BFD: Fix the bug of R_LARCH_AGLIN caused by discard section

To represent the first and third expression of .align, R_LARCH_ALIGN need to
associate with a symbol. We define a local symbol for R_LARCH_AGLIN.
But if the section of the local symbol is discarded, it may result in
a undefined symbol error.

Instead, we use the section name symbols, and this does not need to
add extra symbols.

During partial linking (ld -r), if the symbol associated with a relocation is
STT_SECTION type, the addend of relocation needs to add the section output
offset. We prevent it for R_LARCH_ALIGN.

The elf_backend_data.rela_normal only can set all relocations of a target to
rela_normal. Add a new function is_rela_normal to elf_backend_data, it can
set part of relocations to rela_normal.

bfd/elf-bfd.h

@@ -1721,6 +1721,10 @@ struct elf_backend_data
      backend relocate_section routine for relocatable linking.  */
   unsigned rela_normal : 1;
 
+  /* Whether a relocation is rela_normal. Compared with rela_normal,
+     is_rela_normal can set part of relocations to rela_normal.  */
+  bool (*is_rela_normal) (Elf_Internal_Rela *);
+
   /* Set if DT_REL/DT_RELA/DT_RELSZ/DT_RELASZ should not include PLT
      relocations.  */
   unsigned dtrel_excludes_plt : 1;

bfd/elflink.c

@@ -11692,7 +11692,10 @@ elf_link_input_bfd (struct elf_final_link_info *flinfo, bfd *input_bfd)
 		    {
 		      rel_hash = PTR_ADD (esdo->rela.hashes, esdo->rela.count);
 		      rela_hash_list = rel_hash;
-		      rela_normal = bed->rela_normal;
+		      if (bed->is_rela_normal != NULL)
+			rela_normal = bed->is_rela_normal (irela);
+		      else
+			rela_normal = bed->rela_normal;
 		    }
 
 		  irela->r_offset = _bfd_elf_section_offset (output_bfd,

bfd/elfnn-loongarch.c

@@ -5454,6 +5454,21 @@ elf_loongarch64_hash_symbol (struct elf_link_hash_entry *h)
   return _bfd_elf_hash_symbol (h);
 }
 
+/* If a relocation is rela_normal and the symbol associated with the
+   relocation is STT_SECTION type, the addend of the relocation would add
+   sec->output_offset when partial linking (ld -r).
+   See elf_backend_data.rela_normal and elf_link_input_bfd().
+   The addend of R_LARCH_ALIGN is used to represent the first and third
+   expression of .align, it should be a constant when linking.  */
+
+static bool
+loongarch_elf_is_rela_normal (Elf_Internal_Rela *rel)
+{
+  if (R_LARCH_ALIGN == ELFNN_R_TYPE (rel->r_info))
+    return false;
+  return true;
+}
+
 #define TARGET_LITTLE_SYM loongarch_elfNN_vec
 #define TARGET_LITTLE_NAME "elfNN-loongarch"
 #define ELF_ARCH bfd_arch_loongarch
@@ -5489,6 +5504,7 @@ elf_loongarch64_hash_symbol (struct elf_link_hash_entry *h)
 #define elf_backend_grok_psinfo loongarch_elf_grok_psinfo
 #define elf_backend_hash_symbol elf_loongarch64_hash_symbol
 #define bfd_elfNN_bfd_relax_section loongarch_elf_relax_section
+#define elf_backend_is_rela_normal loongarch_elf_is_rela_normal
 
 #define elf_backend_dtrel_excludes_plt 1
 

bfd/elfxx-target.h

@@ -709,6 +709,10 @@
 #define elf_backend_rela_normal 0
 #endif
 
+#ifndef elf_backend_is_rela_normal
+#define elf_backend_is_rela_normal NULL
+#endif
+
 #ifndef elf_backend_dtrel_excludes_plt
 #define elf_backend_dtrel_excludes_plt 0
 #endif
@@ -955,6 +959,7 @@ static const struct elf_backend_data elfNN_bed =
   elf_backend_default_use_rela_p,
   elf_backend_rela_plts_and_copies_p,
   elf_backend_rela_normal,
+  elf_backend_is_rela_normal,
   elf_backend_dtrel_excludes_plt,
   elf_backend_sign_extend_vma,
   elf_backend_want_got_plt,

gas/config/tc-loongarch.c

@@ -1791,10 +1791,7 @@ loongarch_frag_align_code (int n, int max)
      if (fragP->fr_subtype != 0 && offset > fragP->fr_subtype).  */
   if (max > 0 && (bfd_vma) max < worst_case_bytes)
     {
-      s = symbol_find (".Lla-relax-align");
-      if (s == NULL)
-	s = (symbolS *)local_symbol_make (".Lla-relax-align", now_seg,
-					  &zero_address_frag, 0);
+      s = symbol_find (now_seg->name);
       ex.X_add_symbol = s;
       ex.X_op = O_symbol;
       ex.X_add_number = (max << 8) | n;

gas/testsuite/gas/loongarch/relax_align.d

@@ -7,7 +7,7 @@
 
 Disassembly of section .text:
 
-[ 	]*0000000000000000 <.Lla-relax-align>:
+[ 	]*0000000000000000 <.text>:
 [ 	]+0:[ 	]+4c000020[ 	]+ret
 [ 	]+4:[ 	]+03400000[ 	]+nop
 [ 	]+4: R_LARCH_ALIGN[ 	]+\*ABS\*\+0xc
@@ -20,12 +20,12 @@ Disassembly of section .text:
 [ 	]+1c:[ 	]+03400000[ 	]+nop
 [ 	]+20:[ 	]+4c000020[ 	]+ret
 [ 	]+24:[ 	]+03400000[ 	]+nop
-[ 	]+24: R_LARCH_ALIGN[ 	]+.Lla-relax-align\+0x104
+[ 	]+24: R_LARCH_ALIGN[ 	]+.text\+0x104
 [ 	]+28:[ 	]+03400000[ 	]+nop
 [ 	]+2c:[ 	]+03400000[ 	]+nop
 [ 	]+30:[ 	]+4c000020[ 	]+ret
 [ 	]+34:[ 	]+03400000[ 	]+nop
-[ 	]+34: R_LARCH_ALIGN[ 	]+.Lla-relax-align\+0xb04
+[ 	]+34: R_LARCH_ALIGN[ 	]+.text\+0xb04
 [ 	]+38:[ 	]+03400000[ 	]+nop
 [ 	]+3c:[ 	]+03400000[ 	]+nop
 [ 	]+40:[ 	]+4c000020[ 	]+ret

ld/testsuite/ld-loongarch-elf/relax-align-discard.lds

@@ -0,0 +1,4 @@
+SECTIONS
+{
+  /DISCARD/ : { *(.another.*) }
+}

ld/testsuite/ld-loongarch-elf/relax-align-discard.s

@@ -0,0 +1,17 @@
+# Use the section name symbol for R_LARCH_ALIGN to avoid discard section problem
+.section ".another.text", "ax"
+.cfi_startproc
+break 0
+.cfi_def_cfa_offset 16
+.p2align 5
+break 1
+.cfi_endproc
+
+.text
+.cfi_startproc
+break 0
+.cfi_def_cfa_offset 16
+.p2align 5
+break 1
+.cfi_endproc
+

ld/testsuite/ld-loongarch-elf/relax.exp

@@ -295,6 +295,18 @@ if [istarget loongarch64-*-*] {
 		"relax-align" \
 	    ] \
 	]
+
+    run_ld_link_tests \
+      [list \
+	[list \
+	  "loongarch relax align discard" \
+	  "-e 0x0 -T relax-align-discard.lds -r" "" \
+	  "" \
+	  {relax-align-discard.s} \
+	  {} \
+	  "relax-align-discard" \
+	] \
+      ]
   }
 
   set objdump_flags "-s -j .data"