The current code in ALT_CALL_ARG() won't successfully workaround the clang code-generation issue if the arg parameter has a size that's not a power of 2. While there are no such sized parameters at the moment, improve the workaround to also be effective when such sizes are used. Instead of using a union with a long, add the necessary padding so that the resulting struct always has the same size as a register, and let the compiler zero-initialize the padding. Reported-by: Alejandro Vallejo <alejandro.vallejo@cloud.com> Suggested-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> --- xen/arch/x86/include/asm/alternative.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/xen/arch/x86/include/asm/alternative.h b/xen/arch/x86/include/asm/alternative.h index XXXXXXX..XXXXXXX 100644 --- a/xen/arch/x86/include/asm/alternative.h +++ b/xen/arch/x86/include/asm/alternative.h @@ -XXX,XX +XXX,XX @@ extern void alternative_branches(void); * https://github.com/llvm/llvm-project/issues/82598 */ #define ALT_CALL_ARG(arg, n) \ - register union { \ - typeof(arg) e[sizeof(long) / sizeof(arg)]; \ - unsigned long r; \ + register struct { \ + typeof(arg) e; \ + char pad[sizeof(void *) - sizeof(arg)]; \ } a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \ - .e[0] = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); })\ + .e = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); }) \ } #else #define ALT_CALL_ARG(arg, n) \ -- 2.45.2 The current code in ALT_CALL_ARG() won't successfully workaround the clang code-generation issue if the arg parameter has a size that's not a power of 2. While there are no such sized parameters at the moment, improve the workaround to also be effective when such sizes are used. Instead of using a union with a long use an unsigned long that's first initialized to 0 and afterwards set to the argument value. Reported-by: Alejandro Vallejo <alejandro.vallejo@cloud.com> Suggested-by: Alejandro Vallejo <alejandro.vallejo@cloud.com> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> --- xen/arch/x86/include/asm/alternative.h | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/xen/arch/x86/include/asm/alternative.h b/xen/arch/x86/include/asm/alternative.h index XXXXXXX..XXXXXXX 100644 --- a/xen/arch/x86/include/asm/alternative.h +++ b/xen/arch/x86/include/asm/alternative.h @@ -XXX,XX +XXX,XX @@ extern void alternative_branches(void); * https://github.com/llvm/llvm-project/issues/12579 * https://github.com/llvm/llvm-project/issues/82598 */ -#define ALT_CALL_ARG(arg, n) \ - register union { \ - typeof(arg) e[sizeof(long) / sizeof(arg)]; \ - unsigned long r; \ - } a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \ - .e[0] = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); })\ - } +#define ALT_CALL_ARG(arg, n) \ + register unsigned long a ## n ## _ asm ( ALT_CALL_arg ## n ) = ({ \ + unsigned long tmp = 0; \ + *(typeof(arg) *)&tmp = (arg); \ + BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); \ + tmp; \ + }) #else #define ALT_CALL_ARG(arg, n) \ register typeof(arg) a ## n ## _ asm ( ALT_CALL_arg ## n ) = \ -- 2.45.2