[PATCH] RISC-V: Do not gp relax against an ABS symbol if it is far away.

[Joseph Faulls <Joseph.Faulls@imgtec.com>]

[-- Attachment #1: Type: text/plain, Size: 3754 bytes --]

Relaxations can cause the gp to move after it has been decided to gp
relax. Against an absolute symbol, the distance may change such that the
offset can no longer fit in the 12-bit immediate field.

bfd/
        * elfnn-riscv.c (_bfd_riscv_relax_pc) Do not gp relax against and ABS
          symbol if it is far away.
ld/
        * ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
        * ld/testsuite/ld-riscv-elf/gp-relax-abs*: New testcases.
---
bfd/elfnn-riscv.c                            | 12 ++++++++++++
ld/testsuite/ld-riscv-elf/gp-relax-abs-sym.s |  3 +++
ld/testsuite/ld-riscv-elf/gp-relax-abs.d     | 14 ++++++++++++++
ld/testsuite/ld-riscv-elf/gp-relax-abs.s     |  5 +++++
ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp   |  1 +
5 files changed, 35 insertions(+)
create mode 100644 ld/testsuite/ld-riscv-elf/gp-relax-abs-sym.s
create mode 100644 ld/testsuite/ld-riscv-elf/gp-relax-abs.d
create mode 100644 ld/testsuite/ld-riscv-elf/gp-relax-abs.s

diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 09aa7be225e..79e29e8b272 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -4885,6 +4885,18 @@ _bfd_riscv_relax_pc (bfd *abfd ATTRIBUTE_UNUSED,
              max_alignment = _bfd_riscv_get_max_alignment (sec, gp);
              htab->max_alignment_for_gp = max_alignment;
            }
+         /* If the symbol is in the abs section, relaxation could cause the gp
+          * to move such that the gp relocation is no longer possible.
+          * Conservatively half the allowed distance, as it cannot be that
+          * gp moves more than this, i.e. more than half the instructions be
+          * deleted due to relaxation.  Do this by adjusting reserve_size.  */
+         if (sym_sec->output_section == bfd_abs_section_ptr)
+           {
+             if (symval >= gp)
+               reserve_size += (symval - gp) / 2;
+             else
+               reserve_size += (gp - symval) / 2;
+           }
        }
     }

diff --git a/ld/testsuite/ld-riscv-elf/gp-relax-abs-sym.s b/ld/testsuite/ld-riscv-elf/gp-relax-abs-sym.s
new file mode 100644
index 00000000000..a018bb3a50a
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-relax-abs-sym.s
@@ -0,0 +1,3 @@
+.section .data
+.globl sym
+.set sym,0x10804
diff --git a/ld/testsuite/ld-riscv-elf/gp-relax-abs.d b/ld/testsuite/ld-riscv-elf/gp-relax-abs.d
new file mode 100644
index 00000000000..2c7ab3a2579
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-relax-abs.d
@@ -0,0 +1,14 @@
+#source: gp-relax-abs.s
+#source: gp-relax-abs-sym.s
+#as: -march=rv64ic -mabi=lp64
+#ld: -Tcode-model-01.ld -melf64lriscv
+#objdump: -d
+
+.*:[   ]+file format .*
+
+Disassembly of section \.text:
+
+[0-9a-f]+ <_start>:
+.*auipc.*
+.*lw.*# [0-9a-f]* <sym>
+#pass
diff --git a/ld/testsuite/ld-riscv-elf/gp-relax-abs.s b/ld/testsuite/ld-riscv-elf/gp-relax-abs.s
new file mode 100644
index 00000000000..db2103bafd1
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-relax-abs.s
@@ -0,0 +1,5 @@
+.text
+.global _start
+_start:
+    auipc t0, %pcrel_hi(sym)
+    lw t0, %pcrel_lo(_start)(t0)
diff --git a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
index 947a266ba72..a53a2758991 100644
--- a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
+++ b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
@@ -172,6 +172,7 @@ if [istarget "riscv*-*-*"] {
     run_dump_test "attr-merge-priv-spec-failed-06"
     run_dump_test "attr-phdr"
     run_dump_test "relax-max-align-gp"
+    run_dump_test "gp-relax-abs"
     run_dump_test "uleb128"
     run_ld_link_tests [list \
        [list "Weak reference 32" "-T weakref.ld -m[riscv_choose_ilp32_emul]" "" \
--
2.34.1