[PATCH v3] Support multiple .eh_frame sections

[Jojo R <rjiejie@linux.alibaba.com>]

	This patch is based on MULTIPLE_FRAME_SECTIONS and EH_FRAME_LINKONCE,
	it allows backend to enable this feature and use '--gc-sections' simply.

	* gas/dw2gencfi.h (TARGET_MULTIPLE_EH_FRAME_SECTIONS): New.
	(MULTIPLE_FRAME_SECTIONS): Add TARGET_MULTIPLE_EH_FRAME_SECTIONS.
	* gas/dw2gencfi.c (EH_FRAME_LINKONCE): Add TARGET_MULTIPLE_EH_FRAME_SECTIONS.
	(is_now_linkonce_segment): Likewise.
	(get_cfi_seg): Create relocation info between .eh_frame.* and .text.* section.

	* bfd/elf-bfd.h (elf_backend_can_make_multiple_eh_frame): New.
	* bfd/elfxx-target.h (elf_backend_can_make_multiple_eh_frame): Likewise.
	* bfd/elflink.c (_bfd_elf_default_action_discarded): Add checking for
	elf_backend_can_make_multiple_eh_frame.
---
 bfd/elf-bfd.h          |  3 +++
 bfd/elflink.c          |  7 +++++++
 bfd/elfxx-target.h     |  4 ++++
 gas/doc/internals.texi |  4 ++++
 gas/dw2gencfi.c        | 27 +++++++++++++++++++++++++--
 gas/dw2gencfi.h        |  7 ++++++-
 6 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index f00f87b2779..fa4b9bcf193 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -1432,6 +1432,9 @@ struct elf_backend_data
   bool (*elf_backend_can_make_lsda_relative_eh_frame)
      (bfd *, struct bfd_link_info *, asection *);
 
+  /* Tell linker to support multiple eh_frame sections.  */
+  bool elf_backend_can_make_multiple_eh_frame;
+
   /* This function returns an encoding after computing the encoded
      value (and storing it in ENCODED) for the given OFFSET into OSEC,
      to be stored in at LOC_OFFSET into the LOC_SEC input section.
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 89dcf26108c..019ac302905 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -10924,12 +10924,19 @@ elf_section_ignore_discarded_relocs (asection *sec)
 unsigned int
 _bfd_elf_default_action_discarded (asection *sec)
 {
+  const struct elf_backend_data *bed;
+  bed = get_elf_backend_data (sec->owner);
+
   if (sec->flags & SEC_DEBUGGING)
     return PRETEND;
 
   if (strcmp (".eh_frame", sec->name) == 0)
     return 0;
 
+  if (bed->elf_backend_can_make_multiple_eh_frame
+      && strncmp (sec->name, ".eh_frame.", 10) == 0)
+    return 0;
+
   if (strcmp (".gcc_except_table", sec->name) == 0)
     return 0;
 
diff --git a/bfd/elfxx-target.h b/bfd/elfxx-target.h
index ca600bb5ddf..f39244e7f52 100644
--- a/bfd/elfxx-target.h
+++ b/bfd/elfxx-target.h
@@ -658,6 +658,9 @@
 #ifndef elf_backend_can_make_lsda_relative_eh_frame
 #define elf_backend_can_make_lsda_relative_eh_frame	_bfd_elf_can_make_relative
 #endif
+#ifndef elf_backend_can_make_multiple_eh_frame
+#define elf_backend_can_make_multiple_eh_frame 0
+#endif
 #ifndef elf_backend_encode_eh_address
 #define elf_backend_encode_eh_address		_bfd_elf_encode_eh_address
 #endif
@@ -891,6 +894,7 @@ static const struct elf_backend_data elfNN_bed =
   elf_backend_eh_frame_address_size,
   elf_backend_can_make_relative_eh_frame,
   elf_backend_can_make_lsda_relative_eh_frame,
+  elf_backend_can_make_multiple_eh_frame,
   elf_backend_encode_eh_address,
   elf_backend_write_section,
   elf_backend_elfsym_local_is_section,
diff --git a/gas/doc/internals.texi b/gas/doc/internals.texi
index a91d2ab9c1e..f0288746d78 100644
--- a/gas/doc/internals.texi
+++ b/gas/doc/internals.texi
@@ -1581,6 +1581,10 @@ If defined, GAS will check this macro before performing any optimizations on
 the DWARF call frame debug information that is emitted.  Targets which
 implement link time relaxation may need to define this macro and set it to zero
 if it is possible to change the size of a function's prologue.
+
+@item TARGET_MULTIPLE_EH_FRAME_SECTIONS
+If defined, GAS will create multiple .eh_frame.* sections according to
+the name of owner's function sections.
 @end table
 
 @node Object format backend
diff --git a/gas/dw2gencfi.c b/gas/dw2gencfi.c
index 6be8cb50495..80b26289289 100644
--- a/gas/dw2gencfi.c
+++ b/gas/dw2gencfi.c
@@ -75,7 +75,8 @@
 # define tc_cfi_endproc(fde) ((void) (fde))
 #endif
 
-#define EH_FRAME_LINKONCE (SUPPORT_FRAME_LINKONCE || compact_eh)
+#define EH_FRAME_LINKONCE (SUPPORT_FRAME_LINKONCE || compact_eh \
+			   || TARGET_MULTIPLE_EH_FRAME_SECTIONS)
 
 #ifndef DWARF2_FORMAT
 #define DWARF2_FORMAT(SEC) dwarf2_format_32bit
@@ -277,6 +278,9 @@ is_now_linkonce_segment (void)
   if (compact_eh)
     return now_seg;
 
+  if (TARGET_MULTIPLE_EH_FRAME_SECTIONS)
+    return now_seg;
+
   if ((bfd_section_flags (now_seg)
        & (SEC_LINK_ONCE | SEC_LINK_DUPLICATES_DISCARD
 	  | SEC_LINK_DUPLICATES_ONE_ONLY | SEC_LINK_DUPLICATES_SAME_SIZE
@@ -1333,14 +1337,33 @@ static segT
 get_cfi_seg (segT cseg, const char *base, flagword flags, int align)
 {
   /* Exclude .debug_frame sections for Compact EH.  */
-  if (SUPPORT_FRAME_LINKONCE || ((flags & SEC_DEBUGGING) == 0 && compact_eh))
+  if (SUPPORT_FRAME_LINKONCE || ((flags & SEC_DEBUGGING) == 0 && compact_eh)
+      || ((flags & SEC_DEBUGGING) == 0 && TARGET_MULTIPLE_EH_FRAME_SECTIONS))
     {
+      segT iseg = cseg;
       struct dwcfi_seg_list *l;
 
       l = dwcfi_hash_find_or_make (cseg, base, flags);
 
       cseg = l->seg;
       subseg_set (cseg, l->subseg);
+
+      if (TARGET_MULTIPLE_EH_FRAME_SECTIONS
+	  && (flags & DWARF2_EH_FRAME_READ_ONLY))
+	{
+	  const frchainS *ifrch = seg_info (iseg)->frchainP;
+	  const frchainS *frch = seg_info (cseg)->frchainP;
+	  expressionS exp;
+
+	  exp.X_op = O_symbol;
+	  exp.X_add_symbol = (symbolS *) local_symbol_make (cseg->name, cseg, frch->frch_root, 0);
+	  exp.X_add_number = 0;
+	  subseg_set (iseg, ifrch->frch_subseg);
+	  fix_new_exp (ifrch->frch_root, 0, 0, &exp, 0, BFD_RELOC_NONE);
+
+	  /* Restore the original segment info.  */
+	  subseg_set (cseg, l->subseg);
+	}
     }
   else
     {
diff --git a/gas/dw2gencfi.h b/gas/dw2gencfi.h
index d570cdb8db3..0f5ae77d800 100644
--- a/gas/dw2gencfi.h
+++ b/gas/dw2gencfi.h
@@ -66,7 +66,12 @@ extern void cfi_add_CFA_restore_state (void);
 #define SUPPORT_COMPACT_EH 0
 #endif
 
-#define MULTIPLE_FRAME_SECTIONS (SUPPORT_FRAME_LINKONCE || SUPPORT_COMPACT_EH)
+#ifndef TARGET_MULTIPLE_EH_FRAME_SECTIONS
+#define TARGET_MULTIPLE_EH_FRAME_SECTIONS 0
+#endif
+
+#define MULTIPLE_FRAME_SECTIONS (SUPPORT_FRAME_LINKONCE || SUPPORT_COMPACT_EH \
+				 || TARGET_MULTIPLE_EH_FRAME_SECTIONS)
 
 struct cfi_insn_data
 {
-- 
2.17.1