Enable OpenSBI to support position independent execution. Because the
position independent code will cause an additional GOT reference when
accessing the global variables, it will reduce performance a bit. Therefore,
the position independent execution is disabled by default. Users can
through specifying "FW_PIC=y" on the make command to enable this feature.
In theory, after enabling position-independent execution, the OpenSBI
can run at arbitrary address with appropriate alignment. Therefore, the
original relocation mechanism will be skipped. In other words, OpenSBI will
directly run at the load address without any code movement.
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
When OpenSBI is compiled as fPIE mode, the assembler will translate "la"
to GOT reference pattern. It will cause to cost an additional load
instruction when obtaining the symbol address. However, if the symbol
locates within the positive or negative 2GB region, we can use "lla"
instead of "la" to avoid unneeded GOT references. This patch assumes that
the OpenSBI image excluding the payload does not exceed 2GB. Based on
this assumption, all "la" instructions are replaced by "lla" to avoid
performance degradation when compiling as fPIE mode.
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
