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 syscalls 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.
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
---
arch/powerpc/include/asm/systbl.h | 1 +
arch/powerpc/include/asm/unistd.h | 2 +-
arch/powerpc/include/uapi/asm/unistd.h | 1 +
arch/powerpc/kernel/syscalls.c | 7 +++++++
4 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/systbl.h
b/arch/powerpc/include/asm/systbl.h
index 91062eef582f..524bf5dff9f9 100644
--- a/arch/powerpc/include/asm/systbl.h
+++ b/arch/powerpc/include/asm/systbl.h
@@ -367,3 +367,4 @@ SYSCALL_SPU(getrandom)
SYSCALL_SPU(memfd_create)
SYSCALL_SPU(bpf)
COMPAT_SYS(execveat)
+SYSCALL(switch_endian)
diff --git a/arch/powerpc/include/asm/unistd.h
b/arch/powerpc/include/asm/unistd.h
index 36b79c31eedd..f4f8b667d75b 100644
--- a/arch/powerpc/include/asm/unistd.h
+++ b/arch/powerpc/include/asm/unistd.h
@@ -12,7 +12,7 @@
#include <uapi/asm/unistd.h>
-#define __NR_syscalls 363
+#define __NR_syscalls 364
#define __NR__exit __NR_exit
#define NR_syscalls __NR_syscalls
diff --git a/arch/powerpc/include/uapi/asm/unistd.h
b/arch/powerpc/include/uapi/asm/unistd.h
index ef5b5b1f3123..e4aa173dae62 100644
--- a/arch/powerpc/include/uapi/asm/unistd.h
+++ b/arch/powerpc/include/uapi/asm/unistd.h
@@ -385,5 +385,6 @@
#define __NR_memfd_create 360
#define __NR_bpf 361
#define __NR_execveat 362
+#define __NR_switch_endian 363
#endif /* _UAPI_ASM_POWERPC_UNISTD_H_ */
diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c
index b2702e87db0d..0ea01957990e 100644
--- a/arch/powerpc/kernel/syscalls.c
+++ b/arch/powerpc/kernel/syscalls.c
@@ -121,3 +121,10 @@ 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)
+{
+ current->thread.regs->msr ^= MSR_LE;
+
+ return 0;
+}
--
2.1.0
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