[PATCH 02/10] mach: Define MACHINE_THREAD_STATE_SETUP_CALL

[Sergey Bugaev]

The existing two macros, MACHINE_THREAD_STATE_SET_PC and
MACHINE_THREAD_STATE_SET_SP, can be used to set program counter and the
stack pointer registers in a machine-specific thread state structure.

Useful as it is, this may not be enough to set up the thread to make a
function call, because the machine-specific ABI may impose additional
requirements. In particular, x86_64 ABI requires that upon function
entry, the stack pointer is 8 less than 16-byte aligned (sp & 15 == 8).

To deal with this, introduce a new macro,
MACHINE_THREAD_STATE_SETUP_CALL (), which sets both stack and
instruction pointers, and also applies any machine-specific requirements
to make a valid function call. The default implementation simply
forwards to MACHINE_THREAD_STATE_SET_PC and MACHINE_THREAD_STATE_SET_SP,
but on x86_64 we additionally align the stack pointer.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
Any ideas for a better name than PTR_ALIGN_DOWN_8_16?

 sysdeps/mach/thread_state.h     |  9 +++++++++
 sysdeps/mach/x86/thread_state.h | 13 +++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/sysdeps/mach/thread_state.h b/sysdeps/mach/thread_state.h
index 9fa3d4e1..431aaf82 100644
--- a/sysdeps/mach/thread_state.h
+++ b/sysdeps/mach/thread_state.h
@@ -38,6 +38,15 @@
 #endif
 #endif
 
+/* Set up the thread state to call the given function on the given state.
+   Dependning on architecture, this may imply more than just setting PC
+   and SP.  */
+#ifndef MACHINE_THREAD_STATE_SETUP_CALL
+#define MACHINE_THREAD_STATE_SETUP_CALL(ts, stack, size, func) \
+  (MACHINE_THREAD_STATE_SET_PC (ts, func), \
+   MACHINE_THREAD_STATE_SET_SP (ts, stack, size))
+#endif
+
 /* This copies architecture-specific bits from the current thread to the new
    thread state.  */
 #ifndef MACHINE_THREAD_STATE_FIX_NEW
diff --git a/sysdeps/mach/x86/thread_state.h b/sysdeps/mach/x86/thread_state.h
index 5be0bec1..8c419515 100644
--- a/sysdeps/mach/x86/thread_state.h
+++ b/sysdeps/mach/x86/thread_state.h
@@ -20,6 +20,7 @@
 #define _MACH_X86_THREAD_STATE_H 1
 
 #include <mach/machine/thread_status.h>
+#include <libc-pointer-arith.h>
 
 /* This lets the kernel define segments for a new thread.  */
 #define MACHINE_NEW_THREAD_STATE_FLAVOR        i386_THREAD_STATE
@@ -54,6 +55,18 @@ struct machine_thread_all_state
     struct i386_float_state fpu;
   };
 
+#ifdef __x86_64__
+/* We're setting up the stack to perform a function call.  On function entry,
+   the stack pointer must be 8 bytes less than 16-aligned.  */
+#define PTR_ALIGN_DOWN_8_16(ptr)                                             \
+ ({ uintptr_t __ptr = PTR_ALIGN_DOWN (ptr, 8);                               \
+    PTR_IS_ALIGNED (__ptr, 16) ? (__ptr - 8) : __ptr; })
+
+#define MACHINE_THREAD_STATE_SETUP_CALL(ts, stack, size, func)               \
+  ((ts)->SP = PTR_ALIGN_DOWN_8_16 ((uintptr_t) (stack) + (size)),            \
+   (ts)->PC = (uintptr_t) func)
+#endif
+
 #include <sysdeps/mach/thread_state.h>
 
 #endif /* mach/x86/thread_state.h */
-- 
2.40.1