arm: Add compile-time asserts for siginfo_t offsets

To help catch ABI breaks at compile-time, add compile-time assertions to
verify the siginfo_t layout.

This could have caught that we cannot portably add 64-bit integers to
siginfo_t on 32-bit architectures like Arm before reaching -next:
https://lkml.kernel.org/r/20210422191823.79012-1-elver@google.com

Link: https://lkml.kernel.org/r/20210429190734.624918-2-elver@google.com
Link: https://lkml.kernel.org/r/20210505141101.11519-2-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/87y2a7xx9q.fsf_-_@disp2133
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index a3a38d0a4c853332102aefd01c02b0967e0ccc3f..7ef453e8a96ff1e245d21f689def9850811d8caa 100644 (file)
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -725,3 +725,40 @@ asmlinkage void do_rseq_syscall(struct pt_regs *regs)
        rseq_syscall(regs);
 }
 #endif
+
+/*
+ * Compile-time assertions for siginfo_t offsets. Check NSIG* as well, as
+ * changes likely come with new fields that should be added below.
+ */
+static_assert(NSIGILL  == 11);
+static_assert(NSIGFPE  == 15);
+static_assert(NSIGSEGV == 9);
+static_assert(NSIGBUS  == 5);
+static_assert(NSIGTRAP == 6);
+static_assert(NSIGCHLD == 6);
+static_assert(NSIGSYS  == 2);
+static_assert(offsetof(siginfo_t, si_signo)    == 0x00);
+static_assert(offsetof(siginfo_t, si_errno)    == 0x04);
+static_assert(offsetof(siginfo_t, si_code)     == 0x08);
+static_assert(offsetof(siginfo_t, si_pid)      == 0x0c);
+static_assert(offsetof(siginfo_t, si_uid)      == 0x10);
+static_assert(offsetof(siginfo_t, si_tid)      == 0x0c);
+static_assert(offsetof(siginfo_t, si_overrun)  == 0x10);
+static_assert(offsetof(siginfo_t, si_status)   == 0x14);
+static_assert(offsetof(siginfo_t, si_utime)    == 0x18);
+static_assert(offsetof(siginfo_t, si_stime)    == 0x1c);
+static_assert(offsetof(siginfo_t, si_value)    == 0x14);
+static_assert(offsetof(siginfo_t, si_int)      == 0x14);
+static_assert(offsetof(siginfo_t, si_ptr)      == 0x14);
+static_assert(offsetof(siginfo_t, si_addr)     == 0x0c);
+static_assert(offsetof(siginfo_t, si_addr_lsb) == 0x10);
+static_assert(offsetof(siginfo_t, si_lower)    == 0x14);
+static_assert(offsetof(siginfo_t, si_upper)    == 0x18);
+static_assert(offsetof(siginfo_t, si_pkey)     == 0x14);
+static_assert(offsetof(siginfo_t, si_perf_data)        == 0x10);
+static_assert(offsetof(siginfo_t, si_perf_type)        == 0x14);
+static_assert(offsetof(siginfo_t, si_band)     == 0x0c);
+static_assert(offsetof(siginfo_t, si_fd)       == 0x10);
+static_assert(offsetof(siginfo_t, si_call_addr)        == 0x0c);
+static_assert(offsetof(siginfo_t, si_syscall)  == 0x10);
+static_assert(offsetof(siginfo_t, si_arch)     == 0x14);