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Commit 9a036b93 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/signal/64: Remove 'fs' and 'gs' from sigcontext 



As far as I can tell, these fields have been set to zero on save
and ignored on restore since Linux was imported into git.
Rename them '__pad1' and '__pad2' to avoid confusion.  This may
also allow us to recycle them some day.

This also adds a comment clarifying the history of those fields.

I'm intentionally avoiding calling either of them '__pad0': the
field formerly known as '__pad0' is now 'ss'.

Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/844f8490e938780c03355be4c9b69eb4c494bf4e.1426193719.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c6f20629

arch/x86/include/asm/sigcontext.h

+2 −2
Original line number Diff line number Diff line
@@ -57,8 +57,8 @@ struct sigcontext { 
	unsigned long ip;

	unsigned long flags;

	unsigned short cs;

	unsigned short gs;

	unsigned short fs;

	unsigned short __pad2;	/* Was called gs, but was always zero. */

	unsigned short __pad1;	/* Was called fs, but was always zero. */

	unsigned short ss;

	unsigned long err;

	unsigned long trapno;

arch/x86/include/uapi/asm/sigcontext.h

+17 −2
Original line number Diff line number Diff line
@@ -177,8 +177,23 @@ struct sigcontext { 
	__u64 rip;

	__u64 eflags;		/* RFLAGS */

	__u16 cs;

	__u16 gs;

	__u16 fs;



	/*

	 * Prior to 2.5.64 ("[PATCH] x86-64 updates for 2.5.64-bk3"),

	 * Linux saved and restored fs and gs in these slots.  This

	 * was counterproductive, as fsbase and gsbase were never

	 * saved, so arch_prctl was presumably unreliable.

	 *

	 * If these slots are ever needed for any other purpose, there

	 * is some risk that very old 64-bit binaries could get

	 * confused.  I doubt that many such binaries still work,

	 * though, since the same patch in 2.5.64 also removed the

	 * 64-bit set_thread_area syscall, so it appears that there is

	 * no TLS API that works in both pre- and post-2.5.64 kernels.

	 */

	__u16 __pad2;		/* Was gs. */

	__u16 __pad1;		/* Was fs. */



	__u16 ss;

	__u64 err;

	__u64 trapno;

arch/x86/kernel/signal.c

+2 −2
Original line number Diff line number Diff line
@@ -155,8 +155,8 @@ int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate, 
#else /* !CONFIG_X86_32 */

		put_user_ex(regs->flags, &sc->flags);

		put_user_ex(regs->cs, &sc->cs);

		put_user_ex(0, &sc->gs);

		put_user_ex(0, &sc->fs);

		put_user_ex(0, &sc->__pad2);

		put_user_ex(0, &sc->__pad1);

		put_user_ex(regs->ss, &sc->ss);

#endif /* CONFIG_X86_32 */