x86: correct overflow checking for 16-bit PC-relative relocs

The only insn requiring a truly 16-bit PC-relative relocation outside of
16-bit mode is XBEGIN (with an operand size override). For it, the
relocation generated should behave similar to 8- and (for 64-bit) 32-bit
PC-relatives ones, i.e. be checked for a signed value to fit the field.
This same mode is also correct for 16-bit code. Outside of 16-bit code,
branches with operand size overrides act in a truly PC-relative way only
when living in the low 32k of address space, as they truncate rIP to 16
bits. This can't be expressed by a PC-relative relocation.

Putting in place a new testcase, I'd like to note that the two existing
ones (pcrel16 and pcrel16abs) appear to be pretty pointless: They don't
expect any error despite supposedly checking for overflow, and in fact
there can't possibly be any error for the
- former since gas doesn't emit any relocation in the first place there,
- latter because the way the relocation gets expressed by gas doesn't
  allow the linker to notice the overflow; it should be detected by gas
  if at all, but see above (an error would be reported here for x86-64
  afaict, but this test doesn't get re-used there).

1 files changed, 1 insertions, 0 deletions

diff --git a/ld/testsuite/ld-i386/i386.exp b/ld/testsuite/ld-i386/i386.exp
index 6ad69a8..d0b3f69 100644
--- a/ld/testsuite/ld-i386/i386.exp
+++ b/ld/testsuite/ld-i386/i386.exp
@@ -297,6 +297,7 @@ run_dump_test "abs"
 run_dump_test "pcrel8"
 run_dump_test "pcrel16"
 run_dump_test "pcrel16abs"
+run_dump_test "pcrel16-2"
 run_dump_test "alloc"
 run_dump_test "warn1"
 run_dump_test "tlsgd2"