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: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/b8192e8a-13ef-6ac6-6364-8ba58992cd1d@suse.com

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index a69012e..e159146 100644 (file)
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -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