[PATCH v2 01/10] arm64: pt_regs: assert pt_regs is a multiple of 16 bytes

[Mark Rutland]

To ensure that the stack is correctly aligned when branching to C code,
we require that struct pt_regs is a multiple of 16 bytes, as noted in a
comment.

Add an explicit assertion for this, so that any accidental violation of
this requirement will be caught by the compiler.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Reviewed-by: Mark Brown <broonie at kernel.org>
Reviewed-by: Miroslav Benes <mbenes at suse.cz>
Reviewed-by: Puranjay Mohan <puranjay12 at gmail.com>
Cc: Ard Biesheuvel <ardb at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Josh Poimboeuf <jpoimboe at kernel.org>
Cc: Kalesh Singh <kaleshsingh at google.com>
Cc: Madhavan T. Venkataraman <madvenka at linux.microsoft.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Will Deacon <will at kernel.org>
---
 arch/arm64/include/asm/ptrace.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 0abe975d68a8e..10eca3a3fed49 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -149,8 +149,7 @@ static inline unsigned long pstate_to_compat_psr(const unsigned long pstate)
 
 /*
  * This struct defines the way the registers are stored on the stack during an
- * exception. Note that sizeof(struct pt_regs) has to be a multiple of 16 (for
- * stack alignment). struct user_pt_regs must form a prefix of struct pt_regs.
+ * exception. struct user_pt_regs must form a prefix of struct pt_regs.
  */
 struct pt_regs {
 	union {
@@ -180,6 +179,9 @@ struct pt_regs {
 	u64 exit_rcu;
 };
 
+/* For correct stack alignment, pt_regs has to be a multiple of 16 bytes. */
+static_assert(IS_ALIGNED(sizeof(struct pt_regs), 16));
+
 static inline bool in_syscall(struct pt_regs const *regs)
 {
 	return regs->syscallno != NO_SYSCALL;
-- 
2.30.2