[RFC PATCH] arm64: signal: Make parse_user_sigframe() independent of rt_sigframe layout

[Dave Martin]

ILP32 support uses the same struct sigcontext as the native ABI
(i.e., LP64), but a different layout for the rest of the signal
frame (since siginfo_t and ucontext_t are both ABI-dependent).

Since the purpose of parse_user_sigframe() is really to parse
sigcontext and not the whole signal frame, the function does not
need to depend on the layout of rt_sigframe -- the only purpose of
the rt_sigframe pointer is for use as a base to measure the signal
frame size.

So, this patch renames the function to parse_user_sigcontext() and
makes the sigframe base pointer generic.  ABI-specific parsers that
share the same sigcontext definition can then call it.

To minimise churn in this patch, the native LP64 parser is retained
under the old name, but becomes a call to parse_user_sigconext().
It may make sense instead to fold this into its restore_sigframe(),
depending on how ILP32 support is integrated.

Suggested-by: Yury Norov <ynorov at caviumnetworks.com>
Signed-off-by: Dave Martin <Dave.Martin at arm.com>
---

This patch depends on [1], which does not appear to be applied yet.

[1] [PATCH] arm64: signal: Allow expansion of the signal frame                  http://lists.infradead.org/pipermail/linux-arm-kernel/2017-June/514699.html

 arch/arm64/kernel/signal.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index e47cd3a..a189321 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -223,16 +223,16 @@ struct user_ctxs {
 	struct fpsimd_context __user *fpsimd;
 };
 
-static int parse_user_sigframe(struct user_ctxs *user,
-			       struct rt_sigframe __user *sf)
+static int parse_user_sigcontext(struct user_ctxs *user,
+				 struct sigcontext __user const *sc,
+				 void __user const *sigframe_base)
 {
-	struct sigcontext __user *const sc = &sf->uc.uc_mcontext;
 	struct _aarch64_ctx __user *head;
 	char __user *base = (char __user *)&sc->__reserved;
 	size_t offset = 0;
 	size_t limit = sizeof(sc->__reserved);
 	bool have_extra_context = false;
-	char const __user *const sfp = (char const __user *)sf;
+	char const __user *const sfp = (char const __user *)sigframe_base;
 
 	user->fpsimd = NULL;
 
@@ -366,6 +366,12 @@ static int parse_user_sigframe(struct user_ctxs *user,
 	return -EINVAL;
 }
 
+static int parse_user_sigframe(struct user_ctxs *user,
+			       struct rt_sigframe __user const *sf)
+{
+	return parse_user_sigcontext(user, &sf->uc.uc_mcontext, sf);
+}
+
 static int restore_sigframe(struct pt_regs *regs,
 			    struct rt_sigframe __user *sf)
 {
-- 
2.1.4