Hi Julien,
Julien Grall writes:
> At the moment, the user should save x30/lr if it cares about it.
>
> Follow-up patches will introduce more use of putn in place where lr
> should be preserved.
>
> Furthermore, any user of putn should also move the value to register x0
> if it was stored in a different register.
>
> For convenience, a new macro is introduced to print a given register.
> The macro will take care for us to move the value to x0 and also
> preserve lr.
>
> Lastly the new macro is used to replace all the callsite of putn. This
> will simplify rework/review later on.
>
> Note that CurrentEL is now stored in x5 instead of x4 because the latter
> will be clobbered by the macro print_reg.
>
> Signed-off-by: Julien Grall <julien.gr...@arm.com>
> ---
> xen/arch/arm/arm64/head.S | 29 ++++++++++++++++++++++-------
> 1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index 84e26582c4..9142b4a774 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -90,8 +90,25 @@
> bl puts ; \
> mov lr, x3 ; \
> RODATA_STR(98, _s)
> +
> +/*
> + * Macro to print the value of register \xb
> + *
> + * Clobbers x0 - x4
> + */
Despite its name, this macro can't print x4. I would recommend adding at
least comment about this. Static assertion would be even better, but
looks like we don't have them for asm code.
> +.macro print_reg xb
> + mov x4, lr
> + mov x0, \xb
> + bl putn
> + mov lr, x4
> +.endm
> +
> #else /* CONFIG_EARLY_PRINTK */
> #define PRINT(s)
> +
> +.macro print_reg xb
> +.endm
> +
> #endif /* !CONFIG_EARLY_PRINTK */
>
> /* Load the physical address of a symbol into xb */
> @@ -304,22 +321,20 @@ GLOBAL(init_secondary)
> #ifdef CONFIG_EARLY_PRINTK
> ldr x23, =EARLY_UART_BASE_ADDRESS /* x23 := UART base address */
> PRINT("- CPU ")
> - mov x0, x24
> - bl putn
> + print_reg x24
> PRINT(" booting -\r\n")
> #endif
>
> common_start:
>
> PRINT("- Current EL ")
> - mrs x4, CurrentEL
> - mov x0, x4
> - bl putn
> + mrs x5, CurrentEL
> + print_reg x5
> PRINT(" -\r\n")
>
> /* Are we in EL2 */
> - cmp x4, #PSR_MODE_EL2t
> - ccmp x4, #PSR_MODE_EL2h, #0x4, ne
> + cmp x5, #PSR_MODE_EL2t
> + ccmp x5, #PSR_MODE_EL2h, #0x4, ne
> b.eq el2 /* Yes */
>
> /* OK, we're boned. */
--
Best regards, Volodymyr Babchuk
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