[xen staging] x86/altcall: allow compound types to be passed

[patchbot@xxxxxxx]

commit 5c7c78d0be86e3ce0f96f0000f9462e1cafbdb6e
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Nov 4 17:04:05 2021 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Nov 29 13:53:05 2021 +0000

    x86/altcall: allow compound types to be passed
    
    Replace the conditional operator in ALT_CALL_ARG(), which was intended
    to limit usable types to scalar ones, by a size check. Some restriction
    here is necessary to make sure we don't violate the ABI's calling
    conventions, but limiting to scalar types was both too restrictive
    (disallowing e.g. guest handles) and too permissive (allowing e.g.
    __int128_t).
    
    Note that there was some anomaly with that conditional operator anyway:
    Something - I don't recall what - made it impossible to omit the middle
    operand.
    
    Code-generation-wise this has the effect of removing certain zero- or
    sign-extending in some altcall invocations. This ought to be fine as the
    ABI doesn't require sub-sizeof(int) values to be extended, except when
    passed through an ellipsis. No functions subject to altcall patching has
    a variable number of arguments, though.
    
    Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    
    Unfortunately this triggers -Werror=sizeof-array-argument on some versions 
of
    GCC, so alter xsm_{alloc,free}_security_evtchns() to use a pointer rather 
than
    array parameter.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
---
 xen/include/asm-x86/alternative.h | 4 ++--
 xen/include/xsm/xsm.h             | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/include/asm-x86/alternative.h 
b/xen/include/asm-x86/alternative.h
index 8e78cc91c3..8bc59b02af 100644
--- a/xen/include/asm-x86/alternative.h
+++ b/xen/include/asm-x86/alternative.h
@@ -168,8 +168,8 @@ extern void alternative_branches(void);
 #define ALT_CALL_arg6 "r9"
 
 #define ALT_CALL_ARG(arg, n) \
-    register typeof((arg) ? (arg) : 0) a ## n ## _ \
-    asm ( ALT_CALL_arg ## n ) = (arg)
+    register typeof(arg) a ## n ## _ asm ( ALT_CALL_arg ## n ) = \
+        ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); })
 #define ALT_CALL_NO_ARG(n) \
     register unsigned long a ## n ## _ asm ( ALT_CALL_arg ## n )
 
diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
index c101e653f6..0b360e1a35 100644
--- a/xen/include/xsm/xsm.h
+++ b/xen/include/xsm/xsm.h
@@ -332,13 +332,13 @@ static inline void xsm_free_security_domain(struct domain 
*d)
 }
 
 static inline int xsm_alloc_security_evtchns(
-    struct evtchn chn[], unsigned int nr)
+    struct evtchn *chn, unsigned int nr)
 {
     return alternative_call(xsm_ops.alloc_security_evtchns, chn, nr);
 }
 
 static inline void xsm_free_security_evtchns(
-    struct evtchn chn[], unsigned int nr)
+    struct evtchn *chn, unsigned int nr)
 {
     alternative_vcall(xsm_ops.free_security_evtchns, chn, nr);
 }
--
generated by git-patchbot for /home/xen/git/xen.git#staging