On 10.02.2026 12:15, Andrew Cooper wrote: > On 07/10/2025 4:58 pm, Jan Beulich wrote: >> On 04.10.2025 00:53, Andrew Cooper wrote: >>> FRED and IDT differ by a Supervisor Token on the base of the shstk. This >>> means that switch_stack_and_jump() needs to discard one extra word when FRED >>> is active. >>> >>> Fix a typo in the parameter name, which should be shstk_base. >>> >>> Signed-off-by: Andrew Cooper <[email protected]> >>> Reviewed-by: Jan Beulich <[email protected]> >>> --- >>> CC: Jan Beulich <[email protected]> >>> CC: Roger Pau Monné <[email protected]> >>> >>> Leave as $%c. Otherwise it doesn't assemble correctly presented with >>> $$24568 >>> to parse as an instruction immediate. >> I don't follow. Where would the 2nd $ come from if you write ... >> >>> --- a/xen/arch/x86/include/asm/current.h >>> +++ b/xen/arch/x86/include/asm/current.h >>> @@ -154,7 +154,9 @@ unsigned long get_stack_dump_bottom (unsigned long sp); >>> "rdsspd %[ssp];" \ >>> "cmp $1, %[ssp];" \ >>> "je .L_shstk_done.%=;" /* CET not active? Skip. */ \ >>> - "mov $%c[skstk_base], %[val];" \ >>> + ALTERNATIVE("mov $%c[shstk_base], %[val];", \ >>> + "mov $%c[shstk_base] + 8, %[val];", \ >>> + X86_FEATURE_XEN_FRED) \ >> ALTERNATIVE("mov %[shstk_base], %[val];", \ >> "mov %[shstk_base] + 8, %[val];", \ >> X86_FEATURE_XEN_FRED) \ > > I find this feedback completely uncharacteristic. You always goes out > of your way to hide % inside macros to prohibit non-register operands. > > This is exactly the same, except to force an immediate operand, so the > length of the two instructions is the same.
Thinking about it more, are you perhaps referring to assembler macros? There indeed I prefer to have the % inside the macros; the same may go for $ there, but I don't think we had the need so far. For inline assembly the situation is different: The compiler emits the % (and also the $), unless special modifiers are used. It wouldn't even occur to me to ask that we use %%%V[val] for a register operand. That really is the register equivalent of the $%c[val] that you use above. Jan
