Commit 727f1361 authored Oct 09, 2017 by Michael Ellerman

powerpc: Disable the fast-endian switch syscall by default



Back in 2008 we added support for "fast little-endian switch" in the
syscall path. This added a special case syscall number 0x1ebe, which
is caught very early in the system call exception and switches endian
with as little overhead as possible. See commit 745a14cc
("[POWERPC] Add fast little-endian switch system call") for full
details.

Although it is fast, it's also completely non standard. The "syscall
number" is out of the range of normal syscalls, it can't be traced or
audited, and it's a bit of a wart. To the best of our knowledge it was
only used by one program, now long since discontinued.

So in an effort to shake out any current users, put it behind a config
option, and make it default n. If anyone *is* using it they can
quickly reinstate it with a rebuild, and we can flip it to default y.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent 5c2511bf

arch/powerpc/Kconfig.debug

+6 −0

Original line number	Diff line number	Diff line
		@@ -369,4 +369,10 @@ config PPC_HTDUMP
		def_bool y
		depends on PPC_PTDUMP && PPC_BOOK3S

		config PPC_FAST_ENDIAN_SWITCH
		bool "Deprecated fast endian-switch syscall"
		depends on DEBUG_KERNEL && PPC_BOOK3S_64
		help
		If you're unsure what this is, say N.

		endmenu

arch/powerpc/kernel/exceptions-64s.S

+5 −0

Original line number	Diff line number	Diff line
		@@ -879,6 +879,7 @@ EXC_COMMON(trap_0b_common, 0xb00, unknown_exception)
		rfid ; \
		b . ; /* prevent speculative execution */

		#ifdef CONFIG_PPC_FAST_ENDIAN_SWITCH
		#define SYSCALL_FASTENDIAN_TEST \
		BEGIN_FTR_SECTION \
		cmpdi r0,0x1ebe ; \
		@@ -893,6 +894,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) \
		mr r13,r9 ; \
		rfid ; /* return to userspace */ \
		b . ; /* prevent speculative execution */
		#else
		#define SYSCALL_FASTENDIAN_TEST
		#define SYSCALL_FASTENDIAN
		#endif /* CONFIG_PPC_FAST_ENDIAN_SWITCH */

		#if defined(CONFIG_RELOCATABLE)
		/*