bpf: fix calculation when deciding to relax branch

In certain cases we were calculating the jump displacement incorrectly
when deciding whether to relax a branch.  This meant for some branches,
such as a very long backwards conditional branch, relaxation was not
done when it should have been.  The result was to error later, because
the actual jump displacement was too large to fit in the original
instruction.

This patch fixes up the displacement calculation so that those branches
are correctly relaxed and no longer result in an error.  In addition, it
changes md_convert_frag to install fixups for the JAL instructions in
the resulting relaxations rather than encoding the displacement value
directly.

gas/
	* config/tc-bpf.c (relaxed_branch_length): Correct displacement
	calculation when relaxing.
	(md_convert_frag): Likewise.  Install fixups for JAL
	instructions resulting from relaxation.
	* testsuite/gas/bpf/jump-relax-ja-be.d: Correct and expand test.
	* testsuite/gas/bpf/jump-relax-ja.d: Likewise.
	* testsuite/gas/bpf/jump-relax-ja.s: Likewise.
	* testsuite/gas/bpf/jump-relax-jump-be.d: Likewise.
	* testsuite/gas/bpf/jump-relax-jump.d: Likewise.
	* testsuite/gas/bpf/jump-relax-jump.s: Likewise.

7 files changed, 95 insertions, 43 deletions

diff --git a/gas/config/tc-bpf.c b/gas/config/tc-bpf.c
index dfa44ea..effb483 100644
--- a/gas/config/tc-bpf.c
+++ b/gas/config/tc-bpf.c
@@ -434,6 +434,7 @@ relaxed_branch_length (fragS *fragp, asection *sec, int update)
           && sec == S_GET_SEGMENT (fragp->fr_symbol))
         {
           offsetT val = S_GET_VALUE (fragp->fr_symbol) + fragp->fr_offset;
+          val -= fragp->fr_address + fragp->fr_fix;
 
           /* Convert to 64-bit words, minus one.  */
           val = (val - 8) / 8;
@@ -578,6 +579,7 @@ md_convert_frag (bfd *abfd ATTRIBUTE_UNUSED,
            && sec == S_GET_SEGMENT (fragp->fr_symbol))
     {
       offsetT val = S_GET_VALUE (fragp->fr_symbol) + fragp->fr_offset;
+      val -= fragp->fr_address + fragp->fr_fix;
       /* Convert to 64-bit blocks minus one.  */
       disp_to_target = (val - 8) / 8;
       disp_is_known = 1;
@@ -626,15 +628,27 @@ md_convert_frag (bfd *abfd ATTRIBUTE_UNUSED,
             {
               /* 16-bit disp is known and not in range.  Turn the JA
                  into a JAL with a 32-bit displacement.  */
-              char bytes[8];
+              char bytes[8] = {0};
 
               bytes[0] = ((BPF_CLASS_JMP32|BPF_CODE_JA|BPF_SRC_K) >> 56) & 0xff;
               bytes[1] = (word >> 48) & 0xff;
               bytes[2] = 0; /* disp16 high */
               bytes[3] = 0; /* disp16 lo */
-              encode_int32 ((int32_t) disp_to_target, bytes + 4);
-
               write_insn_bytes (buf, bytes);
+
+              /* Install fixup for the JAL.  */
+              reloc_howto_type *reloc_howto
+                = bfd_reloc_type_lookup (stdoutput, BFD_RELOC_BPF_DISP32);
+              if (!reloc_howto)
+                abort();
+
+              fixp = fix_new_exp (fragp, buf - (bfd_byte *) fragp->fr_literal,
+                                  bfd_get_reloc_size (reloc_howto),
+                                  &exp,
+                                  reloc_howto->pc_relative,
+                                  BFD_RELOC_BPF_DISP32);
+              fixp->fx_file = fragp->fr_file;
+              fixp->fx_line = fragp->fr_line;
             }
         }
       else
@@ -731,8 +745,23 @@ md_convert_frag (bfd *abfd ATTRIBUTE_UNUSED,
               bytes[1] = 0;
               bytes[2] = 0;
               bytes[3] = 0;
-              encode_int32 ((int32_t) disp_to_target, bytes + 4);
+              encode_int32 ((int32_t) 0, bytes + 4);
               write_insn_bytes (buf, bytes);
+
+              /* Install fixup for the JAL.  */
+              reloc_howto_type *reloc_howto
+                = bfd_reloc_type_lookup (stdoutput, BFD_RELOC_BPF_DISP32);
+              if (!reloc_howto)
+                abort();
+
+              fixp = fix_new_exp (fragp, buf - (bfd_byte *) fragp->fr_literal,
+                                  bfd_get_reloc_size (reloc_howto),
+                                  &exp,
+                                  reloc_howto->pc_relative,
+                                  BFD_RELOC_BPF_DISP32);
+              fixp->fx_file = fragp->fr_file;
+              fixp->fx_line = fragp->fr_line;
+
               buf += 8;
             }
         }
diff --git a/gas/testsuite/gas/bpf/jump-relax-ja-be.d b/gas/testsuite/gas/bpf/jump-relax-ja-be.d
index 5f07847..e5ad30d 100644
--- a/gas/testsuite/gas/bpf/jump-relax-ja-be.d
+++ b/gas/testsuite/gas/bpf/jump-relax-ja-be.d
@@ -8,10 +8,14 @@
 Disassembly of section .text:
 
 0+ <.*>:
-   0:	05 00 80 00 00 00 00 00 	ja -32768
-   8:	05 00 7f ff 00 00 00 00 	ja 32767
-  10:	05 00 ff fd 00 00 00 00 	ja -3
-  18:	05 00 00 00 00 00 00 00 	ja 0
+       0:	05 00 80 00 00 00 00 00 	ja -32768
+       8:	05 00 7f ff 00 00 00 00 	ja 32767
+      10:	05 00 ff fd 00 00 00 00 	ja -3
+      18:	05 00 00 00 00 00 00 00 	ja 0
 			18: R_BPF_GNU_64_16	undefined
-  20:	06 00 00 00 00 00 80 01 	jal 32769
-  28:	06 00 00 00 00 00 80 01 	jal 32769
+      20:	06 00 00 00 00 00 80 00 	jal 32768
+      28:	05 00 7f ff 00 00 00 00 	ja 32767
+	...
+
+0+40028 <tail>:
+   40028:	06 00 00 00 ff ff 7f fa 	jal -32774
diff --git a/gas/testsuite/gas/bpf/jump-relax-ja.d b/gas/testsuite/gas/bpf/jump-relax-ja.d
index ed3aa6b..1ac33f5 100644
--- a/gas/testsuite/gas/bpf/jump-relax-ja.d
+++ b/gas/testsuite/gas/bpf/jump-relax-ja.d
@@ -8,10 +8,14 @@
 Disassembly of section .text:
 
 0+ <.*>:
-   0:	05 00 00 80 00 00 00 00 	ja -32768
-   8:	05 00 ff 7f 00 00 00 00 	ja 32767
-  10:	05 00 fd ff 00 00 00 00 	ja -3
-  18:	05 00 00 00 00 00 00 00 	ja 0
+       0:	05 00 00 80 00 00 00 00 	ja -32768
+       8:	05 00 ff 7f 00 00 00 00 	ja 32767
+      10:	05 00 fd ff 00 00 00 00 	ja -3
+      18:	05 00 00 00 00 00 00 00 	ja 0
 			18: R_BPF_GNU_64_16	undefined
-  20:	06 00 00 00 01 80 00 00 	jal 32769
-  28:	06 00 00 00 01 80 00 00 	jal 32769
+      20:	06 00 00 00 00 80 00 00 	jal 32768
+      28:	05 00 ff 7f 00 00 00 00 	ja 32767
+	...
+
+0+40028 <tail>:
+   40028:	06 00 00 00 fa 7f ff ff 	jal -32774
diff --git a/gas/testsuite/gas/bpf/jump-relax-ja.s b/gas/testsuite/gas/bpf/jump-relax-ja.s
index f164176..61f2e61 100644
--- a/gas/testsuite/gas/bpf/jump-relax-ja.s
+++ b/gas/testsuite/gas/bpf/jump-relax-ja.s
@@ -4,13 +4,18 @@
 1:      ja -32768
         ja 32767
         /* The following instruction refers to a defined symbol that
-           is on reach, so it should not be relaxed.  */
+           is in reach, so it should not be relaxed.  */
         ja 1b
         /* The following instruction has an undefined symbol as a
            target.  It is not to be relaxed.  */
         ja undefined + 10
-        /* The following instructions refer to a defined symbol that
-           is not on reach.  They shall be relaxed to a JAL.  */
+        /* The following instruction refers to a defined symbol that
+           is not in reach, so it shall be relaxed to JAL.  */
         ja tail
-        tail = .text + 262160
+        /* Now the symbol is in reach, and the following instruction
+           shall not be relaxed.  */
         ja tail
+        .space 262136
+        tail = .
+        /* The jump back is too large and shall be relaxed.  */
+        ja 1b
diff --git a/gas/testsuite/gas/bpf/jump-relax-jump-be.d b/gas/testsuite/gas/bpf/jump-relax-jump-be.d
index 0cacdb3..5cf3bce 100644
--- a/gas/testsuite/gas/bpf/jump-relax-jump-be.d
+++ b/gas/testsuite/gas/bpf/jump-relax-jump-be.d
@@ -8,12 +8,16 @@
 Disassembly of section .text:
 
 0+ <.*>:
-   0:	1d 12 80 00 00 00 00 00 	jeq %r1,%r2,-32768
-   8:	ad 12 7f ff 00 00 00 00 	jlt %r1,%r2,32767
-  10:	bd 12 ff fd 00 00 00 00 	jle %r1,%r2,-3
-  18:	1d 12 00 01 00 00 00 00 	jeq %r1,%r2,1
-  20:	05 00 00 01 00 00 00 00 	ja 1
-  28:	06 00 00 00 00 00 80 01 	jal 32769
-  30:	2d 12 00 01 00 00 00 00 	jgt %r1,%r2,1
-  38:	05 00 00 01 00 00 00 00 	ja 1
-  40:	06 00 00 00 00 00 80 01 	jal 32769
+       0:	1d 12 80 00 00 00 00 00 	jeq %r1,%r2,-32768
+       8:	ad 12 7f ff 00 00 00 00 	jlt %r1,%r2,32767
+      10:	bd 12 ff fd 00 00 00 00 	jle %r1,%r2,-3
+      18:	1d 12 00 01 00 00 00 00 	jeq %r1,%r2,1
+      20:	05 00 00 01 00 00 00 00 	ja 1
+      28:	06 00 00 00 00 00 80 00 	jal 32768
+      30:	2d 12 7f ff 00 00 00 00 	jgt %r1,%r2,32767
+	...
+
+0+40030 <tail>:
+   40030:	55 10 00 01 00 00 00 00 	jne %r1,0,1
+   40038:	05 00 00 01 00 00 00 00 	ja 1
+   40040:	06 00 00 00 ff ff 7f f7 	jal -32777
diff --git a/gas/testsuite/gas/bpf/jump-relax-jump.d b/gas/testsuite/gas/bpf/jump-relax-jump.d
index dd31ba5..4300bf3 100644
--- a/gas/testsuite/gas/bpf/jump-relax-jump.d
+++ b/gas/testsuite/gas/bpf/jump-relax-jump.d
@@ -8,12 +8,16 @@
 Disassembly of section .text:
 
 0+ <.*>:
-   0:	1d 21 00 80 00 00 00 00 	jeq %r1,%r2,-32768
-   8:	ad 21 ff 7f 00 00 00 00 	jlt %r1,%r2,32767
-  10:	bd 21 fd ff 00 00 00 00 	jle %r1,%r2,-3
-  18:	1d 21 01 00 00 00 00 00 	jeq %r1,%r2,1
-  20:	05 00 01 00 00 00 00 00 	ja 1
-  28:	06 00 00 00 01 80 00 00 	jal 32769
-  30:	2d 21 01 00 00 00 00 00 	jgt %r1,%r2,1
-  38:	05 00 01 00 00 00 00 00 	ja 1
-  40:	06 00 00 00 01 80 00 00 	jal 32769
+       0:	1d 21 00 80 00 00 00 00 	jeq %r1,%r2,-32768
+       8:	ad 21 ff 7f 00 00 00 00 	jlt %r1,%r2,32767
+      10:	bd 21 fd ff 00 00 00 00 	jle %r1,%r2,-3
+      18:	1d 21 01 00 00 00 00 00 	jeq %r1,%r2,1
+      20:	05 00 01 00 00 00 00 00 	ja 1
+      28:	06 00 00 00 00 80 00 00 	jal 32768
+      30:	2d 21 ff 7f 00 00 00 00 	jgt %r1,%r2,32767
+	...
+
+0+40030 <tail>:
+   40030:	55 01 01 00 00 00 00 00 	jne %r1,0,1
+   40038:	05 00 01 00 00 00 00 00 	ja 1
+   40040:	06 00 00 00 f7 7f ff ff 	jal -32777
diff --git a/gas/testsuite/gas/bpf/jump-relax-jump.s b/gas/testsuite/gas/bpf/jump-relax-jump.s
index 5ea6110..6b23c56 100644
--- a/gas/testsuite/gas/bpf/jump-relax-jump.s
+++ b/gas/testsuite/gas/bpf/jump-relax-jump.s
@@ -2,11 +2,13 @@
            fix in the jump 16-bit signed displacement operand.  */
 1:      jeq %r1, %r2, -32768
         jlt %r1, %r2, 32767
-        /* The following instruction refers to a defined symbol that
-           is on reach, so it should not be relaxed.  */
+        /* The following instructions refer to defined symbols that
+           are in reach, so they should not be relaxed.  */
         jle %r1, %r2, 1b
-        /* The following instructions refer to a defined symbol that
-           is not on reach.  They shall be relaxed.  */
         jeq %r1, %r2, tail
-        tail = .text + 262160
         jgt %r1, %r2, tail
+        /* The following instructions refers to defined symbols that
+           are not in reach, so they shall be relaxied.  */
+        .space 262136
+        tail = .
+        jne %r1, 0, 1b