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MIPS: Set ISA bit in entry-y for microMIPS kernels

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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.

I originally tried using "objdump -f" to obtain the entry address, which
works for microMIPS but it always outputs a 32 bit address for a 32 bit
ELF whilst nm will sign extend to 64 bit. That matters for systems where
we might want to run a MIPS32 kernel on a MIPS64 CPU & load it with a
MIPS64 bootloader, which would then jump to a non-canonical
(non-sign-extended) address.

This works in all cases as it only changes the behaviour for microMIPS
kernels, but isn't the prettiest solution. A possible alternative would
be to write a custom tool to just extract, sign extend & print the entry
point of an ELF executable. I'm open to feedback if that would be
preferred.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16950/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton 2017-08-07 16:16:47 -07:00 committed by Ralf Baechle
parent 527f10285b
commit 5fc9484f5e
1 changed files with 14 additions and 1 deletions
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15
arch/mips/Makefile
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@ -243,8 +243,21 @@ include arch/mips/Kbuild.platforms
ifdef CONFIG_PHYSICAL_START
load-y = $(CONFIG_PHYSICAL_START)
endif
entry-y = 0x$(shell $(NM) vmlinux 2>/dev/null \
entry-noisa-y = 0x$(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 = $(entry-noisa-y)
endif
cflags-y += -I$(srctree)/arch/mips/include/asm/mach-generic
drivers-$(CONFIG_PCI) += arch/mips/pci/