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author | Michael Ellerman <mpe@ellerman.id.au> | 2015-03-28 11:35:16 +0100 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2015-03-28 12:03:40 +0100 |
commit | 529d235a0e190ded1d21ccc80a73e625ebcad09b (patch) | |
tree | c807f7526f29b79a7ce0b233daf8a1c3030d8dd0 /arch/powerpc/kernel/syscalls.c | |
parent | powerpc/pseries: Simplify check for suspendability during suspend/migration (diff) | |
download | linux-529d235a0e190ded1d21ccc80a73e625ebcad09b.tar.xz linux-529d235a0e190ded1d21ccc80a73e625ebcad09b.zip |
powerpc: Add a proper syscall for switching endianness
We currently have a "special" syscall for switching endianness. This is
syscall number 0x1ebe, which is handled explicitly in the 64-bit syscall
exception entry.
That has a few problems, firstly the syscall number is outside of the
usual range, which confuses various tools. For example strace doesn't
recognise the syscall at all.
Secondly it's handled explicitly as a special case in the syscall
exception entry, which is complicated enough without it.
As a first step toward removing the special syscall, we need to add a
regular syscall that implements the same functionality.
The logic is simple, it simply toggles the MSR_LE bit in the userspace
MSR. This is the same as the special syscall, with the caveat that the
special syscall clobbers fewer registers.
This version clobbers r9-r12, XER, CTR, and CR0-1,5-7.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/syscalls.c')
-rw-r--r-- | arch/powerpc/kernel/syscalls.c | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c index b2702e87db0d..5fa92706444b 100644 --- a/arch/powerpc/kernel/syscalls.c +++ b/arch/powerpc/kernel/syscalls.c @@ -121,3 +121,20 @@ long ppc_fadvise64_64(int fd, int advice, u32 offset_high, u32 offset_low, return sys_fadvise64(fd, (u64)offset_high << 32 | offset_low, (u64)len_high << 32 | len_low, advice); } + +long sys_switch_endian(void) +{ + struct thread_info *ti; + + current->thread.regs->msr ^= MSR_LE; + + /* + * Set TIF_RESTOREALL so that r3 isn't clobbered on return to + * userspace. That also has the effect of restoring the non-volatile + * GPRs, so we saved them on the way in here. + */ + ti = current_thread_info(); + ti->flags |= _TIF_RESTOREALL; + + return 0; +} |