srxfixup: handle R_MIPS_NONE relocation; use --relative-branch in IOP builds

R_MIPS_NONE is a valid no-op relocation type that newer toolchains emit
(e.g. as padding between real relocations). srxfixup's fixlocation_an_rel()
had no case for it and would fall through to the default unhandled-relocation
path, causing srxfixup to abort when building any IRX that contained one.

Enable --relative-branch (--rb) in iop/Rules.make so that all IOP IRX
binaries have their R_MIPS_26 absolute-jump relocations converted to
position-independent relative branches. Without this, a module loaded at a
different address than it was linked for will execute the wrong jal target.

Author: fjtrujy

iop/Rules.make

@@ -146,7 +146,7 @@ $(IOP_BIN_STRIPPED_ELF): $(IOP_BIN_ELF)
 	$(IOP_STRIP) --strip-unneeded --remove-section=.pdr --remove-section=.comment --remove-section=.mdebug.abi32 --remove-section=.gnu.attributes -o $@ $<
 
 $(IOP_BIN): $(IOP_BIN_STRIPPED_ELF) $(PS2SDKSRC)/tools/srxfixup/bin/srxfixup
-	$(PS2SDKSRC)/tools/srxfixup/bin/srxfixup --irx1 -o $@ $<
+	$(PS2SDKSRC)/tools/srxfixup/bin/srxfixup --rb --irx1 -o $@ $<
 
 $(IOP_LIB)_tmp$(MAKE_CURPID): $(IOP_OBJS)
 	$(DIR_GUARD)

tools/srxfixup/src/srxgen.c

@@ -412,6 +412,8 @@ static void fixlocation_an_rel(elf_section *relsect, unsigned int startaddr)
 		datal = &relsect->info->data[rp->rel.r_offset - relsect->info->shr.sh_addr];
 		switch ( rp->type )
 		{
+			case R_MIPS_NONE:
+				break;
 			case R_MIPS_16:
 				data_1 = startaddr + (int16_t)*(uint32_t *)datal;
 				if ( (uint16_t)(data_1 >> 16) )