[PATCH v3 00/11] s390: Support to generate .sframe in assembler and linker
Indu Bhagat
indu.bhagat@oracle.com
Sat Jul 5 23:27:41 GMT 2025
On 6/27/25 4:08 AM, Jens Remus wrote:
> Changes in v3 (see individual patch notes for further details):
> - Update "Changes from Version 1 to Version 2" in SFrame spec. (Indu)
> - Align to improvements from commit 4e94f0075669 ("libsframe: fix issue
> finding FRE in PCMASK type SFrame FDEs"). (Indu)
> - Incorporated review feedback from v2, mostly rewording commit
> messages, SFrame specification, code comments.
>
> This patch series adds support on s390x to generate SFrame stack trace
> information (.sframe section) in the assembler from CFI directives and
> in the linker for the linker-generated .plt section.
>
> Patches 1 and 2 are preparatory. Patch 1 resolves an endianness
> conversion issue in SFrame common code. Patch 2 restructures the linker
> dump tests on s390/s390x, to enable adding SFrame tests that are only
> run if SFrame is supported.
>
> Patch 3 adds initial support to generate SFrame stack trace information
> from CFI directives in the assembler on s390x. Due to differences in
> the s390x ELF ABI [1] compared to the AArch64 and x86-64 AMD64 ELF ABIs
> and the simplified assumptions of the SFrame format V2 there are a few
> limitations, that mostly get addressed by patches 4 and 5.
>
> Patches 4 and 5 address generic SFrame limitations, by introducing S390-
> specific extensions to the SFrame format. Patch 4 enables to represent
> FP/RA saved in another register (instead of on the stack), which can be
> observed in leaf functions, by encoding the DWARF register number as
> FP/RA offset. Patch 5 enables to represent FP without RA saved (on the
> stack or in another register), by using an invalid RA offset value as
> padding.
>
> Patch 6 adds support to generate SFrame stack trace information for the
> linker-generated .plt section in the linker on s390x.
>
> Patch 7 (new) adds a libsframe test for PLT0/PLTN with only one FRE
> each.
>
> Patches 8 and 9 enable and improve the use of signed 8-bit SFrame CFA,
> FP, and RA offsets on S390. Patch 8 enables the use by storing the CFA
> offset adjusted by a s390x-specific CFA adjustment of -160. Patch 9
> improves the use by additionally storing the CFA offset factorized, with
> a s390x-specific CFA offset alignment factor of 8 factored out.
>
> Patch 10 (new) adds a port of a new SFrame test on x86-64 to s390x.
>
> Patch 11 (new) completes this series by adding a Binutils NEWS entry
> announcing the s390 64-bit (s390x) support for SFrame and updating the
> GAS NEWS entry (no longer initial support).
>
> Open issues and limitations that could be addressed in SFrame, GCC, and
> Glibc:
>
> - Limitation: Potential use of non-SP/FP register as CFA base register.
> The s390x ELF ABI does not designate a dedicated frame pointer (FP)
> register. With a recent update it does designate register 11 (r11)
> as preferred FP register, which is used by GCC and Clang on s390x.
> This will most likely remain a permanent limitation, mostly affecting
> hand-written assembler code.
>
> - Issue: GCC use of non-SP/FP register as CFA base register. GCC can
> be observed to use the non-FP register r14 as temporary CFA base
> register in the stack clash protector of variadic functions. This
> could be addressed either in GCC or with the planned SFrame V3
> enhancement [2] to support non-SP/FP CFA base registers for topmost
> frames.
>
> - Issue: Glibc use of non-preferred FP register r12 as frame pointer
> in _dl_runtime_profile. I am working on Glibc patches to improve
> SFrame compatibility on s390x, which will resolve this issue.
>
> - Limitation: Glibc use of non-default RA register r0 in fentry
> used for profiling. This will most likely remain a permanent
> limitation, that the use of SFrame stack tracing, e.g. using perf,
> cannot be combined with profiling.
> Note that support for non-default RA registers for topmost frames
> could easily be implemented by representing a non-default RA register
> as default RA register saved in non-default RA register and then
> tracking the non-default RA register for the rest of that FDE.
> But this would not resolve the issue, as Glibc fentry does call
> another function using normal calling conventions. With that the
> frame with the default RA register saved in the non-default RA
> register would no longer be the topmost in the call stack. A
> SFrame stack tracer implementation can only access register contents
> in the topmost frame.
>
> [1]: s390x ELF ABI, https://github.com/IBM/s390x-abi/releases
> [2]: SFrame V3 TODOs,
> https://sourceware.org/binutils/wiki/sframe/sframev3todo
>
> Regards,
> Jens
>
(Sorry for the delay in reviewing this series, I was on time off for few
days.)
The series looks good to me overall.
Thanks
> Jens Remus (11):
> sframe: Ignore section padding when converting endianness
> s390: Explicitly list linker dump tests
> s390: Initial support to generate .sframe from CFI directives in
> assembler
> s390: Represent FP/RA saved in register in SFrame
> s390: Represent FP without RA saved in SFrame
> s390: Add SFrame stack trace information for .plt section
> libsframe: Add test for PLT0 and PLTN with only one FRE each
> s390: Store SFrame CFA offset adjusted
> s390: Store SFrame CFA offset adjusted and scaled down
> s390: sframe: Test handling of .cfi_def_cfa_register
> s390: Announce s390 64-bit (s390x) SFrame V2 support in binutils
>
> bfd/elf64-s390.c | 259 ++++++++++++++++++
> binutils/NEWS | 7 +
> gas/NEWS | 3 +
> gas/config/tc-s390.c | 55 ++++
> gas/config/tc-s390.h | 31 +++
> gas/gen-sframe.c | 99 ++++++-
> .../gas/cfi-sframe/cfi-sframe-s390x-1.d | 23 ++
> .../gas/cfi-sframe/cfi-sframe-s390x-1.s | 37 +++
> .../gas/cfi-sframe/cfi-sframe-s390x-2.d | 23 ++
> .../gas/cfi-sframe/cfi-sframe-s390x-2.s | 37 +++
> .../gas/cfi-sframe/cfi-sframe-s390x-3.d | 19 ++
> .../gas/cfi-sframe/cfi-sframe-s390x-3.s | 4 +
> .../gas/cfi-sframe/cfi-sframe-s390x-err-1.d | 15 +
> .../gas/cfi-sframe/cfi-sframe-s390x-err-1.s | 37 +++
> .../gas/cfi-sframe/cfi-sframe-s390x-err-2.d | 15 +
> .../gas/cfi-sframe/cfi-sframe-s390x-err-2.s | 37 +++
> .../gas/cfi-sframe/cfi-sframe-s390x-err-3.d | 15 +
> .../gas/cfi-sframe/cfi-sframe-s390x-err-3.s | 5 +
> .../cfi-sframe-s390x-fpra-offset-1.d | 22 ++
> .../cfi-sframe-s390x-fpra-offset-1.s | 15 +
> .../cfi-sframe-s390x-fpra-offset-2.d | 22 ++
> .../cfi-sframe-s390x-fpra-offset-2.s | 15 +
> .../cfi-sframe-s390x-fpra-register-1.d | 22 ++
> .../cfi-sframe-s390x-fpra-register-1.s | 15 +
> .../cfi-sframe-s390x-fpra-register-2.d | 22 ++
> .../cfi-sframe-s390x-fpra-register-2.s | 15 +
> gas/testsuite/gas/cfi-sframe/cfi-sframe.exp | 19 +-
> include/sframe-api.h | 12 +-
> include/sframe.h | 59 +++-
> ld/NEWS | 4 +
> ld/testsuite/ld-s390/s390.exp | 18 +-
> ld/testsuite/ld-s390/sframe-bar.s | 21 ++
> ld/testsuite/ld-s390/sframe-foo.s | 9 +
> ld/testsuite/ld-s390/sframe-plt-1.d | 28 ++
> ld/testsuite/ld-s390/sframe-simple-1.d | 31 +++
> libsframe/Makefile.in | 42 ++-
> libsframe/doc/sframe-spec.texi | 116 +++++++-
> libsframe/sframe-dump.c | 28 +-
> libsframe/sframe.c | 31 ++-
> libsframe/testsuite/libsframe.find/find.exp | 5 +
> libsframe/testsuite/libsframe.find/local.mk | 5 +
> .../testsuite/libsframe.find/plt-findfre-2.c | 192 +++++++++++++
> 42 files changed, 1443 insertions(+), 46 deletions(-)
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-1.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-1.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-2.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-2.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-3.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-3.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-err-1.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-err-1.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-err-2.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-err-2.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-err-3.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-err-3.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-1.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-1.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-1.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-1.s
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.d
> create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.s
> create mode 100644 ld/testsuite/ld-s390/sframe-bar.s
> create mode 100644 ld/testsuite/ld-s390/sframe-foo.s
> create mode 100644 ld/testsuite/ld-s390/sframe-plt-1.d
> create mode 100644 ld/testsuite/ld-s390/sframe-simple-1.d
> create mode 100644 libsframe/testsuite/libsframe.find/plt-findfre-2.c
>
More information about the Binutils
mailing list