https://gcc.gnu.org/g:c4e90a24d0ac36f8daa08ecac127461a7e294d10
commit r15-4164-gc4e90a24d0ac36f8daa08ecac127461a7e294d10
Author: Olivier Hainque <hain...@adacore.com>
Date: Tue Sep 10 16:46:02 2024 +0000
ada: Rework the Android sigtramp implementation
The initial signal handling code introduced for aarch64-android
overlooked details of the tasking runtime, not in the initial testing
perimeter.
Specifically, a reference to __gnat_sigtramp from __gnat_error_handler,
initially introduced for the arm port, was prevented if !arm on the
grounds that other ports would rely on kernel CFI. aarch64-android
does provide kernel CFI and __gnat_sigtramp was not provided for this
configuration.
But there is a similar reference from s-intman__android, which kicks in
as soon as the tasking runtime gets activated, triggering link failures.
Testing for more precise target specific parameters from Ada
code is inconvenient and replicating the logic is not attractive in
any case, so this change addresses the problem in the following
fashion:
- Always provide a __gnat_sigtramp entry point, common to the
tasking and non-tasking signal handling code for all the Android
configurations,
- There (C code), from target definition macros, select a path
that either routes directly to the actual signal handler or goes
through the intermediate layer providing hand crafted CFI
information which allows unwinding up to the interrupted code.
- Similarily to what was done for VxWorks, move the arm specific
definitions to a separate header file to make the general structure
of the common C code easier to grasp,
- Adjust the comments in the common sigtramp.h header to
account for such an organisation possibility.
gcc/ada/ChangeLog:
* sigtramp-armdroid.c: Refactor into ...
* sigtramp-android.c, sigtramp-android-asm.h: New files.
* Makefile.rtl (arm/aarch64-android section): Add
sigtramp-android.o to EXTRA_LIBGNAT_OBJS unconditionally. Add
sigtramp.h and sigtramp-android-asm.h to EXTRA_LIBGNAT_SRCS.
* init.c (android section, __gnat_error_handler): Defer to
__gnat_sigramp unconditionally again.
* sigtramp.h: Adjust comments to allow neutral signal handling
relays, merely forwarding to the underlying handler without any
intermediate CFI magic.
Diff:
---
gcc/ada/Makefile.rtl | 12 ++--
gcc/ada/init.c | 7 --
...{sigtramp-armdroid.c => sigtramp-android-asm.h} | 83 +++++-----------------
gcc/ada/sigtramp-android.c | 79 ++++++++++++++++++++
gcc/ada/sigtramp.h | 21 ++++--
5 files changed, 115 insertions(+), 87 deletions(-)
diff --git a/gcc/ada/Makefile.rtl b/gcc/ada/Makefile.rtl
index 3f27fe9aca90..246c0059fb7f 100644
--- a/gcc/ada/Makefile.rtl
+++ b/gcc/ada/Makefile.rtl
@@ -1430,22 +1430,20 @@ ifeq ($(strip $(filter-out arm% aarch64
linux-android%,$(target_cpu) $(target_os
EXTRA_GNATRTL_TASKING_OBJS=s-linux.o
- # 32bit arm relies on a sigtramp for signal->exception propagation
- # while aarch64 relies on kernel dwarf CFI. And as a 64bit target,
- # aarch64 can also incorporate support for 128bit arithmetic.
+ # ARM and aarch64 rely on different unwinding mechanisms, and as
+ # a 64bit target, aarch64 can also incorporate support for 128bit
+ # arithmetic.
ifeq ($(strip $(filter-out arm%, $(target_cpu))),)
SELECTED_PAIRS=arm-android
EH_MECHANISM=-arm
- SIGTRAMP_OBJ=sigtramp-armdroid.o
LIBGNAT_TARGET_PAIRS += \
s-linux.ads<libgnarl/s-linux__android-arm.ads
else
SELECTED_PAIRS=aarch64-android
EH_MECHANISM=-gcc
- SIGTRAMP_OBJ=
LIBGNAT_TARGET_PAIRS += \
s-linux.ads<libgnarl/s-linux__android-aarch64.ads
@@ -1453,8 +1451,8 @@ ifeq ($(strip $(filter-out arm% aarch64
linux-android%,$(target_cpu) $(target_os
EXTRA_GNATRTL_NONTASKING_OBJS = $(GNATRTL_128BIT_OBJS)
endif
- EXTRA_LIBGNAT_OBJS+=$(SIGTRAMP_OBJ)
- EXTRA_LIBGNAT_SRCS+=sigtramp.h
+ EXTRA_LIBGNAT_OBJS+=sigtramp-android.o
+ EXTRA_LIBGNAT_SRCS+=sigtramp.h sigtramp-android-asm.h
THREADSLIB =
GNATLIB_SHARED = gnatlib-shared-dual
LIBRARY_VERSION := $(LIB_VERSION)
diff --git a/gcc/ada/init.c b/gcc/ada/init.c
index ad51e2e054da..8019c09f80e0 100644
--- a/gcc/ada/init.c
+++ b/gcc/ada/init.c
@@ -2831,15 +2831,8 @@ static void
__gnat_error_handler (int sig, siginfo_t *si, void *ucontext)
{
__gnat_adjust_context_for_raise (sig, ucontext);
-
- /* The ARM port relies on a sigtramp. Others such as aarch64,
- dwarf info based, rely on kernel CFI. */
-#if defined(__arm__)
__gnat_sigtramp (sig, (void *) si, (void *) ucontext,
(__sigtramphandler_t *)&__gnat_map_signal);
-#else
- __gnat_map_signal (sig, si, ucontext);
-#endif
}
/* This must be in keeping with System.OS_Interface.Alternate_Stack_Size. */
diff --git a/gcc/ada/sigtramp-armdroid.c b/gcc/ada/sigtramp-android-asm.h
similarity index 60%
rename from gcc/ada/sigtramp-armdroid.c
rename to gcc/ada/sigtramp-android-asm.h
index c8b2a0aca8ac..72cebae1b546 100644
--- a/gcc/ada/sigtramp-armdroid.c
+++ b/gcc/ada/sigtramp-android-asm.h
@@ -2,11 +2,11 @@
* *
* GNAT COMPILER COMPONENTS *
* *
- * S I G T R A M P *
+ * S I G T R A M P - T A R G E T *
* *
- * Asm Implementation File *
+ * Asm Implementation Include File *
* *
- * Copyright (C) 2015-2024, Free Software Foundation, Inc. *
+ * Copyright (C) 2024, Free Software Foundation, Inc. *
* *
* GNAT is free software; you can redistribute it and/or modify it under *
* terms of the GNU General Public License as published by the Free Soft- *
@@ -29,62 +29,19 @@
* *
****************************************************************************/
-/******************************************************
- * ARM-Android version of the __gnat_sigtramp service *
- ******************************************************/
+/*****************************************************************
+ * CPU specific parts of the __gnat_sigtramp service for Android *
+ *****************************************************************/
-#include <sys/ucontext.h>
+/* The intended use mode of this header is to provide macros
+ and a prologue to the generation of an asm function, as in
-#include "sigtramp.h"
-/* See sigtramp.h for a general explanation of functionality. */
+ #include <this-header>
+ asm (SIGTRAMP_START(<symbol-name>));
+ asm (SIGTRAMP_BODY);
+ asm (SIGTRAMP_END(<symbol-name>));
-/* ----------------------
- -- General comments --
- ----------------------
-
- Stubs are generated from toplevel asms,
- The general idea is to establish CFA as the sigcontext
- and state where to find the registers as offsets from there.
-
- We support stubs for VxWorks and Android, providing unwind info for
- common registers. We might need variants with support for floating
- point or altivec registers as well at some point.
-
- For Android it would be simpler to write this in Asm since there's only
- one variant, but to keep it looking like the VxWorks stubs,
- C is the choice for our toplevel interface.
-
- Note that the registers we "restore" here are those to which we have
- direct access through the system sigcontext structure, which includes
- only a partial set of the non-volatiles ABI-wise. */
-
-/* -----------------------------------------
- -- Protypes for our internal asm stubs --
- -----------------------------------------
-
- The registers are expected to be at SIGCONTEXT + 12 (reference the
- sicontext structure in asm/sigcontext.h which describes the first
- 3 * 4byte fields.) Even though our symbols will remain local, the
- prototype claims "extern" and not "static" to prevent compiler complaints
- about a symbol used but never defined. */
-
-/* sigtramp stub providing unwind info for common registers. */
-
-extern void __gnat_sigtramp_common
- (int signo, void *siginfo, void *sigcontext,
- __sigtramphandler_t * handler);
-
-void __gnat_sigtramp (int signo, void *si, void *sc,
- __sigtramphandler_t * handler)
- __attribute__((optimize(2)));
-
-void __gnat_sigtramp (int signo, void *si, void *ucontext,
- __sigtramphandler_t * handler)
-{
- struct sigcontext *mcontext = &((ucontext_t *) ucontext)->uc_mcontext;
-
- __gnat_sigtramp_common (signo, si, mcontext, handler);
-}
+ and nothing else after. */
/* asm string construction helpers. */
@@ -103,6 +60,8 @@ void __gnat_sigtramp (int signo, void *si, void *ucontext,
#undef TCR
#define TCR(S) TAB(CR(S))
+#if defined(__arm__)
+
/* Trampoline body block
--------------------- */
@@ -145,19 +104,9 @@ TCR(".fnstart")
CR(".fnend") \
TCR(".size " S(SYM) ", .-" S(SYM))
-/*----------------------------
- -- And now, the real code --
- ---------------------------- */
+#endif
/* Text section start. The compiler isn't aware of that switch. */
asm (".text\n"
TCR(".align 2"));
-
-/* sigtramp stub for common registers. */
-
-#define TRAMP_COMMON __gnat_sigtramp_common
-
-asm (SIGTRAMP_START(TRAMP_COMMON));
-asm (SIGTRAMP_BODY);
-asm (SIGTRAMP_END(TRAMP_COMMON));
diff --git a/gcc/ada/sigtramp-android.c b/gcc/ada/sigtramp-android.c
new file mode 100644
index 000000000000..2fd42ba6f620
--- /dev/null
+++ b/gcc/ada/sigtramp-android.c
@@ -0,0 +1,79 @@
+/****************************************************************************
+ * *
+ * GNAT COMPILER COMPONENTS *
+ * *
+ * S I G T R A M P *
+ * *
+ * C/Asm Implementation File *
+ * *
+ * Copyright (C) 2015-2024, Free Software Foundation, Inc. *
+ * *
+ * GNAT is free software; you can redistribute it and/or modify it under *
+ * terms of the GNU General Public License as published by the Free Soft- *
+ * ware Foundation; either version 3, or (at your option) any later ver- *
+ * sion. GNAT is distributed in the hope that it will be useful, but WITH- *
+ * OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY *
+ * or FITNESS FOR A PARTICULAR PURPOSE. *
+ * *
+ * As a special exception under Section 7 of GPL version 3, you are granted *
+ * additional permissions described in the GCC Runtime Library Exception, *
+ * version 3.1, as published by the Free Software Foundation. *
+ * *
+ * In particular, you can freely distribute your programs built with the *
+ * GNAT Pro compiler, including any required library run-time units, using *
+ * any licensing terms of your choosing. See the AdaCore Software License *
+ * for full details. *
+ * *
+ * GNAT was originally developed by the GNAT team at New York University. *
+ * Extensive contributions were provided by Ada Core Technologies Inc. *
+ * *
+ ****************************************************************************/
+
+/**************************************************
+ * Android version of the __gnat_sigtramp service *
+ **************************************************/
+
+#include "sigtramp.h"
+
+/* The ARM port relies on CFI info setup here. Others such as aarch64
+ rely on kernel CFI and may relay to the handler directly. */
+
+#if defined(__arm__)
+#define __SETUP_CFI 1
+#else
+#define __SETUP_CFI 0
+#endif
+
+#if __SETUP_CFI
+
+/* Craft a sigtramp stub providing unwind info for common registers. */
+
+#define TRAMP_COMMON __gnat_sigtramp_common
+extern void TRAMP_COMMON
+ (int signo, void *siginfo, void *sigcontext,
+ __sigtramphandler_t * handler);
+
+#include <sys/ucontext.h>
+
+void __gnat_sigtramp (int signo, void *si, void *ucontext,
+ __sigtramphandler_t * handler)
+{
+ struct sigcontext *mcontext = &((ucontext_t *) ucontext)->uc_mcontext;
+ TRAMP_COMMON (signo, si, mcontext, handler);
+}
+
+#include <sigtramp-android-asm.h>
+
+asm (SIGTRAMP_START(TRAMP_COMMON));
+asm (SIGTRAMP_BODY);
+asm (SIGTRAMP_END(TRAMP_COMMON));
+
+#else /* !__SETUP_CFI */
+
+void __gnat_sigtramp (int signo, void *si, void *ucontext,
+ __sigtramphandler_t * handler)
+{
+ handler (signo, si, ucontext);
+}
+
+#endif
diff --git a/gcc/ada/sigtramp.h b/gcc/ada/sigtramp.h
index f99bc201b0d7..3c28c8aa56c9 100644
--- a/gcc/ada/sigtramp.h
+++ b/gcc/ada/sigtramp.h
@@ -29,11 +29,19 @@
* *
****************************************************************************/
-/* On targets where this is implemented, we resort to a signal trampoline to
- set up the DWARF Call Frame Information that lets unwinders walk through
- the signal frame up into the interrupted user code. This file introduces
- the relevant declarations. It should only be #included on targets that do
- implement the signal trampoline. */
+/* On targets where this is useful, a signal handler trampoline is setup to
+ allow interposing handcrafted DWARF Call Frame Information that lets
+ unwinders walk through a signal frame up into the interrupted user code.
+ This file introduces the relevant declarations.
+
+ For an OS family, in specific CPU configurations where kernel signal CFI
+ is known to be available, the trampoline may directly call the intended
+ handler without any intermediate CFI magic.
+
+ sigtramp*.c offers a convenient spot for picking such alternatives, as
+ it allows testing for precise target predicates and is easily shared
+ by the tasking and non-tasking runtimes for a given OS (e.g. s-intman.adb
+ and init.c:__gnat_error_handler). */
#ifdef __cplusplus
extern "C" {
@@ -54,7 +62,8 @@ extern void __gnat_sigtramp (int signo, void *siginfo, void
*sigcontext,
__sigtramphandler_t * handler);
/* The signal trampoline is to be called from an established signal handler.
- It sets up the DWARF CFI and calls HANDLER (SIGNO, SIGINFO, SIGCONTEXT).
+ It calls HANDLER (SIGNO, SIGINFO, SIGCONTEXT) after setting up the DWARF
+ CFI if needed.
The trampoline construct makes it so that the unwinder jumps over it + the
signal handler + the kernel frame. For a typical backtrace from the raise
