Commit 2e1f8e55 authored by Jan Beulich's avatar Jan Beulich Committed by Borislav Petkov
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x86/paravirt: Use %rip-relative addressing in hook calls 



While using a plain (constant) address works, its use needlessly invokes
a SIB addressing mode, making every call site one byte larger than
necessary:

  ff 14 25 98 89 42 82    call   *0xffffffff82428998

Instead of using an "i" constraint with address-of operator and a 'c'
operand modifier, simply use an ordinary "m" constraint, which the
64-bit compiler will translate to %rip-relative addressing:

  ff 15 62 fb d2 00       call   *0xd2fb62(%rip)	# ffffffff82428998 <pv_ops+0x18>

This way the compiler is also told the truth about operand usage - the
memory location gets actually read, after all.

32-bit code generation is unaffected by the change.

  [ bp: Remove "we", add examples. ]

Signed-off-by: default avatarJan Beulich <jbeulich@suse.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/b8192e8a-13ef-6ac6-6364-8ba58992cd1d@suse.com
parent e783362e

arch/x86/include/asm/paravirt_types.h

+2 −2
Original line number Diff line number Diff line
@@ -279,7 +279,7 @@ extern void (*paravirt_iret)(void); 


#define paravirt_type(op)				\

	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\

	[paravirt_opptr] "i" (&(pv_ops.op))

	[paravirt_opptr] "m" (pv_ops.op)

#define paravirt_clobber(clobber)		\

	[paravirt_clobber] "i" (clobber)
@@ -316,7 +316,7 @@ int paravirt_disable_iospace(void); 
 */

#define PARAVIRT_CALL					\

	ANNOTATE_RETPOLINE_SAFE				\

	"call *%c[paravirt_opptr];"

	"call *%[paravirt_opptr];"



/*

 * These macros are intended to wrap calls through one of the paravirt