Introduce a native-only unwinder build.

Currently libunwind is built to support cross-unwinding [1] by default, which
requires the buffers unw_context_t and unw_cursor_t to be large enough to hold
the vritual register set (VRS) of any supported architecture. This is not
desirable for some platforms where the stack usage of the unwinder needs
to be kept to a minimum (e.g. bare-metal targets). The current patch introduces
a native-only (-DLIBUNWIND_ENABLE_CROSS_UNWINDING=OFF) unwinder variant that
adopts strict sizes for the buffers unw_context_t and unw_cursor_t depending
on the target architecture.

[1] http://www.nongnu.org/libunwind/man/libunwind(3).html#section_4

Change-Id: I380fff9a56c16a0fc520e3b1d8454a34b4a48373
llvm-svn: 270692

2 files changed, 41 insertions, 2 deletions

diff --git a/libunwind/include/__libunwind_config.h b/libunwind/include/__libunwind_config.h
index 63393d3058e..099d133e744 100644
--- a/libunwind/include/__libunwind_config.h
+++ b/libunwind/include/__libunwind_config.h
@@ -17,4 +17,43 @@
 #define _LIBUNWIND_ARM_EHABI 0
 #endif
 
+#if defined(_LIBUNWIND_IS_NATIVE_ONLY)
+# if defined(__i386__)
+#  define _LIBUNWIND_TARGET_I386 1
+#  define _LIBUNWIND_CONTEXT_SIZE 8
+#  define _LIBUNWIND_CURSOR_SIZE 19
+# elif defined(__x86_64__)
+#  define _LIBUNWIND_TARGET_X86_64 1
+#  define _LIBUNWIND_CONTEXT_SIZE 21
+#  define _LIBUNWIND_CURSOR_SIZE 33
+# elif defined(__ppc__)
+#  define _LIBUNWIND_TARGET_PPC 1
+#  define _LIBUNWIND_CONTEXT_SIZE 117
+#  define _LIBUNWIND_CURSOR_SIZE 128
+# elif defined(__aarch64__)
+#  define _LIBUNWIND_TARGET_AARCH64 1
+#  define _LIBUNWIND_CONTEXT_SIZE 66
+#  define _LIBUNWIND_CURSOR_SIZE 78
+# elif defined(__arm__)
+#  define _LIBUNWIND_TARGET_ARM 1
+#  define _LIBUNWIND_CONTEXT_SIZE 60
+#  define _LIBUNWIND_CURSOR_SIZE 67
+# elif defined(__or1k__)
+#  define _LIBUNWIND_TARGET_OR1K 1
+#  define _LIBUNWIND_CONTEXT_SIZE 16
+#  define _LIBUNWIND_CURSOR_SIZE 28
+# else
+#  error "Unsupported architecture."
+# endif
+#else // !_LIBUNWIND_IS_NATIVE_ONLY
+# define _LIBUNWIND_TARGET_I386 1
+# define _LIBUNWIND_TARGET_X86_64 1
+# define _LIBUNWIND_TARGET_PPC 1
+# define _LIBUNWIND_TARGET_AARCH64 1
+# define _LIBUNWIND_TARGET_ARM 1
+# define _LIBUNWIND_TARGET_OR1K 1
+# define _LIBUNWIND_CONTEXT_SIZE 128
+# define _LIBUNWIND_CURSOR_SIZE 140
+#endif // _LIBUNWIND_IS_NATIVE_ONLY
+
 #endif // ____LIBUNWIND_CONFIG_H__
diff --git a/libunwind/include/libunwind.h b/libunwind/include/libunwind.h
index 6045becc01a..c5b9633b150 100644
--- a/libunwind/include/libunwind.h
+++ b/libunwind/include/libunwind.h
@@ -46,12 +46,12 @@ enum {
 };
 
 struct unw_context_t {
-  uint64_t data[128];
+  uint64_t data[_LIBUNWIND_CONTEXT_SIZE];
 };
 typedef struct unw_context_t unw_context_t;
 
 struct unw_cursor_t {
-  uint64_t data[140];
+  uint64_t data[_LIBUNWIND_CURSOR_SIZE];
 };
 typedef struct unw_cursor_t unw_cursor_t;