Rather than trying to reconstruct the ISA bit by hand use the ELF entry
point recorded in the kernel executable itself, by parsing the output of
`objdump -f' and sign-extending the address retrieved if 32-bit. The
tool always prints the entry point using either 8 or 16 hexadecimal
digits even in the presence of leading zeros, matching the address width
(class) of the ELF file.
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxx>
---
On Sat, 19 Aug 2017, James Hogan wrote:
> >+# Knowing that a 32-bit kernel will be linked at a KSEG address
>
> thats not true with CONFIG_KVM_GUEST kernels, which use a separate set
> of emulated guest kernel segments in useg, i.e. at 0x40000000. I've also
> seen EVA kernels linked at low addresses like around 0x20000000, though
> entry gets a bit fiddly for EVA depending on whether bootloader already
> has the chosen segment configuration set up.
I wasn't aware of that. So we need a slightly more robust `sed' program,
like the below. It handles any 32-bit address now. I hope the formatting
is fine.
Please apply.
Maciej
---
arch/mips/Makefile | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)
linux-mips-start-address.diff
Index: linux-sfr-usead/arch/mips/Makefile
===================================================================
--- linux-sfr-usead.orig/arch/mips/Makefile 2017-08-18 22:17:42.962681000 +0100
+++ linux-sfr-usead/arch/mips/Makefile 2017-08-21 17:47:16.802753000 +0100
@@ -244,20 +244,11 @@ 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
+# Sign-extend the entry point to 64 bits if retrieved as a 32-bit number.
+entry-y = $(shell $(OBJDUMP) -f vmlinux 2>/dev/null \
+ | sed -n '/^start address / { \
+ s/^.*0x\([0-7].......\)$$/0x00000000\1/; \
+ s/^.*0x\(........\)$$/0xffffffff\1/; p }')
cflags-y += -I$(srctree)/arch/mips/include/asm/mach-generic
drivers-$(CONFIG_PCI) += arch/mips/pci/
