[PATCH v3 5/6] stack: Fix stack unwind failure on mips

[PATCH v3 5/6] stack: Fix stack unwind failure on mips

[Ying Huang]

From: Ying Huang <ying.huang@oss.cipunited.com>

Add abi_cfi, set_initial_registers_tid, unwind on mips.

Signed-off-by: Ying Huang <ying.huang@oss.cipunited.com>
---
 backends/Makefile.am    |  3 +-
 backends/mips_cfi.c     | 68 +++++++++++++++++++++++++++++++++
 backends/mips_init.c    |  4 ++
 backends/mips_initreg.c | 61 ++++++++++++++++++++++++++++++
 backends/mips_unwind.c  | 84 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 219 insertions(+), 1 deletion(-)
 create mode 100644 backends/mips_cfi.c
 create mode 100644 backends/mips_initreg.c
 create mode 100644 backends/mips_unwind.c

diff --git a/backends/Makefile.am b/backends/Makefile.am
index ad95526e..5e7b7f21 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -102,7 +102,8 @@ loongarch_SRCS = loongarch_init.c loongarch_symbol.c loongarch_cfi.c \
 
 arc_SRCS = arc_init.c arc_symbol.c
 
-mips_SRCS = mips_init.c mips_symbol.c mips_attrs.c
+mips_SRCS = mips_init.c mips_symbol.c mips_attrs.c mips_initreg.c \
+	    mips_cfi.c mips_unwind.c
 
 libebl_backends_a_SOURCES = $(i386_SRCS) $(sh_SRCS) $(x86_64_SRCS) \
 			    $(ia64_SRCS) $(alpha_SRCS) $(arm_SRCS) \
diff --git a/backends/mips_cfi.c b/backends/mips_cfi.c
new file mode 100644
index 00000000..60cf8111
--- /dev/null
+++ b/backends/mips_cfi.c
@@ -0,0 +1,68 @@
+/* MIPS ABI-specified defaults for DWARF CFI.
+   Copyright (C) 2009 Red Hat, Inc.
+   Copyright (C) 2024 CIP United Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <dwarf.h>
+
+#define BACKEND mips_
+#include "libebl_CPU.h"
+
+int
+mips_abi_cfi (Ebl *ebl __attribute__ ((unused)), Dwarf_CIE *abi_info)
+{
+  static const uint8_t abi_cfi[] =
+    {
+      DW_CFA_def_cfa, ULEB128_7 (31), ULEB128_7 (0),
+      /* Callee-saved regs.  */
+      DW_CFA_same_value, ULEB128_7 (16), /* s0 */
+      DW_CFA_same_value, ULEB128_7 (17), /* s1 */
+      DW_CFA_same_value, ULEB128_7 (18), /* s2 */
+      DW_CFA_same_value, ULEB128_7 (19), /* s3 */
+      DW_CFA_same_value, ULEB128_7 (20), /* s4 */
+      DW_CFA_same_value, ULEB128_7 (21), /* s5 */
+      DW_CFA_same_value, ULEB128_7 (22), /* s6 */
+      DW_CFA_same_value, ULEB128_7 (23), /* s7 */
+      DW_CFA_same_value, ULEB128_7 (28), /* gp */
+      DW_CFA_same_value, ULEB128_7 (29), /* sp */
+      DW_CFA_same_value, ULEB128_7 (30), /* fp */
+
+      DW_CFA_val_offset, ULEB128_7 (29), ULEB128_7 (0),
+    };
+
+  abi_info->initial_instructions = abi_cfi;
+  abi_info->initial_instructions_end = &abi_cfi[sizeof abi_cfi];
+  abi_info->data_alignment_factor = 8;
+
+  abi_info->return_address_register = 31; /* %ra */
+
+  return 0;
+}
diff --git a/backends/mips_init.c b/backends/mips_init.c
index 521e6e51..1a2456b1 100644
--- a/backends/mips_init.c
+++ b/backends/mips_init.c
@@ -58,5 +58,9 @@ mips_init (Elf *elf __attribute__ ((unused)),
   HOOK (eh, check_object_attribute);
   HOOK (eh, check_special_symbol);
   HOOK (eh, check_reloc_target_type);
+  HOOK (eh, set_initial_registers_tid);
+  HOOK (eh, abi_cfi);
+  HOOK (eh, unwind);
+  eh->frame_nregs = 71;
   return eh;
 }
diff --git a/backends/mips_initreg.c b/backends/mips_initreg.c
new file mode 100644
index 00000000..21e7dedb
--- /dev/null
+++ b/backends/mips_initreg.c
@@ -0,0 +1,61 @@
+/* Fetch live process registers from TID.
+   Copyright (C) 2024 CIP United Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <stdlib.h>
+#if (defined(mips) || defined(__mips) || defined(__mips__) || defined(MIPS) || defined(__MIPS__)) && defined(__linux__)
+# include <sys/user.h>
+# include <sys/ptrace.h>
+#include <asm/ptrace.h>
+#endif
+
+#define BACKEND mips_
+#include "libebl_CPU.h"
+
+
+bool
+mips_set_initial_registers_tid (pid_t tid __attribute__ ((unused)),
+			  ebl_tid_registers_t *setfunc __attribute__ ((unused)),
+				  void *arg __attribute__ ((unused)))
+{
+#if (!defined(mips) && !defined(__mips) && !defined(__mips__) && !defined(MIPS) && !defined(__MIPS__)) || !defined(__linux__)
+  return false;
+#else /* __mips__ */
+/* For PTRACE_GETREGS */
+
+  struct pt_regs gregs;
+  if (ptrace (PTRACE_GETREGS, tid, 0, &gregs) != 0)
+    return false;
+  if (! setfunc (-1, 1, (Dwarf_Word *) &gregs.cp0_epc, arg))
+    return false;
+  return setfunc (0, 32, (Dwarf_Word *) &gregs.regs[0], arg);
+#endif /* __mips__ */
+}
diff --git a/backends/mips_unwind.c b/backends/mips_unwind.c
new file mode 100644
index 00000000..9acf87a7
--- /dev/null
+++ b/backends/mips_unwind.c
@@ -0,0 +1,84 @@
+/* Get previous frame state for an existing frame state.
+   Copyright (C) 2016 The Qt Company Ltd.
+   Copyright (C) 2024 CIP United Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#define BACKEND mips_
+#define SP_REG 29
+#define FP_REG 30
+#define LR_REG 31
+#define FP_OFFSET 0
+#define LR_OFFSET 8
+#define SP_OFFSET 16
+
+#include "libebl_CPU.h"
+
+/* There was no CFI. Maybe we happen to have a frame pointer and can unwind from that?  */
+
+bool
+EBLHOOK(unwind) (Ebl *ebl __attribute__ ((unused)), Dwarf_Addr pc __attribute__ ((unused)),
+		 ebl_tid_registers_t *setfunc, ebl_tid_registers_get_t *getfunc,
+		 ebl_pid_memory_read_t *readfunc, void *arg,
+		 bool *signal_framep __attribute__ ((unused)))
+{
+  Dwarf_Word fp, lr, sp;
+
+  if (!getfunc(LR_REG, 1, &lr, arg))
+    return false;
+
+  if (lr == 0 || !setfunc(-1, 1, &lr, arg))
+    return false;
+
+  if (!getfunc(FP_REG, 1, &fp, arg))
+    fp = 0;
+
+  if (!getfunc(SP_REG, 1, &sp, arg))
+    sp = 0;
+
+  Dwarf_Word newLr, newFp, newSp;
+
+  if (!readfunc(fp + LR_OFFSET, &newLr, arg))
+    newLr = 0;
+
+  if (!readfunc(fp + FP_OFFSET, &newFp, arg))
+    newFp = 0;
+
+  newSp = fp + SP_OFFSET;
+
+  // These are not fatal if they don't work. They will just prevent unwinding at the next frame.
+  setfunc(LR_REG, 1, &newLr, arg);
+  setfunc(FP_REG, 1, &newFp, arg);
+  setfunc(SP_REG, 1, &newSp, arg);
+
+  // If the fp is invalid, we might still have a valid lr.
+  // But if the fp is valid, then the stack should be moving in the right direction.
+  return fp == 0 || newSp > sp;
+}
-- 
2.39.2

Re: [PATCH v3 5/6] stack: Fix stack unwind failure on mips

[Mark Wielaard]

Hi Ying,

On Tue, Mar 05, 2024 at 05:51:21PM +0800, Ying Huang wrote:
> From: Ying Huang <ying.huang@oss.cipunited.com>
> 
> Add abi_cfi, set_initial_registers_tid, unwind on mips.

Sorry for reviewing out of order. But this one looked easy enough.
The new abi_cfi, unwind and set_initial_registers_tid implementations
looks correct (even though I don't really known MIPS).

Pushed with the following ChangeLog entry added to the commit message.

        * backends/Makefile.am (mips_SRCS): Add mips_initreg.c,
        mips_cfi.c and mips_unwind.c.
        * backends/mips_init.c (mips_init): HOOK abi_cfi, unwind and
        set_initial_registers_tid. Set frame_nregs to 71.
        * backends/mips_cfi.c: New file.
        * backends/mips_initreg.c: Likewise.
        * backends/mips_unwind.c: Likewise.

It would be helpful to see if you could come up with a testcase
similar to the ones in tests/run-backtrace-core-<arch>.sh with
tests/tests/backtrace.<arch>.{exec,core}.bz2 so it can be tested from
a non-MIPS setup (as opposed to the tests/run-backtrace-native.sh and
tests/run-backtrace-native-core.sh tests).

Thanks,

Mark

Re: [PATCH v3 5/6] stack: Fix stack unwind failure on mips

[Ying Huang]

Hi Mark,

> It would be helpful to see if you could come up with a testcase
> similar to the ones in tests/run-backtrace-core-<arch>.sh with
> tests/tests/backtrace.<arch>.{exec,core}.bz2 so it can be tested from
> a non-MIPS setup (as opposed to the tests/run-backtrace-native.sh and
> tests/run-backtrace-native-core.sh tests).
>
> Thanks,
>
> Mark

I am glad to add a testcase and could you help review other patches?

Thanks,

Ying