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commit 2f49d9f89c14519d4cb1e06ab8370cf4ba50fab7
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Tue Mar 5 12:00:47 2024 +0100
Commit: Jan Beulich <jbeulich@suse.com>
CommitDate: Tue Mar 5 12:00:47 2024 +0100

x86/altcall: always use a temporary parameter stashing variable

The usage in ALT_CALL_ARG() on clang of:

register union {
typeof(arg) e;
const unsigned long r;
} ...

When `arg` is the first argument to alternative_{,v}call() and
const_vlapic_vcpu() is used results in clang 3.5.0 complaining with:

arch/x86/hvm/vlapic.c:141:47: error: non-const static data member must be initialized out of line
alternative_call(hvm_funcs.test_pir, const_vlapic_vcpu(vlapic), vec) )

Workaround this by pulling `arg1` into a local variable, like it's done for
further arguments (arg2, arg3...)

Originally arg1 wasn't pulled into a variable because for the a1_ register
local variable the possible clobbering as a result of operators on other
variables don't matter:

https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html#Local-Register-Variables

Note clang version 3.8.1 seems to already be fixed and don't require the
workaround, but since it's harmless do it uniformly everywhere.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Fixes: 2ce562b2a413 ('x86/altcall: use a union as register type for function parameters on clang')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: c20850540ad6a32f4fc17bde9b01c92b0df18bf0
master date: 2024-02-29 08:21:49 +0100
---
xen/arch/x86/include/asm/alternative.h | 36 ++++++++++++++++++++++------------
1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/include/asm/alternative.h b/xen/arch/x86/include/asm/alternative.h
index bcb1dc94f4..fa04481316 100644
--- a/xen/arch/x86/include/asm/alternative.h
+++ b/xen/arch/x86/include/asm/alternative.h
@@ -253,21 +253,24 @@ extern void alternative_branches(void);
})

#define alternative_vcall1(func, arg) ({ \
- ALT_CALL_ARG(arg, 1); \
+ typeof(arg) v1_ = (arg); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_NO_ARG2; \
(void)sizeof(func(arg)); \
(void)alternative_callN(1, int, func); \
})

#define alternative_call1(func, arg) ({ \
- ALT_CALL_ARG(arg, 1); \
+ typeof(arg) v1_ = (arg); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_NO_ARG2; \
alternative_callN(1, typeof(func(arg)), func); \
})

#define alternative_vcall2(func, arg1, arg2) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_NO_ARG3; \
(void)sizeof(func(arg1, arg2)); \
@@ -275,17 +278,19 @@ extern void alternative_branches(void);
})

#define alternative_call2(func, arg1, arg2) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_NO_ARG3; \
alternative_callN(2, typeof(func(arg1, arg2)), func); \
})

#define alternative_vcall3(func, arg1, arg2, arg3) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_NO_ARG4; \
@@ -294,9 +299,10 @@ extern void alternative_branches(void);
})

#define alternative_call3(func, arg1, arg2, arg3) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_NO_ARG4; \
@@ -305,10 +311,11 @@ extern void alternative_branches(void);
})

#define alternative_vcall4(func, arg1, arg2, arg3, arg4) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
typeof(arg4) v4_ = (arg4); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_ARG(v4_, 4); \
@@ -318,10 +325,11 @@ extern void alternative_branches(void);
})

#define alternative_call4(func, arg1, arg2, arg3, arg4) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
typeof(arg4) v4_ = (arg4); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_ARG(v4_, 4); \
@@ -332,11 +340,12 @@ extern void alternative_branches(void);
})

#define alternative_vcall5(func, arg1, arg2, arg3, arg4, arg5) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
typeof(arg4) v4_ = (arg4); \
typeof(arg5) v5_ = (arg5); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_ARG(v4_, 4); \
@@ -347,11 +356,12 @@ extern void alternative_branches(void);
})

#define alternative_call5(func, arg1, arg2, arg3, arg4, arg5) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
typeof(arg4) v4_ = (arg4); \
typeof(arg5) v5_ = (arg5); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_ARG(v4_, 4); \
@@ -363,12 +373,13 @@ extern void alternative_branches(void);
})

#define alternative_vcall6(func, arg1, arg2, arg3, arg4, arg5, arg6) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
typeof(arg4) v4_ = (arg4); \
typeof(arg5) v5_ = (arg5); \
typeof(arg6) v6_ = (arg6); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_ARG(v4_, 4); \
@@ -379,12 +390,13 @@ extern void alternative_branches(void);
})

#define alternative_call6(func, arg1, arg2, arg3, arg4, arg5, arg6) ({ \
+ typeof(arg1) v1_ = (arg1); \
typeof(arg2) v2_ = (arg2); \
typeof(arg3) v3_ = (arg3); \
typeof(arg4) v4_ = (arg4); \
typeof(arg5) v5_ = (arg5); \
typeof(arg6) v6_ = (arg6); \
- ALT_CALL_ARG(arg1, 1); \
+ ALT_CALL_ARG(v1_, 1); \
ALT_CALL_ARG(v2_, 2); \
ALT_CALL_ARG(v3_, 3); \
ALT_CALL_ARG(v4_, 4); \
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.17