From: Indu Bhagat <indu.bhagat@oracle.com>
Date: Sat, 12 Jul 2025 06:32:58 +0000 (-0700)
Subject: gas: elf: binutils: add new section type SHT_GNU_SFRAME
X-Git-Tag: binutils-2_45~61
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6ab3f09a682a;p=thirdparty%2Fbinutils-gdb.git

gas: elf: binutils: add new section type SHT_GNU_SFRAME

So far, SFrame sections were of type SHT_PROGBITS.

As per ELF specification, SHT_PROGBITS indicates that the section holds
information defined by the program, whose format and meaning are
determined solely by the program.

On the linker side, SHT_PROGBITS should be reserved for the simple "cat
contents after applying relocs" semantics.

Currently, the only way to know that a section contains SFrame stack
trace data is if consumer checks for section name.  Such a check for
section name is not quite conformant to ELF principles.

Some of this was discussed here
https://sourceware.org/pipermail/binutils/2025-March/140181.html

With this change, the SFrame sections generated by gas, ld will have
section type set to SHT_GNU_SFRAME.   The new section type is defined in
the SHT_LOOS/SHT_HIOS space.  The SFrame parsing routine
_bfd_elf_parse_sframe () now admits sections only when the the section
type is SHT_GNU_SFRAME.

No special handling / validation is done at the moment for the case of
manual creation of SFrame sections via obj_elf_section ().  Add function
level comments for now to add a note about this.

Although the default handling for (sh_type >= SHT_LOOS && sh_type <=
SHT_HIOS) is sufficient when SHT_GNU_SFRAME is in that range, it makes
sense to add it as a case of its own.

bfd/
	* elf-sframe.c (_bfd_elf_parse_sframe): Check if section type is
	SHT_GNU_SFRAME.
	(_bfd_elf_set_section_sframe): Set SHT_GNU_SFRAME for output
	SFrame section.
	* elflink.c (obj_elf_section): Use section type for check
	instead of section name.
	* elfxx-x86.c: Set SHT_GNU_SFRAME for SFrame sections for
	.plt* sections.
	* elf.c (bfd_section_from_shdr): Add case for SHT_GNU_SFRAME.
binutils/
	* readelf.c (get_os_specific_section_type_name): Add
	SHT_GNU_SFRAME.
gas/
	* NEWS: Announce emitted SFrame sections have SHT_GNU_SFRAME
	set.
	* config/obj-elf.c (obj_elf_attach_to_group): Add comments to
	indicate no special handling for SFrame yet.
	* dw2gencfi.c (cfi_finish): Set SHT_GNU_SFRAME for emitted
	SFrame section.
ld/
	* NEWS: Announce emitted SFrame sections have SHT_GNU_SFRAME
	set.
gas/testsuite/
	* gas/cfi-sframe/cfi-sframe.exp: Add new test.
	* gas/cfi-sframe/cfi-sframe-common-1b.d: New test.
	* gas/cfi-sframe/cfi-sframe-common-1b.s: New test.
include/
	* elf/common.h (SHT_GNU_SFRAME): Add new section type for SFrame
	stack trace information.
libsframe/doc/
	* sframe-spec.texi: Add expected ELF section type.
---

diff --git a/bfd/elf-sframe.c b/bfd/elf-sframe.c
index d74235b030a..b709e590a2d 100644
--- a/bfd/elf-sframe.c
+++ b/bfd/elf-sframe.c
@@ -191,6 +191,18 @@ _bfd_elf_parse_sframe (bfd *abfd,
   bfd_size_type sf_size;
   int decerr = 0;
 
+  /* Prior versions of assembler and ld were generating SFrame sections with
+     section type SHT_PROGBITS.  Issue an error for lack of support for such
+     objects now.  Even if section size is zero, a valid section type is
+     expected.  */
+  if (elf_section_type (sec) != SHT_GNU_SFRAME)
+    {
+      _bfd_error_handler
+	(_("error in %pB(%pA); unexpected SFrame section type"),
+	 abfd, sec);
+      return false;
+    }
+
   if (sec->size == 0
       || (sec->flags & SEC_HAS_CONTENTS) == 0
       || sec->sec_info_type != SEC_INFO_TYPE_NONE)
@@ -298,8 +310,7 @@ _bfd_elf_discard_section_sframe
    BFD ABFD.  Returns true if no error.  */
 
 bool
-_bfd_elf_set_section_sframe (bfd *abfd,
-				struct bfd_link_info *info)
+_bfd_elf_set_section_sframe (bfd *abfd, struct bfd_link_info *info)
 {
   asection *cfsec;
 
@@ -307,6 +318,7 @@ _bfd_elf_set_section_sframe (bfd *abfd,
   if (!cfsec)
     return false;
 
+  elf_section_type (cfsec) = SHT_GNU_SFRAME;
   elf_sframe (abfd) = cfsec;
 
   return true;
diff --git a/bfd/elf.c b/bfd/elf.c
index 1eba14283f8..ba0e313524d 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -2476,6 +2476,7 @@ bfd_section_from_shdr (bfd *abfd, unsigned int shindex)
     case SHT_PREINIT_ARRAY:	/* .preinit_array section.  */
     case SHT_GNU_LIBLIST:	/* .gnu.liblist section.  */
     case SHT_GNU_HASH:		/* .gnu.hash section.  */
+    case SHT_GNU_SFRAME:	/* .sframe section.  */
       ret = _bfd_elf_make_section_from_shdr (abfd, hdr, name, shindex);
       goto success;
 
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 666399bc680..c4f57cf2f3c 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -11293,7 +11293,7 @@ _bfd_elf_default_action_discarded (asection *sec)
       && strncmp (sec->name, ".eh_frame.", 10) == 0)
     return 0;
 
-  if (strcmp (".sframe", sec->name) == 0)
+  if (elf_section_type (sec) == SHT_GNU_SFRAME)
     return 0;
 
   if (strcmp (".gcc_except_table", sec->name) == 0)
diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index 663f40ae7f0..3dc00956eef 100644
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -4785,11 +4785,10 @@ _bfd_x86_elf_link_setup_gnu_properties
 			    | SEC_HAS_CONTENTS | SEC_IN_MEMORY
 			    | SEC_LINKER_CREATED);
 
-	  sec = bfd_make_section_anyway_with_flags (dynobj,
-						    ".sframe",
-						    flags);
+	  sec = bfd_make_section_anyway_with_flags (dynobj, ".sframe", flags);
 	  if (sec == NULL)
 	    info->callbacks->fatal (_("%P: failed to create PLT .sframe section\n"));
+	  elf_section_type (sec) = SHT_GNU_SFRAME;
 
 	  // FIXME check this
 	  // if (!bfd_set_section_alignment (sec, class_align))
@@ -4805,6 +4804,7 @@ _bfd_x86_elf_link_setup_gnu_properties
 							flags);
 	      if (sec == NULL)
 		info->callbacks->fatal (_("%P: failed to create second PLT .sframe section\n"));
+	      elf_section_type (sec) = SHT_GNU_SFRAME;
 
 	      htab->plt_second_sframe = sec;
 	    }
@@ -4817,6 +4817,7 @@ _bfd_x86_elf_link_setup_gnu_properties
 							flags);
 	      if (sec == NULL)
 		info->callbacks->fatal (_("%P: failed to create PLT GOT .sframe section\n"));
+	      elf_section_type (sec) = SHT_GNU_SFRAME;
 
 	      htab->plt_got_sframe = sec;
 	    }
diff --git a/binutils/readelf.c b/binutils/readelf.c
index 573024727f2..87615d95ac1 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -5964,6 +5964,7 @@ get_os_specific_section_type_name (Filedata * filedata, unsigned int sh_type)
     case SHT_GNU_HASH:                return "GNU_HASH";
     case SHT_GNU_LIBLIST:             return "GNU_LIBLIST";
     case SHT_GNU_OBJECT_ONLY:	      return "GNU_OBJECT_ONLY";
+    case SHT_GNU_SFRAME:              return "GNU_SFRAME";
 
     case SHT_SUNW_move:               return "SUNW_MOVE";
     case SHT_SUNW_COMDAT:             return "SUNW_COMDAT";
@@ -8367,6 +8368,7 @@ process_section_headers (Filedata * filedata)
 
 	case SHT_NOTE:
 	case SHT_PROGBITS:
+	case SHT_GNU_SFRAME:
 	  /* Having a zero sized section is not illegal according to the
 	     ELF standard, but it might be an indication that something
 	     is wrong.  So issue a warning if we are running in lint mode.  */
diff --git a/gas/NEWS b/gas/NEWS
index 56a2b88d1ea..24b3c8ace0c 100644
--- a/gas/NEWS
+++ b/gas/NEWS
@@ -8,6 +8,8 @@
   with the applicable encoding.  Setting the flag ensures compliance with the
   updated SFrame V2 specification.
 
+  ELF SFrame sections now have section type set to SHT_GNU_SFRAME.
+
 * Add .errif and .warnif directives, permitting user-controlled diagnostics
   with conditionals that are evaluated only at the end of assembly.
 
diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index 03b6c2470e7..315d08ea996 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -1163,6 +1163,15 @@ obj_elf_attach_to_group (int dummy ATTRIBUTE_UNUSED)
   elf_set_group_name (now_seg, gname);
 }
 
+/* Handle section related directives.
+
+   Note on support for SFrame sections: These are generally expected to be
+   generated by the assembler.  However, this function permits their direct
+   creation by the user.  At the moment though, we go no extra mile by adding
+   an explicit @sframe for SHT_GNU_SFRAME (using the numeric value of section
+   type should suffice); Nor do we implement any outright refusal for
+   non-supported targets via ELFOSABI-specific checks.  */
+
 void
 obj_elf_section (int push)
 {
diff --git a/gas/dw2gencfi.c b/gas/dw2gencfi.c
index 6f8d5912a36..5c63054292f 100644
--- a/gas/dw2gencfi.c
+++ b/gas/dw2gencfi.c
@@ -2611,6 +2611,7 @@ cfi_finish (void)
 				    (SEC_ALLOC | SEC_LOAD | SEC_DATA
 				     | DWARF2_EH_FRAME_READ_ONLY),
 				    alignment);
+	  elf_section_type (sframe_seg) = SHT_GNU_SFRAME;
 	  output_sframe (sframe_seg);
 	}
       else
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.d
new file mode 100644
index 00000000000..c6ddfba3256
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.d
@@ -0,0 +1,6 @@
+#as: --gsframe
+#readelf: -S
+#name: SFrame section header in readelf output
+#...
+[ 	]*\[.*\][ 	]+\.sframe[ 	]+GNU_SFRAME.*
+#...
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.s
new file mode 100644
index 00000000000..ac9c6ca2cf3
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.s
@@ -0,0 +1,3 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
index 9c5a16f255b..8a424198a88 100644
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
@@ -72,6 +72,7 @@ if  { ([istarget "x86_64-*-*"] || [istarget "aarch64*-*-*"]
     set old_ASFLAGS "$ASFLAGS"
 
     run_dump_test "cfi-sframe-common-1"
+    run_dump_test "cfi-sframe-common-1b"
     run_dump_test "cfi-sframe-common-2"
     run_dump_test "cfi-sframe-common-3"
     run_dump_test "cfi-sframe-common-4"
diff --git a/include/elf/common.h b/include/elf/common.h
index f395278b243..0d9a7b7a8a9 100644
--- a/include/elf/common.h
+++ b/include/elf/common.h
@@ -568,6 +568,7 @@
 
 #define SHT_ANDROID_RELR             0x6fffff00
 
+#define SHT_GNU_SFRAME		     0x6ffffff4	/* SFrame stack trace information.  */
 #define SHT_GNU_ATTRIBUTES           0x6ffffff5	/* Object attributes */
 #define SHT_GNU_HASH	             0x6ffffff6	/* GNU style symbol hash table */
 #define SHT_GNU_LIBLIST	             0x6ffffff7	/* List of prelink dependencies */
diff --git a/ld/NEWS b/ld/NEWS
index 2ad06e9c124..c37352b89f6 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -9,6 +9,8 @@
   sfde_func_start_address field in the SFrame section.  Relocatable SFrame
   links are now fixed.
 
+  ELF SFrame sections now have section type set to SHT_GNU_SFRAME.
+
 * On RISC-V, add new PLT formats, and GNU property merge rules for zicfiss and
   zicfilp extensions.
 
diff --git a/libsframe/doc/sframe-spec.texi b/libsframe/doc/sframe-spec.texi
index ecc333df3ae..7307789df26 100644
--- a/libsframe/doc/sframe-spec.texi
+++ b/libsframe/doc/sframe-spec.texi
@@ -77,9 +77,10 @@ Appendices
 @section Overview
 @cindex Overview
 
-The SFrame stack trace information is provided in a loaded section, known as the
-@code{.sframe} section.  When available, the @code{.sframe} section appears in
-a new segment of its own, PT_GNU_SFRAME.
+The SFrame stack trace information is provided in a loaded section, known as
+the @code{.sframe} section.  When available, the @code{.sframe} section appears
+in segment of type PT_GNU_SFRAME.  An ELF SFrame section will have the type
+SHT_GNU_SFRAME.
 
 The SFrame format is currently supported only for select ABIs, namely, AMD64,
 AAPCS64, and s390x.