ld: sframe: do not generate .sframe for PLT if no .sframe is in input BFDs

GNU ld creates SFrame stack trace info for the PLT. For x86 the linker-
created .sframe section is created in setup_gnu_properties.  For s390 it
is created in create_dynamic_sections.  For both, the section data is
itself emitted a bit later in late_size_sections.  Note that for aarch64 the
linker does not create .sframe for PLT yet.

Recall that a previous patch disentangled --no-ld-generated-unwind-info
from the linker-generated .sframe sections: this means that the linker
now generates .sframe section (for .plt*) for the first input BFD
enthusiatically even when none of the input BFDs have any .sframe
section, unless --discard-sframe is also added.  The issue is that these
(unexpected) linker-generated .sframe sections (on x86_64, and s390) may
now trip the linking process, e.g., when using --orphan-handling=error
together with a linker script that treats .sframe differently than the
default linker script.
https://sourceware.org/pipermail/binutils/2026-January/147826.html

Further, with SFrame sections to be soon marked KEEP for fixing
GC/SFrame (PR ld/32769), the presence of these linker generated SFrame
sections will also cause emission of an empty .sframe (for x86_64 and
s390x), even when all input bfd's have no .sframe section.

This patch avoids creation of .sframe for .plt* if none of the input
BFDs had any .sframe section.  This then avoids creation of empty
.sframe in linked objects on x86_64 and s390x, when none of the inputs
have SFrame sections.  This also fixes PR ld/33830.

For the code changes:
Reviewed-by: Jens Remus <jremus@linux.ibm.com>

New testcases have (since the above Reviewed-by) been added.  Since
--no-ld-generated-unwind-info is not supported on aarch64, add
target-specific ld tests.  Additionally add a generic test (for all
targets that support SFrame) to ensure no output .sframe is generated if
users says no --gsframe or similar.

bfd/
	PR ld/33830
	* elf-bfd.h (_bfd_elf_sframe_present_input_bfds): New
	declaration.
	* elf-sframe.c (_bfd_elf_sframe_present_input_bfds): New
	definition.
	* elf64-s390.c (elf_s390_create_dynamic_sections): Do not
	generate .sframe for .plt unconditionally.
	* elfxx-x86.c (_bfd_x86_elf_link_setup_gnu_properties):
	Likewise.
ld/testsuite/
	PR ld/33830
	* ld-s390/no-sframe.ld: Linker script with no specification for
	SFrame sections.
	* ld-s390/s390.exp: Add new test.
	* ld-s390/sframe-command-line-2.d: New testcase that uses
	--no-ld-generated-unwind-info and a linker script that has no
	specific rules for .sframe.
	* ld-x86-64/no-sframe.ld: Likewise for x86_64.
	* ld-x86-64/sframe-command-line-2.d: Likewise for x86_64.
	* ld-x86-64/x86-64.exp: Add new test.
	* ld-sframe/no-ld-generated-sframe.d: Ensure no .sframe in
	output if no .sframe in input.
	* ld-sframe/no-sframe.ld: Linker script with no specification
	for SFrame sections.
	* ld-sframe/test.s: Add new test.

bfd/elf-bfd.h

@@ -2628,6 +2628,8 @@ extern bool _bfd_elf_maybe_strip_eh_frame_hdr
 
 extern bool _bfd_elf_sframe_present
   (struct bfd_link_info *) ATTRIBUTE_HIDDEN;
+extern bool _bfd_elf_sframe_present_input_bfds
+  (struct bfd_link_info *) ATTRIBUTE_HIDDEN;
 extern bool _bfd_elf_parse_sframe
   (bfd *, struct bfd_link_info *, asection *, struct elf_reloc_cookie *)
   ATTRIBUTE_HIDDEN;

bfd/elf-sframe.c

@@ -171,6 +171,24 @@ sframe_read_value (bfd *abfd, bfd_byte *contents, unsigned int offset,
   return value;
 }
 
+/* Return true if any of the input BFDs contains at least one .sframe
+   section.  */
+
+bool
+_bfd_elf_sframe_present_input_bfds (struct bfd_link_info *info)
+{
+  /* Find if any input file has an .sframe section.  */
+  for (bfd *pbfd = info->input_bfds; pbfd != NULL; pbfd = pbfd->link.next)
+    if (bfd_get_flavour (pbfd) == bfd_target_elf_flavour
+	&& bfd_count_sections (pbfd) != 0)
+      {
+	asection *sec = bfd_get_section_by_name (pbfd, ".sframe");
+	if (sec != NULL)
+	  return true;
+      }
+  return false;
+}
+
 /* Return true if there is at least one non-empty .sframe section in
    input files.  Can only be called after ld has mapped input to
    output sections, and before sections are stripped.  */

bfd/elf64-s390.c

@@ -4309,7 +4309,15 @@ elf_s390_create_dynamic_sections (bfd *dynobj,
         }
 
       /* Create .sframe section for .plt section.  */
-      if (!info->discard_sframe)
+      bool gen_plt_sframe_p = !info->discard_sframe
+	&& _bfd_elf_sframe_present_input_bfds (info);
+
+      /* Do not make SFrame sections for dynobj unconditionally.  If there
+	 are no SFrame sections for any input files, skip creating the linker
+	 created SFrame sections too.  Since SFrame sections are marked KEEP,
+	 prohibiting these linker-created SFrame sections when unnecessary,
+	 helps avoid creating of empty SFrame sections in the output.  */
+      if (gen_plt_sframe_p)
 	{
 	  flagword flags = (SEC_ALLOC | SEC_LOAD | SEC_READONLY
 			    | SEC_HAS_CONTENTS | SEC_IN_MEMORY

bfd/elfxx-x86.c

@@ -4827,7 +4827,16 @@ _bfd_x86_elf_link_setup_gnu_properties
 	}
 
       /* .sframe sections are emitted for AMD64 ABI only.  */
-      if (ABI_64_P (info->output_bfd) && !info->discard_sframe)
+      bool gen_plt_sframe_p = ABI_64_P (info->output_bfd)
+	&& !info->discard_sframe
+	&& _bfd_elf_sframe_present_input_bfds (info);
+
+      /* Do not make SFrame sections for dynobj unconditionally.  If there
+	 are no SFrame sections for any input files, skip creating the linker
+	 created SFrame sections too.  Since SFrame sections are marked KEEP,
+	 prohibiting these linker-created SFrame sections, when unnecessary,
+	 helps avoid creation of empty SFrame sections in the output.  */
+      if (gen_plt_sframe_p)
 	{
 	  flagword flags = (SEC_ALLOC | SEC_LOAD | SEC_READONLY
 			    | SEC_HAS_CONTENTS | SEC_IN_MEMORY

ld/testsuite/ld-s390/no-sframe.ld

@@ -0,0 +1,6 @@
+ENTRY(_start)
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+  .text : { *(.text) }
+}

ld/testsuite/ld-s390/s390.exp

@@ -192,6 +192,9 @@ if [istarget "s390x-*-*"] {
     if { ![skip_sframe_tests] } {
 	run_dump_test "sframe-simple-1"
 	run_dump_test "sframe-plt-1"
+	# Test --discard-sframe
 	run_dump_test "sframe-command-line-1"
+	# Test --no-ld-generated-unwind-info
+	run_dump_test "sframe-command-line-2"
     }
 }

ld/testsuite/ld-s390/sframe-command-line-2.d

@@ -0,0 +1,10 @@
+#as:
+#source: sframe-foo.s
+#ld: --no-ld-generated-unwind-info -T no-sframe.ld -e foo
+#objdump: -hw
+#name: No interaction between --no-ld-generated-unwind-info and SFrame
+
+#failif
+#...
+  [0-9] .sframe .*
+#...

ld/testsuite/ld-sframe/no-ld-generated-sframe.d

@@ -0,0 +1,10 @@
+#as:
+#source: test.s
+#ld: -T no-sframe.ld
+#objdump: -hw
+#name: No SFrame section in output with no --gsframe
+
+#failif
+#...
+  [0-9] .sframe .*
+#...

ld/testsuite/ld-sframe/no-sframe.ld

@@ -0,0 +1,6 @@
+ENTRY(_start)
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+  .text : { *(.text) }
+}

ld/testsuite/ld-sframe/test.s

@@ -0,0 +1,11 @@
+	.text
+	.globl	foo
+	.type	foo, @function
+foo:
+	.cfi_startproc
+	.cfi_def_cfa_offset 16
+	.cfi_endproc
+
+	.globl _start
+_start:
+	.long   foo

ld/testsuite/ld-x86-64/no-sframe.ld

@@ -0,0 +1,6 @@
+ENTRY(_start)
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+  .text : { *(.text) }
+}

ld/testsuite/ld-x86-64/sframe-command-line-2.d

@@ -0,0 +1,10 @@
+#as:
+#source: sframe-foo.s
+#ld: --no-ld-generated-unwind-info -T no-sframe.ld -e foo
+#objdump: -hw
+#name: No interaction between --no-ld-generated-unwind-info and SFrame
+
+#failif
+#...
+  [0-9] .sframe .*
+#...

ld/testsuite/ld-x86-64/x86-64.exp

@@ -588,7 +588,10 @@ run_dump_test "tls-le-pic-3-x32"
 if { ![skip_sframe_tests] } {
     run_dump_test "sframe-simple-1"
     run_dump_test "sframe-link-1"
+    # Test --discard-sframe
     run_dump_test "sframe-command-line-1"
+    # Test --no-ld-generated-unwind-info
+    run_dump_test "sframe-command-line-2"
     run_dump_test "sframe-reloc-1"
     run_dump_test "sframe-plt-1"
     run_dump_test "sframe-ibt-plt-1"