On Fri, 18 Aug 2017, Maciej W. Rozycki wrote:

quoted

When building a kernel for the microMIPS ISA, ensure that the ISA bit
(ie. bit 0) in the entry address is set. Otherwise we may include an
entry address in images which bootloaders will jump to as MIPS32 code.

 Hmm, what's going on here?  The ISA bit is set by the linker according to 
the mode the code at the entry symbol has been assembled for, e.g.:

$ readelf -h vmlinux | grep Entry
  Entry point address:               0x804355e1
$ readelf -s vmlinux | grep kernel_entry
156535: 80100400     0 FUNC    GLOBAL DEFAULT [MICROMIPS]     1 __kernel_entry
156742: 804355e0   146 FUNC    GLOBAL DEFAULT [MICROMIPS]     1 kernel_entry
$ 

or no microMIPS (or MIPS16) executable could work.  Is your build process 
or toolchain used broken by any chance?

 It is indeed the build process.  You've come up with a valid, however a 
complicated solution.  How about the change below, on top of yours -- does 
it work for you?  If so, then I'll wrap it up and submit as an update.

  Maciej

---
 arch/mips/Makefile |   17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

linux-mips-start-address.diff
Index: linux-sfr-usead/arch/mips/Makefile
===================================================================

--- linux-sfr-usead.orig/arch/mips/Makefile	2017-08-18 15:25:58.196676000 +0100
+++ linux-sfr-usead/arch/mips/Makefile	2017-08-18 15:27:55.309653000 +0100

@@ -242,21 +242,8 @@ include arch/mips/Kbuild.platforms
 ifdef CONFIG_PHYSICAL_START
 load-y					= $(CONFIG_PHYSICAL_START)
 endif
-
-entry-noisa-y				= 0x$(shell $(NM) vmlinux 2>/dev/null \
-					| grep "\bkernel_entry\b" | cut -f1 -d \ )
-ifdef CONFIG_CPU_MICROMIPS
-  #
-  # Set the ISA bit, since the kernel_entry symbol in the ELF will have it
-  # clear which would lead to images containing addresses which bootloaders may
-  # jump to as MIPS32 code.
-  #
-  entry-y = $(patsubst %0,%1,$(patsubst %2,%3,$(patsubst %4,%5, \
-              $(patsubst %6,%7,$(patsubst %8,%9,$(patsubst %a,%b, \
-              $(patsubst %c,%d,$(patsubst %e,%f,$(entry-noisa-y)))))))))
-else
-  entry-y = $(entry-noisa-y)
-endif
+entry-y				= $(shell $(OBJDUMP) -f vmlinux 2>/dev/null \
+					| sed -n 's/start address //p')
 
 cflags-y			+= -I$(srctree)/arch/mips/include/asm/mach-generic
 drivers-$(CONFIG_PCI)		+= arch/mips/pci/