[PATCH] LoongArch: Disallow TLS transition when a section contains TLS_IE64 or TLS_DESC64 reloc

[Xi Ruoyao <xry111@xry111.site>]

We cannot do TLS transition for them without a psABI revision marking
some "key" instructions with reloc.  Disallow the transition when we see
such a reloc in a section to prevent an invalid "partial" transition.

Signed-off-by: Xi Ruoyao <xry111@xry111.site>
---

To Nick:

Sorry for another late update, but we need this for 2.42 or anything
compiled with -mcmodel=extreme and using errno will just blow up :(.

 bfd/elfnn-loongarch.c                         | 53 +++++++++++++++++--
 .../ld-loongarch-elf/ld-loongarch-elf.exp     | 14 +++++
 .../ld-loongarch-elf/tls-ie64-notrans.d       |  3 ++
 .../ld-loongarch-elf/tls-ie64-notrans.s       |  7 +++
 4 files changed, 73 insertions(+), 4 deletions(-)
 create mode 100644 ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d
 create mode 100644 ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s

diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
index b62bb424644..b9709401f56 100644
--- a/bfd/elfnn-loongarch.c
+++ b/bfd/elfnn-loongarch.c
@@ -717,6 +717,40 @@ loongarch_tls_transition (struct bfd_link_info *info, unsigned int r_type,
   return loongarch_tls_transition_without_check (info, r_type, h);
 }
 
+/* For TLS IE in extreme code model:
+       pcalau12i t0, %ie_pc_hi20(x)
+       li.d      t1, %ie_pc_lo12(x)
+       lu32i.d   t1, %ie64_pc_lo20(x)
+       lu52i.d   t1, t1, %ie64_pc_hi12(x)
+       ldx.d     t0, t0, t1
+   We've no idea how to remove the ldx.d instruction or turn it into a
+   nop because there is no reloc on it.  But we have to stop turning this
+   into LE or we'll end up
+       lu12i.w   t0, %le_hi20(x)
+       ori       t1, t1, %le_lo12(x)
+       lu32i.d   t1, %ie64_pc_lo20(x)
+       lu52i.d   t1, t1, %ie64_pc_hi12(x)
+       ldx.d     t0, t0, t1
+   which is completely wrong.  For TLS DESC it's similar: we cannot remove
+   the add.d instruction but we have to stop the transition.  */
+static bool
+loongarch_elf_allow_tls_transition_p (const Elf_Internal_Rela *r_begin,
+				      const Elf_Internal_Rela *r_end)
+{
+  for (; r_begin != r_end; r_begin++)
+    switch (ELFNN_R_TYPE (r_begin->r_info))
+      {
+      case R_LARCH_TLS_IE64_PC_HI12:
+      case R_LARCH_TLS_IE64_PC_LO20:
+      case R_LARCH_TLS_DESC64_PC_HI12:
+      case R_LARCH_TLS_DESC64_PC_LO20:
+	return false;
+      }
+
+  return true;
+}
+
+
 /* Look through the relocs for a section during the first phase, and
    allocate space in the global offset table or procedure linkage
    table.  */
@@ -730,6 +764,7 @@ loongarch_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
   struct elf_link_hash_entry **sym_hashes;
   const Elf_Internal_Rela *rel;
   asection *sreloc = NULL;
+  bool allow_tls_transition;
 
   if (bfd_link_relocatable (info))
     return true;
@@ -741,6 +776,9 @@ loongarch_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
   if (htab->elf.dynobj == NULL)
     htab->elf.dynobj = abfd;
 
+  allow_tls_transition = loongarch_elf_allow_tls_transition_p (
+    relocs, relocs + sec->reloc_count);
+
   for (rel = relocs; rel < relocs + sec->reloc_count; rel++)
     {
       unsigned int r_type;
@@ -818,7 +856,8 @@ loongarch_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
       int need_dynreloc = 0;
       int only_need_pcrel = 0;
 
-      r_type = loongarch_tls_transition (info, r_type, h, abfd, r_symndx);
+      if (allow_tls_transition)
+	r_type = loongarch_tls_transition (info, r_type, h, abfd, r_symndx);
       switch (r_type)
 	{
 	case R_LARCH_GOT_PC_HI20:
@@ -2632,7 +2671,6 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
 				asection **local_sections)
 {
   Elf_Internal_Rela *rel;
-  Elf_Internal_Rela *relend;
   bool fatal = false;
   asection *sreloc = elf_section_data (input_section)->sreloc;
   struct loongarch_elf_link_hash_table *htab = loongarch_elf_hash_table (info);
@@ -2643,8 +2681,10 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
   bool is_dyn = elf_hash_table (info)->dynamic_sections_created;
   asection *plt = htab->elf.splt ? htab->elf.splt : htab->elf.iplt;
   asection *got = htab->elf.sgot;
+  Elf_Internal_Rela *relend = relocs + input_section->reloc_count;
+  bool allow_tls_transition =
+    loongarch_elf_allow_tls_transition_p (relocs, relend);
 
-  relend = relocs + input_section->reloc_count;
   for (rel = relocs; rel < relend; rel++)
     {
       unsigned int r_type = ELFNN_R_TYPE (rel->r_info);
@@ -2789,7 +2829,12 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
 
       BFD_ASSERT (!resolved_local || defined_local);
 
-      relaxed_r_type = loongarch_tls_transition (info, r_type, h, input_bfd, r_symndx);
+      relaxed_r_type =
+	(allow_tls_transition ? loongarch_tls_transition (info, r_type,
+							  h, input_bfd,
+							  r_symndx)
+			      : r_type);
+
       if (relaxed_r_type != r_type)
       {
 	howto = loongarch_elf_rtype_to_howto (input_bfd, relaxed_r_type);
diff --git a/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp b/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp
index 2ff06d62236..9e35940f5d6 100644
--- a/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp
+++ b/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp
@@ -88,6 +88,20 @@ if [istarget "loongarch64-*-*"] {
 	      "medium-call" \
 	  ] \
       ]
+
+  run_ld_link_tests \
+      [list \
+	  [list \
+	      "disable TLS IE transition with TLS_IE64_PC reloc" \
+	      "-e 0x0" "" \
+	      "" \
+	      {tls-ie64-notrans.s} \
+	      [list \
+		  [list objdump -D tls-ie64-notrans.d] \
+	      ] \
+	      "tls-ie64-notrans" \
+	  ] \
+      ]
 }
 
 if [istarget "loongarch64-*-*"] {
diff --git a/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d
new file mode 100644
index 00000000000..47d507a0538
--- /dev/null
+++ b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d
@@ -0,0 +1,3 @@
+#...
+.*pcalau12i.*
+#pass
diff --git a/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s
new file mode 100644
index 00000000000..cd8c65ff9d3
--- /dev/null
+++ b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s
@@ -0,0 +1,7 @@
+# it had segfaulted the linker due to invalid IE->LE transition
+.globl _start
+_start:
+  la.tls.ie $a0, $a1, foo
+
+.section .tdata
+foo: .word 114514
-- 
2.43.0