MIPS coredump support

Add MIPS support to the coredump library. Explicit support for the MIPS
program counter register is added so that we can start backtracing from
the program counter value we read from a core dump. The PC register
support was not strictly required for local backtracing, and we will in
fact just plug the return address to the PC register in getcontext().

I have only tested the 32bit "OABI" paths.

configure.ac

@@ -103,7 +103,7 @@ SET_ARCH([$target_cpu],[target_arch])
 
 AC_ARG_ENABLE(coredump,
 	AS_HELP_STRING([--enable-coredump],[building libunwind-coredump library]),,
-        [AS_CASE([$host_arch], [x86*], [enable_coredump=yes], [enable_coredump=no])]
+        [AS_CASE([$host_arch], [mips*|x86*], [enable_coredump=yes], [enable_coredump=no])]
 )
 
 AC_MSG_CHECKING([if we should build libunwind-coredump])

include/libunwind-mips.h

@@ -95,6 +95,8 @@ typedef enum
     UNW_MIPS_R30,
     UNW_MIPS_R31,
 
+    UNW_MIPS_PC = 34,
+
     /* FIXME: Other registers!  */
 
     /* For MIPS, the CFA is the value of SP (r29) at the call site in the

src/coredump/_UCD_access_reg_linux.c

@@ -43,7 +43,42 @@ _UCD_access_reg (unw_addr_space_t as,
   if (regnum < 0 || regnum >= 16)
     goto badreg;
 #else
-#if defined(UNW_TARGET_X86)
+#if defined(UNW_TARGET_MIPS)
+  static const uint8_t remap_regs[] =
+    {
+      [UNW_MIPS_R0]  = EF_REG0,
+      [UNW_MIPS_R1]  = EF_REG1,
+      [UNW_MIPS_R2]  = EF_REG2,
+      [UNW_MIPS_R3]  = EF_REG3,
+      [UNW_MIPS_R4]  = EF_REG4,
+      [UNW_MIPS_R5]  = EF_REG5,
+      [UNW_MIPS_R6]  = EF_REG6,
+      [UNW_MIPS_R7]  = EF_REG7,
+      [UNW_MIPS_R8]  = EF_REG8,
+      [UNW_MIPS_R9]  = EF_REG9,
+      [UNW_MIPS_R10] = EF_REG10,
+      [UNW_MIPS_R11] = EF_REG11,
+      [UNW_MIPS_R12] = EF_REG12,
+      [UNW_MIPS_R13] = EF_REG13,
+      [UNW_MIPS_R14] = EF_REG14,
+      [UNW_MIPS_R15] = EF_REG15,
+      [UNW_MIPS_R16] = EF_REG16,
+      [UNW_MIPS_R17] = EF_REG17,
+      [UNW_MIPS_R18] = EF_REG18,
+      [UNW_MIPS_R19] = EF_REG19,
+      [UNW_MIPS_R20] = EF_REG20,
+      [UNW_MIPS_R21] = EF_REG21,
+      [UNW_MIPS_R22] = EF_REG22,
+      [UNW_MIPS_R23] = EF_REG23,
+      [UNW_MIPS_R24] = EF_REG24,
+      [UNW_MIPS_R25] = EF_REG25,
+      [UNW_MIPS_R28] = EF_REG28,
+      [UNW_MIPS_R29] = EF_REG29,
+      [UNW_MIPS_R30] = EF_REG30,
+      [UNW_MIPS_R31] = EF_REG31,
+      [UNW_MIPS_PC]  = EF_CP0_EPC,
+    };
+#elif defined(UNW_TARGET_X86)
   static const uint8_t remap_regs[] =
     {
       /* names from libunwind-x86.h */

src/mips/Gget_save_loc.c

@@ -68,6 +68,7 @@ unw_get_save_loc (unw_cursor_t *cursor, int reg, unw_save_loc_t *sloc)
     case UNW_MIPS_R29:
     case UNW_MIPS_R30:
     case UNW_MIPS_R31:
+    case UNW_MIPS_PC:
       loc = c->dwarf.loc[reg - UNW_MIPS_R0];
       break;
 

src/mips/Ginit.c

@@ -46,6 +46,8 @@ uc_addr (ucontext_t *uc, int reg)
 {
   if (reg >= UNW_MIPS_R0 && reg < UNW_MIPS_R0 + 32)
     return &uc->uc_mcontext.gregs[reg - UNW_MIPS_R0];
+  else if (reg == UNW_MIPS_PC)
+    return &uc->uc_mcontext.pc;
   else
     return NULL;
 }

src/mips/Gregs.c

@@ -69,6 +69,10 @@ tdep_access_reg (struct cursor *c, unw_regnum_t reg, unw_word_t *valp,
       loc = c->dwarf.loc[reg - UNW_MIPS_R0];
       break;
 
+    case UNW_MIPS_PC:
+      loc = c->dwarf.loc[reg];
+      break;
+
     case UNW_MIPS_CFA:
       if (write)
         return -UNW_EREADONLYREG;

src/mips/getcontext.S

@@ -1,5 +1,6 @@
 /* libunwind - a platform-independent unwind library
    Copyright (C) 2008 CodeSourcery
+   Copyright (C) 2012 Tommi Rantala <tt.rantala@gmail.com>
 
 This file is part of libunwind.
 
@@ -37,8 +38,14 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
  sw $X, (LINUX_UC_MCONTEXT_GREGS + 8 * X + OFFSET) ($4); \
  sra $1, $X, 31; \
  sw $1, (LINUX_UC_MCONTEXT_GREGS + 8 * X + 4 - OFFSET) ($4)
+/* Yes, we save the return address to PC. */
+# define SPC \
+ sw $31, (LINUX_UC_MCONTEXT_PC + OFFSET) ($4); \
+ sra $1, $31, 31; \
+ sw $1, (LINUX_UC_MCONTEXT_PC + 4 - OFFSET) ($4)
 #else
 # define SREG(X) sd $X, (LINUX_UC_MCONTEXT_GREGS + 8 * X) ($4)
+# define SPC sd $31, (LINUX_UC_MCONTEXT_PC) ($4)
 #endif
 
 	.global _Umips_getcontext
@@ -79,6 +86,7 @@ _Umips_getcontext:
 	SREG (29)
 	SREG (30)
 	SREG (31)
+	SPC
 	li	$2, 0
 	j $31
 

src/mips/init.h

@@ -34,7 +34,9 @@ common_init (struct cursor *c, unsigned use_prev_instr)
   for (i = 32; i < DWARF_NUM_PRESERVED_REGS; ++i)
     c->dwarf.loc[i] = DWARF_NULL_LOC;
 
-  ret = dwarf_get (&c->dwarf, c->dwarf.loc[31], &c->dwarf.ip);
+  c->dwarf.loc[UNW_MIPS_PC] = DWARF_REG_LOC (&c->dwarf, UNW_MIPS_PC);
+
+  ret = dwarf_get (&c->dwarf, c->dwarf.loc[UNW_MIPS_PC], &c->dwarf.ip);
   if (ret < 0)
     return ret;
 

src/mips/offsets.h

@@ -16,6 +16,7 @@
 # define LINUX_UC_STACK_OFF	0x8
 # define LINUX_UC_MCONTEXT_OFF	0x18
 # define LINUX_UC_SIGMASK_OFF	0x268
+# define LINUX_UC_MCONTEXT_PC	0x20
 # define LINUX_UC_MCONTEXT_GREGS	0x28
 
 #elif _MIPS_SIM == _ABIN32
@@ -25,6 +26,7 @@
 # define LINUX_UC_STACK_OFF	0x8
 # define LINUX_UC_MCONTEXT_OFF	0x18
 # define LINUX_UC_SIGMASK_OFF	0x270
+# define LINUX_UC_MCONTEXT_PC	0x258
 # define LINUX_UC_MCONTEXT_GREGS	0x18
 
 #elif _MIPS_SIM == _ABI64
@@ -34,6 +36,7 @@
 # define LINUX_UC_STACK_OFF	0x10
 # define LINUX_UC_MCONTEXT_OFF	0x28
 # define LINUX_UC_SIGMASK_OFF	0x280
+# define LINUX_UC_MCONTEXT_PC	0x268
 # define LINUX_UC_MCONTEXT_GREGS	0x28
 
 #endif

src/mips/regname.c

@@ -41,6 +41,8 @@ unw_regname (unw_regnum_t reg)
 {
   if (reg < (unw_regnum_t) ARRAY_SIZE (regname))
     return regname[reg];
+  else if (reg == UNW_MIPS_PC)
+    return "pc";
   else
     return "???";
 }