From 729772149fcd72379e8118361c43e4632ffa3f01 Mon Sep 17 00:00:00 2001
From: Dave Watson <davejwatson@fb.com>
Date: Tue, 10 Apr 2018 10:55:45 -0700
Subject: 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.
---
 include/libunwind-aarch64.h | 32 ++++++++++++++++++++++++++++----
 src/aarch64/Ginit.c         |  8 ++++----
 src/aarch64/Ginit_local.c   |  2 +-
 3 files changed, 33 insertions(+), 9 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"
diff --git a/src/aarch64/Ginit.c b/src/aarch64/Ginit.c
index 9c4eae82..dec235c8 100644
--- a/src/aarch64/Ginit.c
+++ b/src/aarch64/Ginit.c
@@ -41,7 +41,7 @@ static struct unw_addr_space local_addr_space;
 unw_addr_space_t unw_local_addr_space = &local_addr_space;
 
 static inline void *
-uc_addr (ucontext_t *uc, int reg)
+uc_addr (unw_tdep_context_t *uc, int reg)
 {
   if (reg >= UNW_AARCH64_X0 && reg < UNW_AARCH64_V0)
     return &uc->uc_mcontext.regs[reg];
@@ -54,7 +54,7 @@ uc_addr (ucontext_t *uc, int reg)
 # ifdef UNW_LOCAL_ONLY
 
 HIDDEN void *
-tdep_uc_addr (ucontext_t *uc, int reg)
+tdep_uc_addr (unw_tdep_context_t *uc, int reg)
 {
   return uc_addr (uc, reg);
 }
@@ -104,7 +104,7 @@ access_reg (unw_addr_space_t as, unw_regnum_t reg, unw_word_t *val, int write,
             void *arg)
 {
   unw_word_t *addr;
-  ucontext_t *uc = arg;
+  unw_tdep_context_t *uc = arg;
 
   if (unw_is_fpreg (reg))
     goto badreg;
@@ -133,7 +133,7 @@ static int
 access_fpreg (unw_addr_space_t as, unw_regnum_t reg, unw_fpreg_t *val,
               int write, void *arg)
 {
-  ucontext_t *uc = arg;
+  unw_tdep_context_t *uc = arg;
   unw_fpreg_t *addr;
 
   if (!unw_is_fpreg (reg))
diff --git a/src/aarch64/Ginit_local.c b/src/aarch64/Ginit_local.c
index cd60ca84..69d4ed38 100644
--- a/src/aarch64/Ginit_local.c
+++ b/src/aarch64/Ginit_local.c
@@ -59,7 +59,7 @@ unw_init_local (unw_cursor_t *cursor, unw_context_t *uc)
 }
 
 int
-unw_init_local2 (unw_cursor_t *cursor, ucontext_t *uc, int flag)
+unw_init_local2 (unw_cursor_t *cursor, unw_tdep_context_t *uc, int flag)
 {
   if (!flag)
     {
-- 
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