m68k: tag floating-point ABI used

This patch adds GNU attribute support to m68k and utilises it to tag the
floating-point calling convention used (hard-float or soft-float). It enables
the linker to ensure linked objects use a consistent floating-point ABI and
allows tools like GDB to infer the ABI used from the ELF file. It is based on
similar work done for PowerPC.

bfd/
	* elf32-m68k.c (m68k_elf_merge_obj_attributes): New function.
	(elf32_m68k_merge_private_bfd_data): Merge GNU attributes.
binutils/
	* readelf.c (display_m68k_gnu_attribute): New function.
	(process_arch_specific): Call display_m68k_gnu_attribute for EM_68K.
gas/
	* config/tc-m68k.c (m68k_elf_gnu_attribute): New function.
	(md_pseudo_table): Handle "gnu_attribute".
	* doc/as.texi: Document GNU attribute for M68K.
include/
	* elf/m68k.h: Add enum for GNU object attribute with floating point
	tag name and values.
ld/
	* testsuite/ld-m68k/attr-gnu-4-0.s: New file.
	* testsuite/ld-m68k/attr-gnu-4-1.s: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-2.s: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-00.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-01.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-02.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-10.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-11.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-12.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-20.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-21.d: Likewise.
	* testsuite/ld-m68k/attr-gnu-4-22.d: Likewise.
	* testsuite/ld-m68k/m68k.exp: Run the new tests.

bfd/ChangeLog

@@ -1,3 +1,8 @@
+2020-06-26  Pat Bernardi  <bernardi@adacore.com>
+
+	* elf32-m68k.c (m68k_elf_merge_obj_attributes): New function.
+	(elf32_m68k_merge_private_bfd_data): Merge GNU attributes.
+
 2020-06-26  Alan Modra  <amodra@gmail.com>
 
 	* elfxx-riscv.c (struct priv_spec_t, priv_specs),

bfd/elf32-m68k.c

@@ -1122,6 +1122,65 @@ elf32_m68k_set_private_flags (bfd *abfd, flagword flags)
   return TRUE;
 }
 
+/* Merge object attributes from IBFD into OBFD.  Warn if
+   there are conflicting attributes. */
+static bfd_boolean
+m68k_elf_merge_obj_attributes (bfd *ibfd, struct bfd_link_info *info)
+{
+  bfd *obfd = info->output_bfd;
+  obj_attribute *in_attr, *in_attrs;
+  obj_attribute *out_attr, *out_attrs;
+  bfd_boolean ret = TRUE;
+
+  in_attrs = elf_known_obj_attributes (ibfd)[OBJ_ATTR_GNU];
+  out_attrs = elf_known_obj_attributes (obfd)[OBJ_ATTR_GNU];
+
+  in_attr = &in_attrs[Tag_GNU_M68K_ABI_FP];
+  out_attr = &out_attrs[Tag_GNU_M68K_ABI_FP];
+
+  if (in_attr->i != out_attr->i)
+    {
+      int in_fp = in_attr->i & 3;
+      int out_fp = out_attr->i & 3;
+      static bfd *last_fp;
+
+      if (in_fp == 0)
+	;
+      else if (out_fp == 0)
+	{
+	  out_attr->type = ATTR_TYPE_FLAG_INT_VAL;
+	  out_attr->i ^= in_fp;
+	  last_fp = ibfd;
+	}
+      else if (out_fp == 1 && in_fp == 2)
+	{
+	  _bfd_error_handler
+	    /* xgettext:c-format */
+	    (_("%pB uses hard float, %pB uses soft float"),
+	     last_fp, ibfd);
+	  ret = FALSE;
+	}
+      else if (out_fp == 2 && in_fp == 1)
+	{
+	  _bfd_error_handler
+	    /* xgettext:c-format */
+	    (_("%pB uses hard float, %pB uses soft float"),
+	     ibfd, last_fp);
+	  ret = FALSE;
+	}
+    }
+
+  if (!ret)
+    {
+      out_attr->type = ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_ERROR;
+      bfd_set_error (bfd_error_bad_value);
+      return FALSE;
+    }
+
+  /* Merge Tag_compatibility attributes and any common GNU ones.  */
+  return _bfd_elf_merge_object_attributes (ibfd, info);
+}
+
 /* Merge backend specific data from an object file to the output
    object file when linking.  */
 static bfd_boolean
@@ -1149,6 +1208,9 @@ elf32_m68k_merge_private_bfd_data (bfd *ibfd, struct bfd_link_info *info)
 
   bfd_set_arch_mach (obfd, bfd_arch_m68k, arch_info->mach);
 
+  if (!m68k_elf_merge_obj_attributes (ibfd, info))
+    return FALSE;
+
   in_flags = elf_elfheader (ibfd)->e_flags;
   if (!elf_flags_init (obfd))
     {

binutils/ChangeLog

@@ -1,3 +1,8 @@
+2020-06-26  Pat Bernardi  <bernardi@adacore.com>
+
+	* readelf.c (display_m68k_gnu_attribute): New function.
+	(process_arch_specific): Call display_m68k_gnu_attribute for EM_68K.
+
 2020-06-23  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR binutils/26160

binutils/readelf.c

@@ -15367,6 +15367,44 @@ display_gnu_attribute (unsigned char * p,
   return display_tag_value (tag, p, end);
 }
 
+static unsigned char *
+display_m68k_gnu_attribute (unsigned char * p,
+			    unsigned int tag,
+			    const unsigned char * const end)
+{
+  unsigned int val;
+
+  if (tag == Tag_GNU_M68K_ABI_FP)
+    {
+      printf ("  Tag_GNU_M68K_ABI_FP: ");
+      if (p == end)
+	{
+	  printf (_("<corrupt>\n"));
+	  return p;
+	}
+      READ_ULEB (val, p, end);
+
+      if (val > 3)
+	printf ("(%#x), ", val);
+
+      switch (val & 3)
+	{
+	case 0:
+	  printf (_("unspecified hard/soft float\n"));
+	  break;
+	case 1:
+	  printf (_("hard float\n"));
+	  break;
+	case 2:
+	  printf (_("soft float\n"));
+	  break;
+	}
+      return p;
+    }
+
+  return display_tag_value (tag & 1, p, end);
+}
+
 static unsigned char *
 display_power_gnu_attribute (unsigned char * p,
 			     unsigned int tag,
@@ -19928,6 +19966,10 @@ process_arch_specific (Filedata * filedata)
     case EM_NDS32:
       return process_nds32_specific (filedata);
 
+    case EM_68K:
+      return process_attributes (filedata, NULL, SHT_GNU_ATTRIBUTES, NULL,
+				 display_m68k_gnu_attribute);
+
     case EM_PPC:
     case EM_PPC64:
       return process_attributes (filedata, NULL, SHT_GNU_ATTRIBUTES, NULL,

gas/ChangeLog

@@ -1,3 +1,9 @@
+2020-06-26  Pat Bernardi  <bernardi@adacore.com>
+
+	* config/tc-m68k.c (m68k_elf_gnu_attribute): New function.
+	(md_pseudo_table): Handle "gnu_attribute".
+	* doc/as.texi: Document GNU attribute for M68K.
+
 2020-06-25  Nick Clifton  <nickc@redhat.com>
 
 	PR 26141

gas/config/tc-m68k.c

@@ -30,6 +30,7 @@
 #include "elf/m68k.h"
 
 static void m68k_elf_cons (int);
+static void m68k_elf_gnu_attribute (int);
 
 /* This string holds the chars that always start a comment.  If the
    pre-processor is disabled, these aren't very useful.  The macro
@@ -889,6 +890,7 @@ const pseudo_typeS md_pseudo_table[] =
 
   {"arch", s_m68k_arch, 0},
   {"cpu", s_m68k_cpu, 0},
+  {"gnu_attribute", m68k_elf_gnu_attribute, 0},
 
   /* The following pseudo-ops are supported for MRI compatibility.  */
   {"chip", s_chip, 0},
@@ -7951,6 +7953,24 @@ m68k_elf_cons (int nbytes /* 4=.long */)
   demand_empty_rest_of_line ();
 }
 
+/* Parse a .gnu_attribute directive.  */
+static void
+m68k_elf_gnu_attribute (int ignored ATTRIBUTE_UNUSED)
+{
+  int tag = obj_elf_vendor_attribute (OBJ_ATTR_GNU);
+
+  /* Check validity of defined m68k tags.  */
+  if (tag == Tag_GNU_M68K_ABI_FP)
+    {
+      unsigned int val;
+
+      val = bfd_elf_get_obj_attr_int (stdoutput, OBJ_ATTR_GNU, tag);
+
+      if (tag == Tag_GNU_M68K_ABI_FP && val > 2)
+	as_warn (_("unknown .gnu_attribute value"));
+    }
+}
+
 int
 tc_m68k_regname_to_dw2regnum (const char *regname)
 {

gas/doc/as.texi

@@ -7583,6 +7583,22 @@ than 1, the file can only be processed by other toolchains under some private
 arrangement indicated by the flag value and the vendor name.
 @end table
 
+@subsection M680x0 Attributes
+
+@table @r
+@item Tag_GNU_M68K_ABI_FP (4)
+The floating-point ABI used by this object file.  The value will be:
+
+@itemize @bullet
+@item
+0 for files not affected by the floating-point ABI.
+@item
+1 for files using double-precision hardware floating-point ABI.
+@item
+2 for files using the software floating-point ABI.
+@end itemize
+@end table
+
 @subsection MIPS Attributes
 
 @table @r

include/ChangeLog

@@ -1,3 +1,8 @@
+2020-06-26  Pat Bernardi  <bernardi@adacore.com>
+
+	* elf/m68k.h: Add enum for GNU object attribute with floating point
+	tag name and values.
+
 2020-06-25  Nick Clifton  <nickc@redhat.com>
 
 	* libiberty.h (bsearch_r): Remove use of the register keyword from

include/elf/m68k.h

@@ -97,5 +97,17 @@ END_RELOC_NUMBERS (R_68K_max)
 #define EF_M68K_CF_EMAC_B	0x30  /* EMAC_B */
 #define EF_M68K_CF_FLOAT	0x40  /* Has float insns */
 #define EF_M68K_CF_MASK		0xFF
-     
+
+/* GNU object attribute tags.  */
+enum
+{
+  /* 0-3 are generic.  */
+
+  /* FP ABI, low 2 bits:
+     1 for double precision hard-float,
+     2 for soft-float,
+     0 for not tagged or not using any ABIs affected by the differences. */
+  Tag_GNU_M68K_ABI_FP = 4,
+};
+
 #endif

ld/ChangeLog

@@ -1,3 +1,19 @@
+2020-06-26  Pat Bernardi  <bernardi@adacore.com>
+
+	* testsuite/ld-m68k/attr-gnu-4-0.s: New file.
+	* testsuite/ld-m68k/attr-gnu-4-1.s: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-2.s: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-00.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-01.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-02.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-10.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-11.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-12.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-20.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-21.d: Likewise.
+	* testsuite/ld-m68k/attr-gnu-4-22.d: Likewise.
+	* testsuite/ld-m68k/m68k.exp: Run the new tests.
+
 2020-06-24  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR ld/26165

ld/testsuite/ld-m68k/attr-gnu-4-0.s

@@ -0,0 +1 @@
+.gnu_attribute 4,0

ld/testsuite/ld-m68k/attr-gnu-4-00.d

@@ -0,0 +1,4 @@
+#source: attr-gnu-4-0.s
+#source: attr-gnu-4-0.s
+#ld: -r
+#readelf: -A

ld/testsuite/ld-m68k/attr-gnu-4-01.d

@@ -0,0 +1,8 @@
+#source: attr-gnu-4-0.s
+#source: attr-gnu-4-1.s
+#ld: -r
+#readelf: -A
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_M68K_ABI_FP: hard float

ld/testsuite/ld-m68k/attr-gnu-4-02.d

@@ -0,0 +1,8 @@
+#source: attr-gnu-4-0.s
+#source: attr-gnu-4-2.s
+#ld: -r
+#readelf: -A
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_M68K_ABI_FP: soft float

ld/testsuite/ld-m68k/attr-gnu-4-1.s

@@ -0,0 +1 @@
+.gnu_attribute 4,1

ld/testsuite/ld-m68k/attr-gnu-4-10.d

@@ -0,0 +1,8 @@
+#source: attr-gnu-4-1.s
+#source: attr-gnu-4-0.s
+#ld: -r
+#readelf: -A
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_M68K_ABI_FP: hard float

ld/testsuite/ld-m68k/attr-gnu-4-11.d

@@ -0,0 +1,8 @@
+#source: attr-gnu-4-1.s
+#source: attr-gnu-4-1.s
+#ld: -r
+#readelf: -A
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_M68K_ABI_FP: hard float

ld/testsuite/ld-m68k/attr-gnu-4-12.d

@@ -0,0 +1,4 @@
+#source: attr-gnu-4-1.s
+#source: attr-gnu-4-2.s
+#ld: -r
+#error: .* uses hard float, .* uses soft float.*

ld/testsuite/ld-m68k/attr-gnu-4-2.s

@@ -0,0 +1 @@
+.gnu_attribute 4,2

ld/testsuite/ld-m68k/attr-gnu-4-20.d

@@ -0,0 +1,8 @@
+#source: attr-gnu-4-2.s
+#source: attr-gnu-4-0.s
+#ld: -r
+#readelf: -A
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_M68K_ABI_FP: soft float

ld/testsuite/ld-m68k/attr-gnu-4-21.d

@@ -0,0 +1,4 @@
+#source: attr-gnu-4-2.s
+#source: attr-gnu-4-1.s
+#ld: -r
+#error: .* uses hard float, .* uses soft float.*

ld/testsuite/ld-m68k/attr-gnu-4-22.d

@@ -0,0 +1,8 @@
+#source: attr-gnu-4-2.s
+#source: attr-gnu-4-2.s
+#ld: -r
+#readelf: -A
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_M68K_ABI_FP: soft float

ld/testsuite/ld-m68k/m68k.exp

@@ -92,3 +92,13 @@ if { [istarget m68k-*-linux*] } then {
 
     run_ld_link_tests $m68k_tls_tests
 }
+
+run_dump_test "attr-gnu-4-00"
+run_dump_test "attr-gnu-4-01"
+run_dump_test "attr-gnu-4-02"
+run_dump_test "attr-gnu-4-10"
+run_dump_test "attr-gnu-4-11"
+run_dump_test "attr-gnu-4-12"
+run_dump_test "attr-gnu-4-20"
+run_dump_test "attr-gnu-4-21"
+run_dump_test "attr-gnu-4-22"