Info Catalog as: Xtensa Branch Relaxation as: Xtensa Relaxation as: Xtensa Jump Relaxation

as: Xtensa Call Relaxation

 
 9.54.4.2 Function Call Relaxation
 .................................
 
 Function calls may require relaxation because the Xtensa immediate call
 instructions ('CALL0', 'CALL4', 'CALL8' and 'CALL12') provide a
 PC-relative offset of only 512 Kbytes in either direction.  For larger
 programs, it may be necessary to use indirect calls ('CALLX0', 'CALLX4',
 'CALLX8' and 'CALLX12') where the target address is specified in a
 register.  The Xtensa assembler can automatically relax immediate call
 instructions into indirect call instructions.  This relaxation is done
 by loading the address of the called function into the callee's return
 address register and then using a 'CALLX' instruction.  So, for example:
 
          call8 func
 
    might be relaxed to:
 
          .literal .L1, func
          l32r    a8, .L1
          callx8  a8
 
    Because the addresses of targets of function calls are not generally
 known until link-time, the assembler must assume the worst and relax all
 the calls to functions in other source files, not just those that really
 will be out of range.  The linker can recognize calls that were
 unnecessarily relaxed, and it will remove the overhead introduced by the
 assembler for those cases where direct calls are sufficient.
 
    Call relaxation is disabled by default because it can have a negative
 effect on both code size and performance, although the linker can
 usually eliminate the unnecessary overhead.  If a program is too large
 and some of the calls are out of range, function call relaxation can be
 enabled using the '--longcalls' command-line option or the 'longcalls'
 directive (longcalls Longcalls Directive.).
 

Info Catalog as: Xtensa Branch Relaxation as: Xtensa Relaxation as: Xtensa Jump Relaxation