Implement ARM personality routine in Rust.

Remove the `eh_personality_catch` lang item.
Use a simplified version of `cfg_if!` in libunwind.

2 files changed, 160 insertions, 112 deletions

diff --git a/src/libpanic_unwind/gcc.rs b/src/libpanic_unwind/gcc.rs
index cdf772ad3b8..fdae8f69a9c 100644
--- a/src/libpanic_unwind/gcc.rs
+++ b/src/libpanic_unwind/gcc.rs
@@ -61,6 +61,8 @@ use core::ptr;
 use alloc::boxed::Box;
 
 use unwind as uw;
+use libc::{c_int, uintptr_t};
+use dwarf::eh::{self, EHContext, EHAction};
 
 #[repr(C)]
 struct Exception {
@@ -106,139 +108,184 @@ fn rust_exception_class() -> uw::_Unwind_Exception_Class {
     0x4d4f5a_00_52555354
 }
 
-// All targets, except ARM which uses a slightly different ABI (however, iOS goes here as it uses
-// SjLj unwinding).  Also, 64-bit Windows implementation lives in seh64_gnu.rs
-#[cfg(all(any(target_os = "ios", not(target_arch = "arm"))))]
-pub mod eabi {
-    use unwind as uw;
-    use libc::{c_int, uintptr_t};
-    use dwarf::eh::{EHContext, EHAction, find_eh_action};
 
-    // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
-    // and TargetLowering::getExceptionSelectorRegister() for each architecture,
-    // then mapped to DWARF register numbers via register definition tables
-    // (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
-    // See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
+// Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
+// and TargetLowering::getExceptionSelectorRegister() for each architecture,
+// then mapped to DWARF register numbers via register definition tables
+// (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
+// See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
 
-    #[cfg(target_arch = "x86")]
-    const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
+#[cfg(target_arch = "x86")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
 
-    #[cfg(target_arch = "x86_64")]
-    const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
+#[cfg(target_arch = "x86_64")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
 
-    #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
-    const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
 
-    #[cfg(any(target_arch = "mips", target_arch = "mipsel"))]
-    const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
+#[cfg(any(target_arch = "mips", target_arch = "mipsel"))]
+const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
 
-    #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
-    const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
+#[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
+const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
 
-    // Based on GCC's C and C++ personality routines.  For reference, see:
-    // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
-    // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
-    #[lang = "eh_personality"]
-    #[no_mangle]
-    #[allow(unused)]
-    unsafe extern "C" fn rust_eh_personality(version: c_int,
-                                             actions: uw::_Unwind_Action,
-                                             exception_class: uw::_Unwind_Exception_Class,
-                                             exception_object: *mut uw::_Unwind_Exception,
-                                             context: *mut uw::_Unwind_Context)
-                                             -> uw::_Unwind_Reason_Code {
-        if version != 1 {
-            return uw::_URC_FATAL_PHASE1_ERROR;
-        }
-        let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
-        let mut ip_before_instr: c_int = 0;
-        let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
-        let eh_context = EHContext {
-            // The return address points 1 byte past the call instruction,
-            // which could be in the next IP range in LSDA range table.
-            ip: if ip_before_instr != 0 { ip } else { ip - 1 },
-            func_start: uw::_Unwind_GetRegionStart(context),
-            get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
-            get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
-        };
-        let eh_action = find_eh_action(lsda, &eh_context);
+// The following code is based on GCC's C and C++ personality routines.  For reference, see:
+// https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
+// https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
 
-        if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
-            match eh_action {
-                EHAction::None | EHAction::Cleanup(_) => return uw::_URC_CONTINUE_UNWIND,
-                EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
-                EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR,
-            }
-        } else {
-            match eh_action {
-                EHAction::None => return uw::_URC_CONTINUE_UNWIND,
-                EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
-                    uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
-                    uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
-                    uw::_Unwind_SetIP(context, lpad);
-                    return uw::_URC_INSTALL_CONTEXT;
-                }
-                EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR,
+// The personality routine for most of our targets, except ARM, which has a slightly different ABI
+// (however, iOS goes here as it uses SjLj unwinding).  Also, the 64-bit Windows implementation
+// lives in seh64_gnu.rs
+#[cfg(all(any(target_os = "ios", not(target_arch = "arm"))))]
+#[lang = "eh_personality"]
+#[no_mangle]
+#[allow(unused)]
+unsafe extern "C" fn rust_eh_personality(version: c_int,
+                                         actions: uw::_Unwind_Action,
+                                         exception_class: uw::_Unwind_Exception_Class,
+                                         exception_object: *mut uw::_Unwind_Exception,
+                                         context: *mut uw::_Unwind_Context)
+                                         -> uw::_Unwind_Reason_Code {
+    if version != 1 {
+        return uw::_URC_FATAL_PHASE1_ERROR;
+    }
+    let eh_action = find_eh_action(context);
+    if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
+        match eh_action {
+            EHAction::None | EHAction::Cleanup(_) => return uw::_URC_CONTINUE_UNWIND,
+            EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
+            EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR,
+        }
+    } else {
+        match eh_action {
+            EHAction::None => return uw::_URC_CONTINUE_UNWIND,
+            EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
+                uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
+                uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
+                uw::_Unwind_SetIP(context, lpad);
+                return uw::_URC_INSTALL_CONTEXT;
             }
+            EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR,
         }
     }
-
-    #[cfg(stage0)]
-    #[lang = "eh_personality_catch"]
-    #[no_mangle]
-    pub unsafe extern "C" fn rust_eh_personality_catch(version: c_int,
-                                                       actions: uw::_Unwind_Action,
-                                                       exception_class: uw::_Unwind_Exception_Class,
-                                                       ue_header: *mut uw::_Unwind_Exception,
-                                                       context: *mut uw::_Unwind_Context)
-                                                       -> uw::_Unwind_Reason_Code {
-        rust_eh_personality(version, actions, exception_class, ue_header, context)
-    }
 }
 
-// ARM EHABI uses a slightly different personality routine signature,
-// but otherwise works the same.
+// ARM EHABI personality routine.
+// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
 #[cfg(all(target_arch = "arm", not(target_os = "ios")))]
-pub mod eabi {
-    use unwind as uw;
-    use libc::c_int;
+#[lang = "eh_personality"]
+#[no_mangle]
+unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
+                                         exception_object: *mut uw::_Unwind_Exception,
+                                         context: *mut uw::_Unwind_Context)
+                                        -> uw::_Unwind_Reason_Code {
+    let state = state as c_int;
+    let action = state & uw::_US_ACTION_MASK as c_int;
+    let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
+        // Backtraces on ARM will call the personality routine with
+        // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
+        // we want to continue unwinding the stack, otherwise all our backtraces
+        // would end at __rust_try
+        if state & uw::_US_FORCE_UNWIND as c_int != 0 {
+            return continue_unwind(exception_object, context)
+        }
+        true
+    } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
+        false
+    } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
+        return continue_unwind(exception_object, context);
+    } else {
+        return uw::_URC_FAILURE;
+    };
 
-    extern "C" {
-        fn __gcc_personality_v0(state: uw::_Unwind_State,
-                                ue_header: *mut uw::_Unwind_Exception,
-                                context: *mut uw::_Unwind_Context)
-                                -> uw::_Unwind_Reason_Code;
-    }
+    // The DWARF unwinder assumes that _Unwind_Context holds things like the function
+    // and LSDA pointers, however ARM EHABI places them into the exception object.
+    // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
+    // take only the context pointer, GCC personality routines stash a pointer to exception_object
+    // in the context, using location reserved for ARM's "scratch register" (r12).
+    uw::_Unwind_SetGR(context, uw::UNWIND_POINTER_REG, exception_object as uw::_Unwind_Ptr);
+    // ...A more principled approach would be to provide the full definition of ARM's
+    // _Unwind_Context in our libunwind bindings and fetch the required data from there directly,
+    // bypassing DWARF compatibility functions.
 
-    #[lang = "eh_personality"]
-    #[no_mangle]
-    extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
-                                      ue_header: *mut uw::_Unwind_Exception,
-                                      context: *mut uw::_Unwind_Context)
-                                      -> uw::_Unwind_Reason_Code {
-        unsafe { __gcc_personality_v0(state, ue_header, context) }
+    let eh_action = find_eh_action(context);
+    if search_phase {
+        match eh_action {
+            EHAction::None |
+            EHAction::Cleanup(_) => return continue_unwind(exception_object, context),
+            EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
+            EHAction::Terminate => return uw::_URC_FAILURE,
+        }
+    } else {
+        match eh_action {
+            EHAction::None => return continue_unwind(exception_object, context),
+            EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
+                uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
+                uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
+                uw::_Unwind_SetIP(context, lpad);
+                return uw::_URC_INSTALL_CONTEXT;
+            }
+            EHAction::Terminate => return uw::_URC_FAILURE,
+        }
     }
 
-    #[lang = "eh_personality_catch"]
-    #[no_mangle]
-    pub extern "C" fn rust_eh_personality_catch(state: uw::_Unwind_State,
-                                                ue_header: *mut uw::_Unwind_Exception,
-                                                context: *mut uw::_Unwind_Context)
-                                                -> uw::_Unwind_Reason_Code {
-        // Backtraces on ARM will call the personality routine with
-        // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
-        // we want to continue unwinding the stack, otherwise all our backtraces
-        // would end at __rust_try.
-        if (state as c_int & uw::_US_ACTION_MASK as c_int) ==
-           uw::_US_VIRTUAL_UNWIND_FRAME as c_int &&
-           (state as c_int & uw::_US_FORCE_UNWIND as c_int) == 0 {
-            // search phase
-            uw::_URC_HANDLER_FOUND // catch!
+    // On ARM EHABI the personality routine is responsible for actually
+    // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
+    unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception,
+                              context: *mut uw::_Unwind_Context)
+                              -> uw::_Unwind_Reason_Code {
+        if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
+            uw::_URC_CONTINUE_UNWIND
         } else {
-            // cleanup phase
-            unsafe { __gcc_personality_v0(state, ue_header, context) }
+            uw::_URC_FAILURE
         }
     }
+    // defined in libgcc
+    extern "C" {
+        fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception,
+                                context: *mut uw::_Unwind_Context)
+                                -> uw::_Unwind_Reason_Code;
+    }
+}
+
+unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> EHAction {
+    let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
+    let mut ip_before_instr: c_int = 0;
+    let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
+    let eh_context = EHContext {
+        // The return address points 1 byte past the call instruction,
+        // which could be in the next IP range in LSDA range table.
+        ip: if ip_before_instr != 0 { ip } else { ip - 1 },
+        func_start: uw::_Unwind_GetRegionStart(context),
+        get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
+        get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
+    };
+    eh::find_eh_action(lsda, &eh_context)
+}
+
+// *** Delete after a new snapshot ***
+#[cfg(all(stage0, any(target_os = "ios", not(target_arch = "arm"))))]
+#[lang = "eh_personality_catch"]
+#[no_mangle]
+pub unsafe extern "C" fn rust_eh_personality_catch(version: c_int,
+                                                    actions: uw::_Unwind_Action,
+                                                    exception_class: uw::_Unwind_Exception_Class,
+                                                    ue_header: *mut uw::_Unwind_Exception,
+                                                    context: *mut uw::_Unwind_Context)
+                                                    -> uw::_Unwind_Reason_Code {
+    rust_eh_personality(version, actions, exception_class, ue_header, context)
+}
+
+// *** Delete after a new snapshot ***
+#[cfg(all(stage0, target_arch = "arm", not(target_os = "ios")))]
+#[lang = "eh_personality_catch"]
+#[no_mangle]
+pub unsafe extern "C" fn rust_eh_personality_catch(state: uw::_Unwind_State,
+                                                    ue_header: *mut uw::_Unwind_Exception,
+                                                    context: *mut uw::_Unwind_Context)
+                                                    -> uw::_Unwind_Reason_Code {
+    rust_eh_personality(state, ue_header, context)
 }
 
 // See docs in the `unwind` module.
diff --git a/src/libpanic_unwind/seh64_gnu.rs b/src/libpanic_unwind/seh64_gnu.rs
index 7dc428871b3..3642e248895 100644
--- a/src/libpanic_unwind/seh64_gnu.rs
+++ b/src/libpanic_unwind/seh64_gnu.rs
@@ -81,6 +81,7 @@ pub unsafe fn cleanup(ptr: *mut u8) -> Box<Any + Send> {
 // This is considered acceptable, because the behavior of throwing exceptions
 // through a C ABI boundary is undefined.
 
+// *** Delete after a new snapshot ***
 #[cfg(stage0)]
 #[lang = "eh_personality_catch"]
 #[cfg(not(test))]