On 12 Sep 2022, at 8:56 pm, Nicholas Piggin [off-list ref] wrote:

On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:

quoted

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?

quoted

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 <redacted>
---
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.

quoted

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.

quoted

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?

quoted

-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

quoted

			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