gdb: LoongArch: Handle the function return value

According to LoongArch ELF ABI specification [1], handle the function
return value of various types.

[1] https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html#_return_values

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>

diff --git a/gdb/loongarch-tdep.c b/gdb/loongarch-tdep.c
index 3fb7774d8af316888740793d4b6c6de9957a9753..85a1dd70ebdc11f2dbf5353ca28886f923831a64 100644 (file)
--- a/gdb/loongarch-tdep.c
+++ b/gdb/loongarch-tdep.c
@@ -1074,6 +1074,19 @@ loongarch_push_dummy_call (struct gdbarch *gdbarch,
   return sp;
 }
 
+/* Partial transfer of a cooked register.  */
+
+static void
+loongarch_xfer_reg (struct regcache *regcache,
+                   int regnum, int len, gdb_byte *readbuf,
+                   const gdb_byte *writebuf, size_t offset)
+{
+  if (readbuf)
+    regcache->cooked_read_part (regnum, 0, len, readbuf + offset);
+  if (writebuf)
+    regcache->cooked_write_part (regnum, 0, len, writebuf + offset);
+}
+
 /* Implement the return_value gdbarch method.  */
 
 static enum return_value_convention
@@ -1081,24 +1094,216 @@ loongarch_return_value (struct gdbarch *gdbarch, struct value *function,
                        struct type *type, struct regcache *regcache,
                        gdb_byte *readbuf, const gdb_byte *writebuf)
 {
-  int len = TYPE_LENGTH (type);
-  int regnum = -1;
+  int regsize = register_size (gdbarch, 0);
+  enum type_code code = type->code ();
+  size_t len = TYPE_LENGTH (type);
+  unsigned int fixed_point_members;
+  unsigned int floating_point_members;
+  bool first_member_is_fixed_point;
+  int a0 = LOONGARCH_A0_REGNUM;
+  int a1 = LOONGARCH_A0_REGNUM + 1;
+  int f0 = LOONGARCH_FIRST_FP_REGNUM;
+  int f1 = LOONGARCH_FIRST_FP_REGNUM + 1;
 
-  /* See if our value is returned through a register.  If it is, then
-     store the associated register number in REGNUM.  */
-  switch (type->code ())
+  if (len > 2 * regsize)
+    return RETURN_VALUE_STRUCT_CONVENTION;
+
+  switch (code)
     {
-      case TYPE_CODE_INT:
-       regnum = LOONGARCH_A0_REGNUM;
-       break;
+    case TYPE_CODE_INT:
+    case TYPE_CODE_BOOL:
+    case TYPE_CODE_CHAR:
+    case TYPE_CODE_RANGE:
+    case TYPE_CODE_ENUM:
+    case TYPE_CODE_PTR:
+      {
+       /* integer or pointer type.
+          The return value is passed in a0,
+          the unsigned integer scalars are zero-extended to GRLEN bits,
+          and the signed integer scalars are sign-extended.  */
+       if (writebuf)
+         {
+           gdb_byte buf[regsize];
+           if (type->is_unsigned ())
+             {
+               ULONGEST data = extract_unsigned_integer (writebuf, len, BFD_ENDIAN_LITTLE);
+               store_unsigned_integer (buf, regsize, BFD_ENDIAN_LITTLE, data);
+             }
+           else
+             {
+               LONGEST data = extract_signed_integer (writebuf, len, BFD_ENDIAN_LITTLE);
+               store_signed_integer (buf, regsize, BFD_ENDIAN_LITTLE, data);
+             }
+           loongarch_xfer_reg (regcache, a0, regsize, nullptr, buf, 0);
+         }
+       else
+         loongarch_xfer_reg (regcache, a0, len, readbuf, nullptr, 0);
+      }
+      break;
+    case TYPE_CODE_FLT:
+      /* long double type.
+        The return value is passed in a0 and a1.  */
+      if (len == 2 * regsize)
+       {
+         loongarch_xfer_reg (regcache, a0, regsize, readbuf, writebuf, 0);
+         loongarch_xfer_reg (regcache, a1, len - regsize, readbuf, writebuf, regsize);
+       }
+      /* float or double type.
+        The return value is passed in f0.  */
+      else
+       {
+         loongarch_xfer_reg (regcache, f0, len, readbuf, writebuf, 0);
+       }
+      break;
+    case TYPE_CODE_STRUCT:
+      {
+       fixed_point_members = 0;
+       floating_point_members = 0;
+       first_member_is_fixed_point = false;
+       compute_struct_member (type,
+                              &fixed_point_members,
+                              &floating_point_members,
+                              &first_member_is_fixed_point);
+
+       if (len > 0 && len <= regsize)
+         {
+           /* The structure has only fixed-point members.  */
+           if (fixed_point_members > 0 && floating_point_members == 0)
+             {
+               /* The return value is passed in a0.  */
+               loongarch_xfer_reg (regcache, a0, len, readbuf, writebuf, 0);
+             }
+           /* The structure has only floating-point members.  */
+           else if (fixed_point_members == 0 && floating_point_members > 0)
+             {
+               /* The structure has one floating-point member.
+                  The return value is passed in f0.  */
+               if (floating_point_members == 1)
+                 {
+                   loongarch_xfer_reg (regcache, f0, len, readbuf, writebuf, 0);
+                 }
+               /* The structure has two floating-point members.
+                  The return value is passed in f0 and f1.  */
+               else if (floating_point_members == 2)
+                 {
+                   loongarch_xfer_reg (regcache, f0, len / 2, readbuf, writebuf, 0);
+                   loongarch_xfer_reg (regcache, f1, len / 2, readbuf, writebuf, len / 2);
+                 }
+             }
+           /* The structure has both fixed-point and floating-point members.  */
+           else if (fixed_point_members > 0 && floating_point_members > 0)
+             {
+               /* The structure has one float member and multiple fixed-point members.
+                  The return value is passed in a0.  */
+               if (floating_point_members == 1 && fixed_point_members > 1)
+                 {
+                   loongarch_xfer_reg (regcache, a0, len, readbuf, writebuf, 0);
+                 }
+               /* The structure has one float member and one fixed-point member.  */
+               else if (floating_point_members == 1 && fixed_point_members == 1)
+                 {
+                   /* The return value is passed in f0 and a0 if the first member is floating-point.  */
+                   if (first_member_is_fixed_point == false)
+                     {
+                       loongarch_xfer_reg (regcache, f0, regsize / 2, readbuf, writebuf, 0);
+                       loongarch_xfer_reg (regcache, a0, regsize / 2, readbuf, writebuf, regsize / 2);
+                     }
+                   /* The return value is passed in a0 and f0 if the first member is fixed-point.  */
+                   else
+                     {
+                       loongarch_xfer_reg (regcache, a0, regsize / 2, readbuf, writebuf, 0);
+                       loongarch_xfer_reg (regcache, f0, regsize / 2, readbuf, writebuf, regsize / 2);
+                     }
+                 }
+             }
+         }
+       else if (len > regsize && len <= 2 * regsize)
+         {
+           /* The structure has only fixed-point members.  */
+           if (fixed_point_members > 0 && floating_point_members == 0)
+             {
+               /* The return value is passed in a0 and a1.  */
+               loongarch_xfer_reg (regcache, a0, regsize, readbuf, writebuf, 0);
+               loongarch_xfer_reg (regcache, a1, len - regsize, readbuf, writebuf, regsize);
+             }
+           /* The structure has only floating-point members.  */
+           else if (fixed_point_members == 0 && floating_point_members > 0)
+             {
+               /* The structure has one long double member
+                  or one double member and two adjacent float members
+                  or 3-4 float members.
+                  The return value is passed in a0 and a1.  */
+               if ((len == 16 && floating_point_members == 1)
+                   || (len == 16 && floating_point_members == 3)
+                   || (len == 12 && floating_point_members == 3)
+                   || (len == 16 && floating_point_members == 4))
+                 {
+                   loongarch_xfer_reg (regcache, a0, regsize, readbuf, writebuf, 0);
+                   loongarch_xfer_reg (regcache, a1, len - regsize, readbuf, writebuf, regsize);
+                 }
+               /* The structure has two double members
+                  or one double member and one float member.
+                  The return value is passed in f0 and f1.  */
+               else if ((len == 16 && floating_point_members == 2)
+                        || (len == 12 && floating_point_members == 2))
+                 {
+                   loongarch_xfer_reg (regcache, f0, regsize, readbuf, writebuf, 0);
+                   loongarch_xfer_reg (regcache, f1, len - regsize, readbuf, writebuf, regsize);
+                 }
+             }
+           /* The structure has both fixed-point and floating-point members.  */
+           else if (fixed_point_members > 0 && floating_point_members > 0)
+             {
+               /* The structure has one floating-point member and one fixed-point member.  */
+               if (floating_point_members == 1 && fixed_point_members == 1)
+                 {
+                   /* The return value is passed in f0 and a0 if the first member is floating-point.  */
+                   if (first_member_is_fixed_point == false)
+                     {
+                       loongarch_xfer_reg (regcache, f0, regsize, readbuf, writebuf, 0);
+                       loongarch_xfer_reg (regcache, a0, len - regsize, readbuf, writebuf, regsize);
+                     }
+                   /* The return value is passed in a0 and f0 if the first member is fixed-point.  */
+                   else
+                     {
+                       loongarch_xfer_reg (regcache, a0, regsize, readbuf, writebuf, 0);
+                       loongarch_xfer_reg (regcache, f0, len - regsize, readbuf, writebuf, regsize);
+                     }
+                 }
+               else
+                 {
+                   /* The return value is passed in a0 and a1.  */
+                   loongarch_xfer_reg (regcache, a0, regsize, readbuf, writebuf, 0);
+                   loongarch_xfer_reg (regcache, a1, len - regsize, readbuf, writebuf, regsize);
+                 }
+             }
+         }
+      }
+      break;
+    case TYPE_CODE_UNION:
+      if (len > 0 && len <= regsize)
+       {
+         /* The return value is passed in a0.  */
+         loongarch_xfer_reg (regcache, a0, len, readbuf, writebuf, 0);
+       }
+      else if (len > regsize && len <= 2 * regsize)
+       {
+         /* The return value is passed in a0 and a1.  */
+         loongarch_xfer_reg (regcache, a0, regsize, readbuf, writebuf, 0);
+         loongarch_xfer_reg (regcache, a1, len - regsize, readbuf, writebuf, regsize);
+       }
+      break;
+    case TYPE_CODE_COMPLEX:
+      {
+       /* The return value is passed in f0 and f1.  */
+       loongarch_xfer_reg (regcache, f0, len / 2, readbuf, writebuf, 0);
+       loongarch_xfer_reg (regcache, f1, len / 2, readbuf, writebuf, len / 2);
+      }
+      break;
+    default:
+      break;
     }
 
-  /* Extract the return value from the register where it was stored.  */
-  if (readbuf != nullptr)
-    regcache->raw_read_part (regnum, 0, len, readbuf);
-  if (writebuf != nullptr)
-    regcache->raw_write_part (regnum, 0, len, writebuf);
-
   return RETURN_VALUE_REGISTER_CONVENTION;
 }