Stack-unwinding through signal frames on mips

Detect if current frame is a signal frame by checking for preceeding
syscall instruction. For signal frames, update the cursor correctly
from user context before calling dwarf_step.

src/mips/Gis_signal_frame.c

@@ -1,4 +1,5 @@
 /* libunwind - a platform-independent unwind library
+   Copyright (C) 2015 Imagination Technologies Limited
    Copyright (C) 2008 CodeSourcery
 
 This file is part of libunwind.
@@ -25,11 +26,53 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 #include "unwind_i.h"
 #include <stdio.h>
 
-/* FIXME for MIPS.  */
-
 PROTECTED int
 unw_is_signal_frame (unw_cursor_t *cursor)
 {
-  printf ("%s: implement me\n", __FUNCTION__);
+  struct cursor *c = (struct cursor *) cursor;
-  return -UNW_ENOINFO;
+  unw_word_t w0, w1, ip;
+  unw_addr_space_t as;
+  unw_accessors_t *a;
+  void *arg;
+  int ret;
+
+  as = c->dwarf.as;
+  a = unw_get_accessors (as);
+  arg = c->dwarf.as_arg;
+
+  ip = c->dwarf.ip;
+
+  /* syscall */
+  if ((ret = (*a->access_mem) (as, ip + 4, &w1, 0, arg)) < 0)
+    return 0;
+  if ((w1 & 0xffffffff) != 0x0c)
+    return 0;
+
+  /* li v0, 0x1061 (rt) or li v0, 0x1017 */
+  if ((ret = (*a->access_mem) (as, ip, &w0, 0, arg)) < 0)
+    return 0;
+
+  switch (c->dwarf.as->abi)
+    {
+    case UNW_MIPS_ABI_O32:
+      switch (w0 & 0xffffffff)
+        {
+        case 0x24021061:
+          return 1;
+        case 0x24021017:
+          return 2;
+        default:
+          return 0;
+        }
+    case UNW_MIPS_ABI_N64:
+      switch (w0 & 0xffffffff)
+        {
+        case 0x2402145b:
+          return 1;
+        default:
+          return 0;
+        }
+    default:
+      return 0;
+    }
 }

src/mips/Gstep.c

@@ -1,4 +1,5 @@
 /* libunwind - a platform-independent unwind library
+   Copyright (C) 2015 Imagination Technologies Limited
    Copyright (C) 2008 CodeSourcery
 
 This file is part of libunwind.
@@ -25,17 +26,100 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 #include "unwind_i.h"
 #include "offsets.h"
 
+PROTECTED int
+unw_handle_signal_frame (unw_cursor_t *cursor)
+{
+  struct cursor *c = (struct cursor *) cursor;
+  unw_word_t sc_addr, sp, sp_addr = c->dwarf.cfa;
+  unw_word_t ra, fp;
+  int ret;
+
+  switch (unw_is_signal_frame (cursor)) {
+  case 1:
+    sc_addr = sp_addr + LINUX_SF_TRAMP_SIZE + sizeof (siginfo_t) +
+              LINUX_UC_MCONTEXT_OFF;
+    break;
+  case 2:
+    sc_addr = sp_addr + LINUX_UC_MCONTEXT_OFF;
+    break;
+  default:
+    return -UNW_EUNSPEC;
+  }
+
+  if (tdep_big_endian(c->dwarf.as))
+    sc_addr += 4;
+
+  c->sigcontext_addr = sc_addr;
+
+  /* Update the dwarf cursor. */
+  c->dwarf.loc[UNW_MIPS_R0]  = DWARF_LOC (sc_addr + LINUX_SC_R0_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R1]  = DWARF_LOC (sc_addr + LINUX_SC_R1_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R2]  = DWARF_LOC (sc_addr + LINUX_SC_R2_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R3]  = DWARF_LOC (sc_addr + LINUX_SC_R3_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R4]  = DWARF_LOC (sc_addr + LINUX_SC_R4_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R5]  = DWARF_LOC (sc_addr + LINUX_SC_R5_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R6]  = DWARF_LOC (sc_addr + LINUX_SC_R6_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R7]  = DWARF_LOC (sc_addr + LINUX_SC_R7_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R8]  = DWARF_LOC (sc_addr + LINUX_SC_R8_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R9]  = DWARF_LOC (sc_addr + LINUX_SC_R9_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R10] = DWARF_LOC (sc_addr + LINUX_SC_R10_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R11] = DWARF_LOC (sc_addr + LINUX_SC_R11_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R12] = DWARF_LOC (sc_addr + LINUX_SC_R12_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R13] = DWARF_LOC (sc_addr + LINUX_SC_R13_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R14] = DWARF_LOC (sc_addr + LINUX_SC_R14_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R15] = DWARF_LOC (sc_addr + LINUX_SC_R15_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R16] = DWARF_LOC (sc_addr + LINUX_SC_R16_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R17] = DWARF_LOC (sc_addr + LINUX_SC_R17_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R18] = DWARF_LOC (sc_addr + LINUX_SC_R18_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R19] = DWARF_LOC (sc_addr + LINUX_SC_R19_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R20] = DWARF_LOC (sc_addr + LINUX_SC_R20_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R21] = DWARF_LOC (sc_addr + LINUX_SC_R21_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R22] = DWARF_LOC (sc_addr + LINUX_SC_R22_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R23] = DWARF_LOC (sc_addr + LINUX_SC_R23_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R24] = DWARF_LOC (sc_addr + LINUX_SC_R24_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R25] = DWARF_LOC (sc_addr + LINUX_SC_R25_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R26] = DWARF_LOC (sc_addr + LINUX_SC_R26_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R27] = DWARF_LOC (sc_addr + LINUX_SC_R27_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R28] = DWARF_LOC (sc_addr + LINUX_SC_R28_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R29] = DWARF_LOC (sc_addr + LINUX_SC_R29_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R30] = DWARF_LOC (sc_addr + LINUX_SC_R30_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_R31] = DWARF_LOC (sc_addr + LINUX_SC_R31_OFF, 0);
+  c->dwarf.loc[UNW_MIPS_PC] = DWARF_LOC (sc_addr + LINUX_SC_PC_OFF, 0);
+
+  /* Set SP/CFA and PC/IP. */
+  dwarf_get (&c->dwarf, c->dwarf.loc[UNW_MIPS_R29], &c->dwarf.cfa);
+
+  if ((ret = dwarf_get(&c->dwarf, DWARF_LOC(sc_addr + LINUX_SC_PC_OFF, 0),
+                       &c->dwarf.ip)) < 0)
+    return ret;
+
+  if ((ret = dwarf_get(&c->dwarf, DWARF_LOC(sc_addr + LINUX_SC_R31_OFF, 0),
+                       &ra)) < 0)
+    return ret;
+  if ((ret = dwarf_get(&c->dwarf, DWARF_LOC(sc_addr + LINUX_SC_R30_OFF, 0),
+                       &fp)) < 0)
+    return ret;
+
+  Debug (2, "SH (ip=0x%016llx, ra=0x%016llx, sp=0x%016llx, fp=0x%016llx)\n",
+         (unsigned long long)c->dwarf.ip, (unsigned long long)ra,
+         (unsigned long long)c->dwarf.cfa, (unsigned long long)fp);
+
+  c->dwarf.pi_valid = 0;
+  c->dwarf.use_prev_instr = 0;
+
+  return 1;
+}
+
 PROTECTED int
 unw_step (unw_cursor_t *cursor)
 {
   struct cursor *c = (struct cursor *) cursor;
   int ret;
 
-  Debug (1, "(cursor=%p)\n", c);
+  ret = unw_handle_signal_frame (cursor);
-
+  if (ret < 0)
-  /* Try DWARF-based unwinding...  this is the only method likely to work for
+    /* Not a signal frame, try DWARF-based unwinding. */
-     MIPS.  */
+    ret = dwarf_step (&c->dwarf);
-  ret = dwarf_step (&c->dwarf);
 
   if (unlikely (ret == -UNW_ESTOPUNWIND))
     return ret;

src/mips/offsets.h

@@ -9,6 +9,10 @@
 
 /* Offsets for MIPS Linux "ucontext_t":  */
 
+/* First 24 bytes in sigframe are argument save space and padding for
+what used to be signal trampolines. Ref: arch/mips/kernel/signal.c */
+#define LINUX_SF_TRAMP_SIZE 0x18
+
 #if _MIPS_SIM == _ABIO32
 
 # define LINUX_UC_FLAGS_OFF     0x0
@@ -39,4 +43,44 @@
 # define LINUX_UC_MCONTEXT_PC   0x268
 # define LINUX_UC_MCONTEXT_GREGS        0x28
 
+#else
+
+#error Unsupported ABI
+
 #endif
+
+#define LINUX_SC_R0_OFF   (LINUX_UC_MCONTEXT_GREGS - LINUX_UC_MCONTEXT_OFF)
+#define LINUX_SC_R1_OFF   (LINUX_SC_R0_OFF + 1*8)
+#define LINUX_SC_R2_OFF   (LINUX_SC_R0_OFF + 2*8)
+#define LINUX_SC_R3_OFF   (LINUX_SC_R0_OFF + 3*8)
+#define LINUX_SC_R4_OFF   (LINUX_SC_R0_OFF + 4*8)
+#define LINUX_SC_R5_OFF   (LINUX_SC_R0_OFF + 5*8)
+#define LINUX_SC_R6_OFF   (LINUX_SC_R0_OFF + 6*8)
+#define LINUX_SC_R7_OFF   (LINUX_SC_R0_OFF + 7*8)
+#define LINUX_SC_R8_OFF   (LINUX_SC_R0_OFF + 8*8)
+#define LINUX_SC_R9_OFF   (LINUX_SC_R0_OFF + 9*8)
+#define LINUX_SC_R10_OFF  (LINUX_SC_R0_OFF + 10*8)
+#define LINUX_SC_R11_OFF  (LINUX_SC_R0_OFF + 11*8)
+#define LINUX_SC_R12_OFF  (LINUX_SC_R0_OFF + 12*8)
+#define LINUX_SC_R13_OFF  (LINUX_SC_R0_OFF + 13*8)
+#define LINUX_SC_R14_OFF  (LINUX_SC_R0_OFF + 14*8)
+#define LINUX_SC_R15_OFF  (LINUX_SC_R0_OFF + 15*8)
+#define LINUX_SC_R16_OFF  (LINUX_SC_R0_OFF + 16*8)
+#define LINUX_SC_R17_OFF  (LINUX_SC_R0_OFF + 17*8)
+#define LINUX_SC_R18_OFF  (LINUX_SC_R0_OFF + 18*8)
+#define LINUX_SC_R19_OFF  (LINUX_SC_R0_OFF + 19*8)
+#define LINUX_SC_R20_OFF  (LINUX_SC_R0_OFF + 20*8)
+#define LINUX_SC_R21_OFF  (LINUX_SC_R0_OFF + 21*8)
+#define LINUX_SC_R22_OFF  (LINUX_SC_R0_OFF + 22*8)
+#define LINUX_SC_R23_OFF  (LINUX_SC_R0_OFF + 23*8)
+#define LINUX_SC_R24_OFF  (LINUX_SC_R0_OFF + 24*8)
+#define LINUX_SC_R25_OFF  (LINUX_SC_R0_OFF + 25*8)
+#define LINUX_SC_R26_OFF  (LINUX_SC_R0_OFF + 26*8)
+#define LINUX_SC_R27_OFF  (LINUX_SC_R0_OFF + 27*8)
+#define LINUX_SC_R28_OFF  (LINUX_SC_R0_OFF + 28*8)
+#define LINUX_SC_R29_OFF  (LINUX_SC_R0_OFF + 29*8)
+#define LINUX_SC_R30_OFF  (LINUX_SC_R0_OFF + 30*8)
+#define LINUX_SC_R31_OFF  (LINUX_SC_R0_OFF + 31*8)
+
+#define LINUX_SC_SP_OFF   LINUX_SC_R29_OFF
+#define LINUX_SC_PC_OFF   (LINUX_UC_MCONTEXT_PC - LINUX_UC_MCONTEXT_OFF)