aarch64: tune down size of unw_context_t and unw_cursor_t (#71)

aarch64 defines a huge __reserved field in sigcontext.  Cut it down
to only the used FP fields.

unw_cursor_t can also be cut down a bit, while still maintaining some reserved space.

1 files changed, 28 insertions, 4 deletions

diff --git a/include/libunwind-aarch64.h b/include/libunwind-aarch64.h
index 85812e15..11e2a9c1 100644
--- a/include/libunwind-aarch64.h
+++ b/include/libunwind-aarch64.h
@@ -44,9 +44,13 @@ extern "C" {
    leaving some slack for future expansion.  Changing this value will
    require recompiling all users of this library.  Stack allocation is
    relatively cheap and unwind-state copying is relatively rare, so we
-   want to err on making it rather too big than too small.  */
+   want to err on making it rather too big than too small.
 
-#define UNW_TDEP_CURSOR_LEN     512
+   Calculation is regs used (64 + 34) * 2 + 40 (bytes of rest of
+   cursor) + padding
+*/
+
+#define UNW_TDEP_CURSOR_LEN     250
 
 typedef uint64_t unw_word_t;
 typedef int64_t unw_sword_t;
@@ -169,8 +173,28 @@ typedef struct unw_tdep_save_loc
 unw_tdep_save_loc_t;
 
 
-/* On AArch64, we can directly use ucontext_t as the unwind context.  */
-typedef ucontext_t unw_tdep_context_t;
+/* On AArch64, we can directly use ucontext_t as the unwind context,
+ * however, the __reserved struct is quite large: tune it down to only
+ * the necessary used fields.  */
+
+struct unw_sigcontext
+  {
+	uint64_t fault_address;
+	uint64_t regs[31];
+	uint64_t sp;
+	uint64_t pc;
+	uint64_t pstate;
+	uint8_t __reserved[(34 * 8)] __attribute__((__aligned__(16)));
+};
+
+typedef struct
+  {
+	unsigned long uc_flags;
+	struct ucontext *uc_link;
+	stack_t uc_stack;
+	__sigset_t uc_sigmask;
+	struct unw_sigcontext uc_mcontext;
+  } unw_tdep_context_t;
 
 #include "libunwind-common.h"
 #include "libunwind-dynamic.h"