[PATCH v2 2/5] RISCV: Arrange DELETE pass after .align pass

[Patrick O'Neill]

By moving the deletion pass after the align pass, the linker can touch
each byte once via piecewise deletion. Otherwise, it may need to move
the same bytes twice.

2022-04-29 Patrick O'Neill <patrick@rivosinc.com>

	* elfnn-riscv.c (_bfd_riscv_relax_align): Count to-be-deleted
	  bytes so the alignments are still accurate.
	* elfnn-riscv.c (_bfd_riscv_relax_section): Move DELETE pass
	  after ALIGN pass.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>
---
This gives us an O(n^2) runtime when the align pass counts the number of 
deleted bytes preceding it, but this will be fixed in Patch 4/5.
---
 bfd/elfnn-riscv.c | 45 +++++++++++++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 8f9f0d8a86a..17f9607744f 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -4435,7 +4435,7 @@ _bfd_riscv_relax_tls_le (bfd *abfd,
 static bool
 _bfd_riscv_relax_align (bfd *abfd, asection *sec,
 			asection *sym_sec,
-			struct bfd_link_info *link_info,
+			struct bfd_link_info *link_info ATTRIBUTE_UNUSED,
 			Elf_Internal_Rela *rel,
 			bfd_vma symval,
 			bfd_vma max_alignment ATTRIBUTE_UNUSED,
@@ -4449,6 +4449,18 @@ _bfd_riscv_relax_align (bfd *abfd, asection *sec,
   while (alignment <= rel->r_addend)
     alignment *= 2;
 
+  Elf_Internal_Rela *relocs = elf_section_data (sec)->relocs;
+  for (unsigned int i = 0; i < sec->reloc_count; i++)
+    {
+      Elf_Internal_Rela *reloc = relocs + i;
+      /* Ignore annotations after this alignment directive.  */
+      if (reloc == rel)
+	break;
+      /* Account for to-be-deleted bytes  */
+      else if (ELFNN_R_TYPE (reloc->r_info) == R_RISCV_DELETE)
+	symval -= reloc->r_addend;
+    }
+
   symval -= rel->r_addend;
   bfd_vma aligned_addr = ((symval - 1) & ~(alignment - 1)) + alignment;
   bfd_vma nop_bytes = aligned_addr - symval;
@@ -4468,12 +4480,12 @@ _bfd_riscv_relax_align (bfd *abfd, asection *sec,
       return false;
     }
 
-  /* Delete the reloc.  */
-  rel->r_info = ELFNN_R_INFO (0, R_RISCV_NONE);
-
-  /* If the number of NOPs is already correct, there's nothing to do.  */
+  /* If the number of NOPs is already correct, delete the reloc.  */
   if (nop_bytes == rel->r_addend)
-    return true;
+    {
+      rel->r_info = ELFNN_R_INFO (0, R_RISCV_NONE);
+      return true;
+    }
 
   /* Write as many RISC-V NOPs as we need.  */
   for (pos = 0; pos < (nop_bytes & -4); pos += 4)
@@ -4483,10 +4495,11 @@ _bfd_riscv_relax_align (bfd *abfd, asection *sec,
   if (nop_bytes % 4 != 0)
     bfd_putl16 (RVC_NOP, contents + rel->r_offset + pos);
 
-  /* Delete the excess bytes.  */
-  return riscv_relax_delete_bytes (abfd, sec, rel->r_offset + nop_bytes,
-				   rel->r_addend - nop_bytes, link_info,
-				   NULL);
+  /* Mark the excess bytes for deletion.  */
+  rel->r_info = ELFNN_R_INFO (0, R_RISCV_DELETE);
+  rel->r_addend = rel->r_addend - nop_bytes;
+  rel->r_offset = rel->r_offset + nop_bytes;
+  return true;
 }
 
 /* Relax PC-relative references to GP-relative references.  */
@@ -4677,8 +4690,8 @@ bfd_elfNN_riscv_set_data_segment_info (struct bfd_link_info *info,
 /* Relax a section.
 
    Pass 0: Shortens code sequences for LUI/CALL/TPREL/PCREL relocs.
-   Pass 1: Deletes the bytes that PCREL relaxation in pass 0 made obsolete.
-   Pass 2: Which cannot be disabled, handles code alignment directives.  */
+   Pass 1: Which cannot be disabled, handles code alignment directives.
+   Pass 2: Handle DELETE directives.  */
 
 static bool
 _bfd_riscv_relax_section (bfd *abfd, asection *sec,
@@ -4697,7 +4710,7 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
   *again = false;
 
   if (bfd_link_relocatable (info)
-      || sec->sec_flg0
+      || (sec->sec_flg0 && info->relax_pass == 0)
       || (sec->flags & SEC_RELOC) == 0
       || sec->reloc_count == 0
       || (info->disable_target_specific_optimizations
@@ -4771,10 +4784,10 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
 	  /* Skip over the R_RISCV_RELAX.  */
 	  i++;
 	}
-      else if (info->relax_pass == 1 && type == R_RISCV_DELETE)
-	relax_func = _bfd_riscv_relax_delete;
-      else if (info->relax_pass == 2 && type == R_RISCV_ALIGN)
+      else if (info->relax_pass == 1 && type == R_RISCV_ALIGN)
 	relax_func = _bfd_riscv_relax_align;
+      else if (info->relax_pass == 2 && type == R_RISCV_DELETE)
+	relax_func = _bfd_riscv_relax_delete;
       else
 	continue;
 
-- 
2.25.1