[lld][RISCV] Print error when encountering R_RISCV_ALIGN

Summary:
Unlike R_RISCV_RELAX, which is a linker hint, R_RISCV_ALIGN requires the
support of the linker even when ignoring all R_RISCV_RELAX relocations.
This is because the compiler emits as many NOPs as may be required for
the requested alignment, more than may be required pre-relaxation, to
allow for the target becoming more unaligned after relaxing earlier
sequences. This means that the target is often not initially aligned in
the object files, and so the R_RISCV_ALIGN relocations cannot just be
ignored. Since we do not support linker relaxation, we must turn these
into errors.

Reviewers: ruiu, MaskRay, espindola

Reviewed By: MaskRay

Subscribers: grimar, Jim, emaste, arichardson, asb, rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, psnobl, benna, lenary, s.egerton, pzheng, sameer.abuasal, apazos, luismarques, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71820

(cherry picked from commit d1da63664f4e42191daf2e6a9fa682ca9f75ef5e)

1 files changed, 12 insertions, 0 deletions

diff --git a/lld/test/ELF/riscv-reloc-align.s b/lld/test/ELF/riscv-reloc-align.s
new file mode 100644
index 00000000000..5103066caa3
--- /dev/null
+++ b/lld/test/ELF/riscv-reloc-align.s
@@ -0,0 +1,12 @@
+# REQUIRES: riscv
+
+# RUN: llvm-mc -filetype=obj -triple=riscv32 -mattr=+relax %s -o %t.o
+# RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK: relocation R_RISCV_ALIGN requires unimplemented linker relaxation
+
+.global _start
+_start:
+    nop
+    .balign 8
+    nop