strace of arm binaries on arm64

[Dmitry V. Levin]

On Wed, Feb 26, 2014 at 02:01:51PM -0800, enh wrote:
> i notice that the decoding of sigaltstack's struct stack_t is wrong on
> arm64 for a 32-bit process. looking at print_stack_t in strace, i
> don't understand how this works for x86/x86_64 --- the first field is
> a void*. so i'm a bit confused about how i should go about fixing this
> for arm/arm64. anyone have a clue to spare?

This is a demonstration why current multiarch approach is unreliable: every
structure containing members whose size differs between personalities has
to be open-coded.  In case of stack_t, the fix is likely to be this:

--- a/signal.c
+++ b/signal.c
@@ -1084,10 +1084,33 @@ static void
 print_stack_t(struct tcb *tcp, unsigned long addr)
 {
 	stack_t ss;
+	int r;
 
 	if (!addr) {
 		tprints("NULL");
-	} else if (umove(tcp, addr, &ss) < 0) {
+		return;
+	}
+
+#if SUPPORTED_PERSONALITIES > 1 && SIZEOF_LONG > 4
+	if (current_wordsize != sizeof(ss.ss_sp) && current_wordsize == 4) {
+		struct {
+			uint32_t ss_sp;
+			int32_t ss_flags;
+			uint32_t ss_size;
+		} ss32;
+		r = umove(tcp, addr, &ss32);
+		if (r >= 0) {
+			memset(&ss, 0, sizeof(ss));
+			ss.ss_sp = (void*)(unsigned long) ss32.ss_sp;
+			ss.ss_flags = ss32.ss_flags;
+			ss.ss_size = (unsigned long) ss32.ss_size;
+		}
+	} else
+#endif
+	{
+		r = umove(tcp, addr, &ss);
+	}
+	if (r < 0) {
 		tprintf("%#lx", addr);
 	} else {
 		tprintf("{ss_sp=%#lx, ss_flags=", (unsigned long) ss.ss_sp);


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