[PATCH v4 10/20] powerpc: Use common syscall handler type

[Rohan McLure]

> On 12 Sep 2022, at 8:56 pm, Nicholas Piggin <npiggin at gmail.com> wrote:
> 
> On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:
>> Cause syscall handlers to be typed as follows when called indirectly
>> throughout the kernel.
>> 
>> typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
>>                           unsigned long, unsigned long, unsigned long);
> 
> The point is... better type checking?
> 
>> 
>> Since both 32 and 64-bit abis allow for at least the first six
>> machine-word length parameters to a function to be passed by registers,
>> even handlers which admit fewer than six parameters may be viewed as
>> having the above type.
>> 
>> Fixup comparisons in VDSO to avoid pointer-integer comparison. Introduce
>> explicit cast on systems with SPUs.
>> 
>> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
>> ---
>> V1 -> V2: New patch.
>> V2 -> V3: Remove unnecessary cast from const syscall_fn to syscall_fn
>> ---
>> arch/powerpc/include/asm/syscall.h          | 7 +++++--
>> arch/powerpc/include/asm/syscalls.h         | 1 +
>> arch/powerpc/kernel/systbl.c                | 6 +++---
>> arch/powerpc/kernel/vdso.c                  | 4 ++--
>> arch/powerpc/platforms/cell/spu_callbacks.c | 6 +++---
>> 5 files changed, 14 insertions(+), 10 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
>> index 25fc8ad9a27a..d2a8dfd5de33 100644
>> --- a/arch/powerpc/include/asm/syscall.h
>> +++ b/arch/powerpc/include/asm/syscall.h
>> @@ -14,9 +14,12 @@
>> #include <linux/sched.h>
>> #include <linux/thread_info.h>
>> 
>> +typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
>> +			   unsigned long, unsigned long, unsigned long);
>> +
>> /* ftrace syscalls requires exporting the sys_call_table */
>> -extern const unsigned long sys_call_table[];
>> -extern const unsigned long compat_sys_call_table[];
>> +extern const syscall_fn sys_call_table[];
>> +extern const syscall_fn compat_sys_call_table[];
> 
> Ah you constify it in this patch. I think the previous patch should have
> kept the const, and it should keep the unsigned long type rather than
> use void *. Either that or do this patch first.
> 
>> static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>> {
>> diff --git a/arch/powerpc/include/asm/syscalls.h b/arch/powerpc/include/asm/syscalls.h
>> index 91417dee534e..e979b7593d2b 100644
>> --- a/arch/powerpc/include/asm/syscalls.h
>> +++ b/arch/powerpc/include/asm/syscalls.h
>> @@ -8,6 +8,7 @@
>> #include <linux/types.h>
>> #include <linux/compat.h>
>> 
>> +#include <asm/syscall.h>
>> #ifdef CONFIG_PPC64
>> #include <asm/syscalls_32.h>
>> #endif
> 
> Is this necessary or should be in another patch?

Good spot. This belongs in the patch that produces systbl.c.

> 
>> diff --git a/arch/powerpc/kernel/systbl.c b/arch/powerpc/kernel/systbl.c
>> index 99ffdfef6b9c..b88a9c2a1f50 100644
>> --- a/arch/powerpc/kernel/systbl.c
>> +++ b/arch/powerpc/kernel/systbl.c
>> @@ -21,10 +21,10 @@
>> #define __SYSCALL(nr, entry) [nr] = __powerpc_##entry,
>> #define __powerpc_sys_ni_syscall	sys_ni_syscall
>> #else
>> -#define __SYSCALL(nr, entry) [nr] = entry,
>> +#define __SYSCALL(nr, entry) [nr] = (void *) entry,
>> #endif
> 
> Also perhaps this should have been in the prior pach and this pach
> should change the cast from void to syscall_fn ?

This cast to (void *) kicks in when casting functions with six or fewer
parameters to six-parameter type accepting and returning u64. Sadly I can’t
find a way to avoid -Wcast-function-type even with (__force syscall_fn) short
of an ugly casti to void* here. Any suggestions?

> 
>> 
>> -void *sys_call_table[] = {
>> +const syscall_fn sys_call_table[] = {
>> #ifdef CONFIG_PPC64
>> #include <asm/syscall_table_64.h>
>> #else
>> @@ -35,7 +35,7 @@ void *sys_call_table[] = {
>> #ifdef CONFIG_COMPAT
>> #undef __SYSCALL_WITH_COMPAT
>> #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
>> -void *compat_sys_call_table[] = {
>> +const syscall_fn compat_sys_call_table[] = {
>> #include <asm/syscall_table_32.h>
>> };
>> #endif /* CONFIG_COMPAT */
>> diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
>> index 0da287544054..080c9e7de0c0 100644
>> --- a/arch/powerpc/kernel/vdso.c
>> +++ b/arch/powerpc/kernel/vdso.c
>> @@ -313,10 +313,10 @@ static void __init vdso_setup_syscall_map(void)
>> 	unsigned int i;
>> 
>> 	for (i = 0; i < NR_syscalls; i++) {
>> -		if (sys_call_table[i] != (unsigned long)&sys_ni_syscall)
>> +		if (sys_call_table[i] != (void *)&sys_ni_syscall)
>> 			vdso_data->syscall_map[i >> 5] |= 0x80000000UL >> (i & 0x1f);
>> 		if (IS_ENABLED(CONFIG_COMPAT) &&
>> -		    compat_sys_call_table[i] != (unsigned long)&sys_ni_syscall)
>> +		    compat_sys_call_table[i] != (void *)&sys_ni_syscall)
> 
> Also these.
> 
> Thanks,
> Nick
> 
>> 			vdso_data->compat_syscall_map[i >> 5] |= 0x80000000UL >> (i & 0x1f);
>> 	}
>> }
>> diff --git a/arch/powerpc/platforms/cell/spu_callbacks.c b/arch/powerpc/platforms/cell/spu_callbacks.c
>> index fe0d8797a00a..e780c14c5733 100644
>> --- a/arch/powerpc/platforms/cell/spu_callbacks.c
>> +++ b/arch/powerpc/platforms/cell/spu_callbacks.c
>> @@ -34,15 +34,15 @@
>>  *	mbind, mq_open, ipc, ...
>>  */
>> 
>> -static void *spu_syscall_table[] = {
>> +static const syscall_fn spu_syscall_table[] = {
>> #define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
>> -#define __SYSCALL(nr, entry) [nr] = entry,
>> +#define __SYSCALL(nr, entry) [nr] = (void *) entry,
>> #include <asm/syscall_table_spu.h>
>> };
>> 
>> long spu_sys_callback(struct spu_syscall_block *s)
>> {
>> -	long (*syscall)(u64 a1, u64 a2, u64 a3, u64 a4, u64 a5, u64 a6);
>> +	syscall_fn syscall;
>> 
>> 	if (s->nr_ret >= ARRAY_SIZE(spu_syscall_table)) {
>> 		pr_debug("%s: invalid syscall #%lld", __func__, s->nr_ret);
>> -- 
>> 2.34.1