asynchronous_unwind_tables == 2)
        flag_asynchronous_unwind_tables = 0;
      if (flag_pcc_struct_return == 2)
        flag_pcc_struct_return = DEFAULT_PCC_STRUCT_RETURN;

Which enables asynchronous_unwind_tables by default for amd64.
The general comments on these options seem to imply that they would
normally get set implicitly by -gxxxx (and similar) rather being
explicitly set on the command line.

In any case compiling the INSTALL kernel and ramdiskbin with
-fno-asynchronous-unwind-tables saves about 220kB after compression.


David Laight: