Re: MIPS: Handle manual calls of MIPS16 functions with a call stub

[Daniel Jacobowitz <drow at false dot org>]

On Thu, Jan 31, 2008 at 05:57:57PM +0000, Maciej W. Rozycki wrote:
> Hello,
> 
>  There is a problem with GDB calling some of MIPS16 functions manually.  
> It happens when such a function has a call stub (which is needed due to an 
> ABI difference when passing floating-point arguments when called from 
> standard MIPS code) and DWARF-2 information is available for the function.  
> In this case the stub, which is prepended to the function itself, is made 
> a part of the function's DWARF-2 subprogram block.  The PC range of the 
> block is determined by two labels that are put at the beginning and the 
> end of the block each.  GDB applies the least significant bit (LSB) of the 
> start address of a DWARF-2 block to its internal block structure 
> associated with a function and uses it to determine whether the function 
> is MIPS16 code (when set) or standard MIPS code (if clear).
> 
>  The bit in the start address is set in the DWARF-2 record by BFD at the 
> link time based on the STO_MIPS16 annotation of the symbol at the same 
> address in the ELF symbol table.  If the start address is the same as the 
> regular entry point of the function, which is the case when no call stub 
> has been generated for the function in question, then the DWARF-2 record 
> gets updated accordingly and the bit is correctly set.  However, when the 
> call stub indeed is there, the function's entry point is at a different 
> location, and the stub's entry point point is standard MIPS code and 
> therefore bearing no STO_MIPS16 annotation.  In this case the bit in the 
> DWARF-2 record remains clear.

Does this mean the DWARF block describes the MIPS16 parts, but the
function's minimal symbol points to the call stub, which is
elsewhere)?  Maybe mips_write_pc should use mips_pc_is_mips16; that's
how Thumb works, by always consulting the minimal symbol table to find
out whether an address should be called as MIPS16 or MIPS32.

-- 
Daniel Jacobowitz
CodeSourcery