> On 16 Sep 2020, at 10:28, Jan Kiszka <jan.kis...@siemens.com> wrote:
>
> On 16.09.20 09:12, Oliver Schwartz wrote:
>> SMC calls may modify registers x0 to x3. To make sure the compiler doesn't
>> assume input registers to be constant, also mark these registers as output
>> when used as input.
>> Signed-off-by: Oliver Schwartz <oliver.schwa...@gmx.de>
>> ---
>> hypervisor/arch/arm64/include/asm/smc.h | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>> diff --git a/hypervisor/arch/arm64/include/asm/smc.h
>> b/hypervisor/arch/arm64/include/asm/smc.h
>> index 1a5d5c8..e7b6723 100644
>> --- a/hypervisor/arch/arm64/include/asm/smc.h
>> +++ b/hypervisor/arch/arm64/include/asm/smc.h
>> @@ -28,7 +28,7 @@ static inline long smc_arg1(unsigned long id, unsigned
>> long par1)
>> register unsigned long __par1 asm("r1") = par1;
>> asm volatile ("smc #0\n\t"
>> - : "=r" (__id)
>> + : "=r" (__id), "=r"(__par1)
>> : "r"(__id), "r"(__par1)
>> : "memory", "x2", "x3");
>> @@ -43,7 +43,7 @@ static inline long smc_arg2(unsigned long id, unsigned
>> long par1,
>> register unsigned long __par2 asm("r2") = par2;
>> asm volatile ("smc #0\n\t"
>> - : "=r" (__id)
>> + : "=r" (__id), "=r"(__par1), "=r"(__par2)
>> : "r"(__id), "r"(__par1), "r"(__par2)
>> : "memory", "x3");
>> @@ -62,7 +62,7 @@ static inline long smc_arg5(unsigned long id, unsigned
>> long par1,
>> register unsigned long __par5 asm("r5") = par5;
>> asm volatile ("smc #0\n\t"
>> - : "=r" (__id)
>> + : "=r" (__id), "=r"(__par1), "=r"(__par2), "=r"(__par3)
>> : "r"(__id), "r"(__par1), "r"(__par2), "r"(__par3),
>> "r"(__par4), "r"(__par5)
>> : "memory");
>
> Good catch! We likely have the same issue with our hypercall interface
> (jailhouse_hypercall.h).
>
> We should probably look carefully again at how Linux expresses these
> constraints: linux/include/linux/arm-smccc.h. That appears to me like we need
> "+r" for input/output registers and "=&r" for those that are just input but
> might be clobbered on return.
I must admit that I don’t fully understand the “Constraint Modifier Characters”
chapter in the gcc documentation. Please feel free to modify the patch as
needed.
The 32 bit implementation for smc and hypercall also need a fix.
Oliver
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