Add custom getcontext() implementation for Android.

This adds a minimalistic implementation of getcontext()
for Android/ARM and Android/x86. The provided code is
in assembly and only implements the bare minimum required
by Breakpad to get the current processor state.

Note that:

- The FPU state is not saved to the ucontext_t on ARM.
  (that's actually the main difference with a normal
   getcontext() implementation).

  This is normal. On Linux/ARM, such state must be
  obtained with PTRACE_GETVFPREGS instead. This will
  be implemented in a future patch.

- On x86, only the 'regular' FPU state is saved, to
  mimic the GLibc/i386 implementation. The state of
  SSE/SSE2/etc registers is not part of the upstream
  getcontext() implementation.
Review URL: https://breakpad.appspot.com/444002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1024 4c0a9323-5329-0410-9bdc-e9ce6186880e

6 files changed, 342 insertions, 15 deletions

diff --git a/src/client/linux/handler/exception_handler.cc b/src/client/linux/handler/exception_handler.cc
index 4a5932c1..27ac1544 100644
--- a/src/client/linux/handler/exception_handler.cc
+++ b/src/client/linux/handler/exception_handler.cc
@@ -324,16 +324,11 @@ bool ExceptionHandler::HandleSignal(int sig, siginfo_t* info, void* uc) {
 // This is a public interface to HandleSignal that allows the client to
 // generate a crash dump. This function may run in a compromised context.
 bool ExceptionHandler::SimulateSignalDelivery(int sig) {
-#ifdef __ANDROID__
-  // Android doesn't provide getcontext().
-  return false;
-#else
   siginfo_t siginfo;
   my_memset(&siginfo, 0, sizeof(siginfo_t));
   struct ucontext context;
   getcontext(&context);
   return HandleSignal(sig, &siginfo, &context);
-#endif
 }
 
 // This function may run in a compromised context: see the top of the file.
@@ -457,7 +452,6 @@ bool ExceptionHandler::WriteMinidump(const string& dump_path,
 }
 
 bool ExceptionHandler::WriteMinidump() {
-#if !defined(__ARM_EABI__) && !defined(__ANDROID__)
   if (!IsOutOfProcess() && !minidump_descriptor_.IsFD()) {
     // Update the path of the minidump so that this can be called multiple times
     // and new files are created for each minidump.  This is done before the
@@ -478,14 +472,14 @@ bool ExceptionHandler::WriteMinidump() {
   int getcontext_result = getcontext(&context.context);
   if (getcontext_result)
     return false;
+#if !defined(__ARM_EABI__)
+  // FPU state is not part of ARM EABI ucontext_t.
   memcpy(&context.float_state, context.context.uc_mcontext.fpregs,
          sizeof(context.float_state));
+#endif
   context.tid = sys_gettid();
 
   return GenerateDump(&context);
-#else
-  return false;
-#endif  // !defined(__ARM_EABI__) && !defined(__ANDROID__)
 }
 
 void ExceptionHandler::AddMappingInfo(const string& name,
diff --git a/src/common/android/breakpad_getcontext.S b/src/common/android/breakpad_getcontext.S
new file mode 100644
index 00000000..13ccd46b
--- /dev/null
+++ b/src/common/android/breakpad_getcontext.S
@@ -0,0 +1,145 @@
+// Copyright (c) 2012, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// A minimalistic implementation of getcontext() to be used by
+// Google Breakpad on Android.
+
+#include "common/android/ucontext_constants.h"
+
+/* int getcontext (ucontext_t *ucp) */
+
+#ifdef __arm__
+
+  .text
+  .global breakpad_getcontext
+  .hidden breakpad_getcontext
+  .type breakpad_getcontext, #function
+  .align 0
+  .fnstart
+breakpad_getcontext:
+
+  /* First, save r4-r11 */
+  add   r1, r0, #(MCONTEXT_GREGS_OFFSET + 4*4)
+  stm   r1, {r4-r11}
+
+  /* r12 is a scratch register, don't save it */
+
+  /* Save sp and lr explicitely. */
+  /* - sp can't be stored with stmia in Thumb-2 */
+  /* - STM instructions that store sp and pc are deprecated in ARM */
+  str   sp, [r0, #(MCONTEXT_GREGS_OFFSET + 13*4)]
+  str   lr, [r0, #(MCONTEXT_GREGS_OFFSET + 14*4)]
+
+  /* Save the caller's address in 'pc' */
+  str   lr, [r0, #(MCONTEXT_GREGS_OFFSET + 15*4)]
+
+  /* Save ucontext_t* pointer accross next call */
+  mov   r4, r0
+
+  /* Call sigprocmask(SIG_BLOCK, NULL, &(ucontext->uc_sigmask)) */
+  mov   r0, #0  /* SIG_BLOCK */
+  mov   r1, #0  /* NULL */
+  add   r2, r4, #UCONTEXT_SIGMASK_OFFSET
+  bl    sigprocmask(PLT)
+
+  /* Intentionally do not save the FPU state here. This is because on
+   * Linux/ARM, one should instead use ptrace(PTRACE_GETFPREGS) or
+   * ptrace(PTRACE_GETVFPREGS) to get it.
+   *
+   * Note that a real implementation of getcontext() would need to save
+   * this here to allow setcontext()/swapcontext() to work correctly.
+   */
+
+  /* Restore the values of r4 and lr */
+  mov   r0, r4
+  ldr   lr, [r0, #(MCONTEXT_GREGS_OFFSET + 14*4)]
+  ldr   r4, [r0, #(MCONTEXT_GREGS_OFFSET +  4*4)]
+
+  /* Return 0 */
+  mov   r0, #0
+  bx    lr
+
+  .fnend
+  .size breakpad_getcontext, . - breakpad_getcontext
+
+#elif defined(__i386__)
+
+  .text
+  .global breakpad_getcontext
+  .hidden breakpad_getcontext
+  .align 4
+  .type breakpad_getcontext, @function
+
+breakpad_getcontext:
+
+  movl 4(%esp), %eax   /* eax = uc */
+
+  /* Save register values */
+  movl %ecx, MCONTEXT_ECX_OFFSET(%eax)
+  movl %edx, MCONTEXT_EDX_OFFSET(%eax)
+  movl %ebx, MCONTEXT_EBX_OFFSET(%eax)
+  movl %edi, MCONTEXT_EDI_OFFSET(%eax)
+  movl %esi, MCONTEXT_ESI_OFFSET(%eax)
+  movl %ebp, MCONTEXT_EBP_OFFSET(%eax)
+
+  movl (%esp), %edx   /* return address */
+  lea  4(%esp), %ecx  /* exclude return address from stack */
+  mov  %edx, MCONTEXT_EIP_OFFSET(%eax)
+  mov  %ecx, MCONTEXT_ESP_OFFSET(%eax)
+
+  xorl %ecx, %ecx
+  movw %fs, %cx
+  mov  %ecx, MCONTEXT_FS_OFFSET(%eax)
+
+  movl $0, MCONTEXT_EAX_OFFSET(%eax)
+
+  /* Save floating point state to fpregstate, then update
+   * the fpregs pointer to point to it */
+  leal UCONTEXT_FPREGS_MEM_OFFSET(%eax), %ecx
+  fnstenv (%ecx)
+  fldenv  (%ecx)
+  mov %ecx, UCONTEXT_FPREGS_OFFSET(%eax)
+
+  /* Save signal mask: sigprocmask(SIGBLOCK, NULL, &uc->uc_sigmask) */
+  leal UCONTEXT_SIGMASK_OFFSET(%eax), %edx
+  xorl %ecx, %ecx
+  push %edx   /* &uc->uc_sigmask */
+  push %ecx   /* NULL */
+  push %ecx   /* SIGBLOCK == 0 on i386 */
+  call sigprocmask@PLT
+  addl $12, %esp
+
+  movl $0, %eax
+  ret
+
+  .size breakpad_getcontext, . - breakpad_getcontext
+
+#else
+#error "This file has not been ported for your CPU!"
+#endif
diff --git a/src/common/android/breakpad_getcontext_unittest.cc b/src/common/android/breakpad_getcontext_unittest.cc
new file mode 100644
index 00000000..004390c3
--- /dev/null
+++ b/src/common/android/breakpad_getcontext_unittest.cc
@@ -0,0 +1,76 @@
+// Copyright (c) 2012, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <sys/ucontext.h>
+
+#include "breakpad_googletest_includes.h"
+#include "common/android/ucontext_constants.h"
+
+TEST(AndroidUContext, GRegsOffset) {
+#ifdef __arm__
+  // There is no gregs[] array on ARM, so compare to the offset of
+  // first register fields, since they're stored in order.
+  ASSERT_EQ(MCONTEXT_GREGS_OFFSET, offsetof(ucontext_t,uc_mcontext.arm_r0));
+#elif defined(__i386__)
+  ASSERT_EQ(MCONTEXT_GREGS_OFFSET, offsetof(ucontext_t,uc_mcontext.gregs));
+#define CHECK_REG(x) \
+  ASSERT_EQ(MCONTEXT_##x##_OFFSET, \
+            offsetof(ucontext_t,uc_mcontext.gregs[REG_##x]))
+  CHECK_REG(GS);
+  CHECK_REG(FS);
+  CHECK_REG(ES);
+  CHECK_REG(DS);
+  CHECK_REG(EDI);
+  CHECK_REG(ESI);
+  CHECK_REG(EBP);
+  CHECK_REG(ESP);
+  CHECK_REG(EBX);
+  CHECK_REG(EDX);
+  CHECK_REG(ECX);
+  CHECK_REG(EAX);
+  CHECK_REG(TRAPNO);
+  CHECK_REG(ERR);
+  CHECK_REG(EIP);
+  CHECK_REG(CS);
+  CHECK_REG(EFL);
+  CHECK_REG(UESP);
+  CHECK_REG(SS);
+
+  ASSERT_EQ(UCONTEXT_FPREGS_OFFSET, offsetof(ucontext_t,uc_mcontext.fpregs));
+
+  ASSERT_EQ(UCONTEXT_FPREGS_MEM_OFFSET,
+            offsetof(ucontext_t,__fpregs_mem));
+#else
+  ASSERT_EQ(MCONTEXT_GREGS_OFFSET, offsetof(ucontext_t,uc_mcontext.gregs));
+#endif
+}
+
+TEST(AndroidUContext, SigmakOffset) {
+  ASSERT_EQ(UCONTEXT_SIGMASK_OFFSET, offsetof(ucontext_t,uc_sigmask));
+}
diff --git a/src/common/android/include/sys/ucontext.h b/src/common/android/include/sys/ucontext.h
index 7f0eb5a3..4a4e77c1 100644
--- a/src/common/android/include/sys/ucontext.h
+++ b/src/common/android/include/sys/ucontext.h
@@ -50,11 +50,15 @@ extern "C" {
 #include <asm/sigcontext.h>
 typedef struct sigcontext mcontext_t;
 
+// The ARM kernel uses a 64-bit signal mask.
+typedef uint32_t  kernel_sigmask_t[2];
+
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
+  kernel_sigmask_t uc_sigmask;
   // Other fields are not used by Google Breakpad. Don't define them.
 } ucontext_t;
 
@@ -110,12 +114,16 @@ enum {
   REG_SS,
 };
 
+// The i386 kernel uses a 64-bit signal mask.
+typedef uint32_t kernel_sigmask_t[2];
+
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  // Other fields are not used by Google Breakpad. Don't define them.
+  kernel_sigmask_t uc_sigmask;
+  struct _libc_fpstate __fpregs_mem;
 } ucontext_t;
 
 #elif defined(__mips__)
@@ -142,11 +150,15 @@ typedef struct {
   uint32_t lo3;
 } mcontext_t;
 
+// The MIPS kernel uses a 128-bit signal mask.
+typedef uint32_t kernel_sigmask_t[4];
+
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
+  kernel_sigmask_t uc_sigmask;
   // Other fields are not used by Google Breakpad. Don't define them.
 } ucontext_t;
 
diff --git a/src/common/android/include/ucontext.h b/src/common/android/include/ucontext.h
index 6608e063..29db8ade 100644
--- a/src/common/android/include/ucontext.h
+++ b/src/common/android/include/ucontext.h
@@ -30,12 +30,27 @@
 #ifndef GOOGLE_BREAKPAD_COMMON_ANDROID_INCLUDE_UCONTEXT_H
 #define GOOGLE_BREAKPAD_COMMON_ANDROID_INCLUDE_UCONTEXT_H
 
+#include <sys/cdefs.h>
+
+#ifdef __BIONIC_UCONTEXT_H
+#include <ucontext.h>
+#else
+
 #include <sys/ucontext.h>
 
-// TODO: Provide a portable implementation of getcontext() then
-//        update ExceptionHandler::WriteMinidump() in
-//        src/client/linux/handler/exception_handler.cc to use it.
-//
-// extern int getcontext(ucontext_t* ucp);
+#ifdef __cplusplus
+extern "C" {
+#endif  // __cplusplus
+
+// Provided by src/android/common/breakpad_getcontext.S
+int breakpad_getcontext(ucontext_t* ucp);
+
+#define getcontext(x)   breakpad_getcontext(x)
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif  // __cplusplus
+
+#endif  // __BIONIC_UCONTEXT_H
 
 #endif  // GOOGLE_BREAKPAD_COMMON_ANDROID_INCLUDE_UCONTEXT_H
diff --git a/src/common/android/ucontext_constants.h b/src/common/android/ucontext_constants.h
new file mode 100644
index 00000000..9c7a6971
--- /dev/null
+++ b/src/common/android/ucontext_constants.h
@@ -0,0 +1,85 @@
+// Copyright (c) 2012, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This header can be included either from a C, C++ or Assembly file.
+// Its purpose is to contain constants that must match the offsets of
+// various fields in ucontext_t.
+//
+// They should match the definitions from
+// src/common/android/include/sys/ucontext.h
+//
+// Used by src/common/android/breakpad_getcontext.S
+// Tested by src/common/android/testing/breakpad_getcontext_unittest.cc
+
+#ifndef GOOGLEBREAKPAD_COMMON_ANDROID_UCONTEXT_CONSTANTS_H
+#define GOOGLEBREAKPAD_COMMON_ANDROID_UCONTEXT_CONSTANTS_H
+
+#if defined(__arm__)
+
+#define  MCONTEXT_GREGS_OFFSET     32
+#define  UCONTEXT_SIGMASK_OFFSET   104
+
+#elif defined(__i386__)
+
+#define  MCONTEXT_GREGS_OFFSET     20
+#define  MCONTEXT_GS_OFFSET        (MCONTEXT_GREGS_OFFSET + 0*4)
+#define  MCONTEXT_FS_OFFSET        (MCONTEXT_GREGS_OFFSET + 1*4)
+#define  MCONTEXT_ES_OFFSET        (MCONTEXT_GREGS_OFFSET + 2*4)
+#define  MCONTEXT_DS_OFFSET        (MCONTEXT_GREGS_OFFSET + 3*4)
+#define  MCONTEXT_EDI_OFFSET       (MCONTEXT_GREGS_OFFSET + 4*4)
+#define  MCONTEXT_ESI_OFFSET       (MCONTEXT_GREGS_OFFSET + 5*4)
+#define  MCONTEXT_EBP_OFFSET       (MCONTEXT_GREGS_OFFSET + 6*4)
+#define  MCONTEXT_ESP_OFFSET       (MCONTEXT_GREGS_OFFSET + 7*4)
+#define  MCONTEXT_EBX_OFFSET       (MCONTEXT_GREGS_OFFSET + 8*4)
+#define  MCONTEXT_EDX_OFFSET       (MCONTEXT_GREGS_OFFSET + 9*4)
+#define  MCONTEXT_ECX_OFFSET       (MCONTEXT_GREGS_OFFSET + 10*4)
+#define  MCONTEXT_EAX_OFFSET       (MCONTEXT_GREGS_OFFSET + 11*4)
+#define  MCONTEXT_TRAPNO_OFFSET    (MCONTEXT_GREGS_OFFSET + 12*4)
+#define  MCONTEXT_ERR_OFFSET       (MCONTEXT_GREGS_OFFSET + 13*4)
+#define  MCONTEXT_EIP_OFFSET       (MCONTEXT_GREGS_OFFSET + 14*4)
+#define  MCONTEXT_CS_OFFSET        (MCONTEXT_GREGS_OFFSET + 15*4)
+#define  MCONTEXT_EFL_OFFSET       (MCONTEXT_GREGS_OFFSET + 16*4)
+#define  MCONTEXT_UESP_OFFSET      (MCONTEXT_GREGS_OFFSET + 17*4)
+#define  MCONTEXT_SS_OFFSET        (MCONTEXT_GREGS_OFFSET + 18*4)
+
+#define  UCONTEXT_SIGMASK_OFFSET   108
+
+#define  UCONTEXT_FPREGS_OFFSET       96
+#define  UCONTEXT_FPREGS_MEM_OFFSET   116
+
+#elif defined(__mips__)
+
+#define  MCONTEXT_GREGS_OFFSET     0
+#define  UCONTEXT_SIGMASK_OFFSET   0
+
+#else
+#error "This header has not been ported for your CPU"
+#endif
+
+#endif  // GOOGLEBREAKPAD_COMMON_ANDROID_UCONTEXT_CONSTANTS_H