[PATCH, V2 2/2] gas: elf: binutils: add new section type SHT_GNU_SFRAME
Indu Bhagat
indu.bhagat@oracle.com
Wed Jul 9 19:12:40 GMT 2025
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.
---
Notes:
The addition of SHT_GNU_SFRAME has been proposed on the gabi mailing
list. Ongoing discussion:
https://sourceware.org/pipermail/gnu-gabi/2025q3/000546.html
The commit of patch 2/2 in this series is contingent on when
the gnu-gabi addition of SHT_GNU_SFRAME is done. But sending the series
now to at least be prepared to commit these for 2.45 release if things
proceed well.
[Changes from V1]
- Merge the patch 3/3 "bfd: elf: add handling in
bfd_section_from_shdr" into current. Now we have 2 patches in
total.
[End of changes from V1]
[Changes from RFD]
- Add new ld/NEWS. Use the same message as gas/NEWS.
- Use "GNU_" prefix for emitted string for section header type.
- Updated the value of SHT_GNU_SFRAME.
- Added function level comment for obj_elf_section to indicate no
special handling being added for SFrame sections.
[End of changes from RFD]
---
bfd/elf-sframe.c | 16 ++++++++++++++--
bfd/elf.c | 1 +
bfd/elflink.c | 2 +-
bfd/elfxx-x86.c | 7 ++++---
binutils/readelf.c | 2 ++
gas/NEWS | 2 ++
gas/config/obj-elf.c | 9 +++++++++
gas/dw2gencfi.c | 1 +
.../gas/cfi-sframe/cfi-sframe-common-1b.d | 6 ++++++
.../gas/cfi-sframe/cfi-sframe-common-1b.s | 3 +++
gas/testsuite/gas/cfi-sframe/cfi-sframe.exp | 1 +
include/elf/common.h | 1 +
ld/NEWS | 2 ++
libsframe/doc/sframe-spec.texi | 7 ++++---
14 files changed, 51 insertions(+), 9 deletions(-)
create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.d
create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-common-1b.s
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 66a9a7a30df..07a1ea8f648 100644
--- a/gas/NEWS
+++ b/gas/NEWS
@@ -5,6 +5,8 @@
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 341a56a9eab..dbe48bae01a 100644
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
@@ -71,6 +71,7 @@ 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 74abb54254d..a083a059ca8 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -5,6 +5,8 @@
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 69fe873b9ec..02dfb5e36ca 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
and AAPCS64.
--
2.43.0
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