RE: [PATCH v5 00/12] Add CET shadow stack support

["Schimpe, Christina" <christina.schimpe@intel.com>]

Hi Tom,

I'll fix the issue in gdb.dap/scopes.exp described below as follows:

~~~~
save_vars { ::env(GLIBC_TUNABLES) } {

    # If x86 shadow stack is supported we need to configure GLIBC_TUNABLES
    # such that the feature is enabled and the register pl3_ssp is
    # available.  Otherwise the request to fetch all registers in this test will fail
    # with "message": "value is not available".
    if { [allow_ssp_tests] } {
	append_environment GLIBC_TUNABLES "glibc.cpu.hwcaps" "SHSTK"
    }

    if {[dap_initialize] == ""} {
	return
    }
[...}
~~~

Since to me it seems that the test
dap_check_request_and_response "fetch all registers"

requires all registers to be available.

Please let me know if you think otherwise.

Christina

> -----Original Message-----
> From: Schimpe, Christina <christina.schimpe@intel.com>
> Sent: Wednesday, August 20, 2025 11:16 AM
> To: tom@tromey.com; gdb-patches@sourceware.org
> Cc: thiago.bauermann@linaro.org; luis.machado@arm.com; Andrew
> Burgess <aburgess@redhat.com>
> Subject: RE: [PATCH v5 00/12] Add CET shadow stack support
> 
> Hi Tom,
> 
> I retested my CET shadow stack series and noticed a new fail in
> gdb.dap/scopes.exp, if  I rebase the series on latest upstream master.
> Reason seems to be the patch that you added recently: 'Do not allow DAP
> clients to dereference "void *"' and it's handling of unavailable registers.
> 
> The shadow stack feature is disabled by default, so the pl3_ssp register
> which is added with my CET shadow stack series will be shown as
> unavailable and we see a TCL error:
> ~~~
> >>> {"seq": 12, "type": "request", "command": "variables", "arguments":
> >>> {"variablesReference": 2, "count": 85}}
> Content-Length: 129^M
> ^M
> {"request_seq": 12, "type": "response", "command": "variables", "success":
> false, "message": "value is not available", "seq": 25}FAIL:
> gdb.dap/scopes.exp: fetch all registers success
> ERROR: tcl error sourcing /tmp/gdb/testsuite/gdb.dap/scopes.exp.
> ERROR: tcl error code TCL LOOKUP DICT body
> ERROR: key "body" not known in dictionary
>     while executing
> "dict get $val body variables"
>     (file "/tmp/gdb/testsuite/gdb.dap/scopes.exp" line 152)
>     invoked from within
> "source /tmp/gdb/testsuite/gdb.dap/scopes.exp"
>     ("uplevel" body line 1)
>     invoked from within
> "uplevel #0 source /tmp/gdb/testsuite/gdb.dap/scopes.exp"
>     invoked from within
> "catch "uplevel #0 source $test_file_name" msg"
> UNRESOLVED: gdb.dap/scopes.exp: testcase
> '/tmp/gdb/testsuite/gdb.dap/scopes.exp' aborted due to Tcl error ~~~
> 
> I could make this test pass by enabling the shadow stack feature in that
> specific test, if the HW supports CET shadow stack.
> The enablement would be done similar to my CET shadow stack tests:
> 
> ~~~
> save_vars { ::env(GLIBC_TUNABLES) } {
> 
>     append_environment GLIBC_TUNABLES "glibc.cpu.hwcaps" "SHSTK"
> ~~~
> 
> An alternative would be that the test is able to handle unavailable registers,
> which I think is better actually.
> But I don't have a proper fix available yet.
> 
> What do you think ?
> 
> Thanks,
> Christina
> 
> 
> 
> > -----Original Message-----
> > From: Christina Schimpe <christina.schimpe@intel.com>
> > Sent: Saturday, June 28, 2025 10:28 AM
> > To: gdb-patches@sourceware.org
> > Cc: thiago.bauermann@linaro.org; luis.machado@arm.com
> > Subject: [PATCH v5 00/12] Add CET shadow stack support
> >
> > Hi all,
> >
> > this is my v5 of the series to add amd64 shadow stack support to GDB
> > on linux.
> > It addresses the feedback of Luis.
> >
> > v4 can be found here:
> > https://sourceware.org/pipermail/gdb-patches/2025-June/218744.html
> >
> > Changes since v4:
> > - Improve some comments.
> > - Change the test in "gdb: amd64 linux coredump support with shadow
> >   stack." to also test core file generated by the linux kernel.  This
> >   requires changes for the core_find procedure to save program output,
> >   that have been implemented by Thiago already, so we include this part
> >   of the patch in this series: "gdb, testsuite: Extend core_find procedure
> >   to save program output.".  The test is now very similar to the test
> >   implemented for Guarded Control Stack corefiles.  Thanks to Thiago for
> >   providing the input here!
> >
> > I am looking forward to your feedback!
> >
> > Regards,
> >
> > Christina
> >
> > Christina Schimpe (12):
> >   gdb, testsuite: Extend core_find procedure to save program output.
> >   gdbserver: Add optional runtime register set type.
> >   gdbserver: Add assert in x86_linux_read_description.
> >   gdb: Sync up x86-gcc-cpuid.h with cpuid.h from gcc 14 branch.
> >   gdb, gdbserver: Use xstate_bv for target description creation on x86.
> >   gdb, gdbserver: Add support of Intel shadow stack pointer register.
> >   gdb: amd64 linux coredump support with shadow stack.
> >   gdb: Handle shadow stack pointer register unwinding for amd64 linux.
> >   gdb, gdbarch: Enable inferior calls for shadow stack support.
> >   gdb: Implement amd64 linux shadow stack support for inferior calls.
> >   gdb, gdbarch: Introduce gdbarch method to get the shadow stack
> >     pointer.
> >   gdb: Enable displaced stepping with shadow stack on amd64 linux.
> >
> >  gdb/NEWS                                      |   6 +
> >  gdb/amd64-linux-nat.c                         |  17 ++
> >  gdb/amd64-linux-tdep.c                        | 218 +++++++++++++++++-
> >  gdb/amd64-tdep.c                              |  35 ++-
> >  gdb/amd64-tdep.h                              |   9 +-
> >  gdb/arch-utils.c                              |  10 +
> >  gdb/arch-utils.h                              |   5 +
> >  gdb/arch/amd64-linux-tdesc.c                  |  33 +--
> >  gdb/arch/amd64-linux-tdesc.h                  |   7 +-
> >  gdb/arch/amd64.c                              |  25 +-
> >  gdb/arch/amd64.h                              |  10 +-
> >  gdb/arch/i386-linux-tdesc.c                   |  29 +--
> >  gdb/arch/i386-linux-tdesc.h                   |   5 +-
> >  gdb/arch/i386.c                               |  19 +-
> >  gdb/arch/i386.h                               |   8 +-
> >  gdb/arch/x86-linux-tdesc-features.c           |  60 ++---
> >  gdb/arch/x86-linux-tdesc-features.h           |  25 +-
> >  gdb/doc/gdb.texinfo                           |  42 ++++
> >  gdb/features/Makefile                         |   2 +
> >  gdb/features/i386/32bit-ssp.c                 |  14 ++
> >  gdb/features/i386/32bit-ssp.xml               |  11 +
> >  gdb/features/i386/64bit-ssp.c                 |  14 ++
> >  gdb/features/i386/64bit-ssp.xml               |  11 +
> >  gdb/gdbarch-gen.c                             |  54 +++++
> >  gdb/gdbarch-gen.h                             |  24 ++
> >  gdb/gdbarch_components.py                     |  31 +++
> >  gdb/i386-tdep.c                               |  51 +++-
> >  gdb/i386-tdep.h                               |  11 +-
> >  gdb/infcall.c                                 |  14 +-
> >  gdb/linux-tdep.c                              |  47 ++++
> >  gdb/linux-tdep.h                              |   7 +
> >  gdb/nat/x86-gcc-cpuid.h                       | 153 +++++++++---
> >  gdb/nat/x86-linux-tdesc.c                     |  20 +-
> >  gdb/nat/x86-linux-tdesc.h                     |   7 +-
> >  gdb/nat/x86-linux.c                           |  57 +++++
> >  gdb/nat/x86-linux.h                           |   4 +
> >  .../gdb.arch/amd64-shadow-stack-cmds.exp      | 141 +++++++++++
> >  .../gdb.arch/amd64-shadow-stack-corefile.c    |  42 ++++
> >  .../gdb.arch/amd64-shadow-stack-corefile.exp  | 110 +++++++++
> > .../gdb.arch/amd64-shadow-stack-disp-step.exp |  92 ++++++++
> >  gdb/testsuite/gdb.arch/amd64-shadow-stack.c   |  35 +++
> >  gdb/testsuite/gdb.arch/amd64-ssp.exp          |  50 ++++
> >  .../gdb.base/inline-frame-cycle-unwind.py     |   4 +
> >  gdb/testsuite/lib/gdb.exp                     |  80 ++++++-
> >  gdb/x86-linux-nat.c                           |  50 +++-
> >  gdb/x86-linux-nat.h                           |  11 +
> >  gdb/x86-tdep.c                                |  21 ++
> >  gdb/x86-tdep.h                                |   9 +
> >  gdbserver/i387-fp.cc                          |  40 ++--
> >  gdbserver/linux-amd64-ipa.cc                  |  10 +-
> >  gdbserver/linux-i386-ipa.cc                   |   6 +-
> >  gdbserver/linux-low.cc                        |  50 ++--
> >  gdbserver/linux-low.h                         |   7 +-
> >  gdbserver/linux-x86-low.cc                    |  44 +++-
> >  gdbsupport/x86-xstate.h                       |   7 +-
> >  55 files changed, 1687 insertions(+), 217 deletions(-)  create mode
> > 100644 gdb/features/i386/32bit-ssp.c  create mode 100644
> > gdb/features/i386/32bit-ssp.xml  create mode 100644
> > gdb/features/i386/64bit-ssp.c  create mode 100644
> > gdb/features/i386/64bit-ssp.xml  create mode 100644
> > gdb/testsuite/gdb.arch/amd64-shadow-stack-cmds.exp
> >  create mode 100644 gdb/testsuite/gdb.arch/amd64-shadow-stack-
> > corefile.c
> >  create mode 100644 gdb/testsuite/gdb.arch/amd64-shadow-stack-
> > corefile.exp
> >  create mode 100644 gdb/testsuite/gdb.arch/amd64-shadow-stack-disp-
> > step.exp
> >  create mode 100644 gdb/testsuite/gdb.arch/amd64-shadow-stack.c
> >  create mode 100644 gdb/testsuite/gdb.arch/amd64-ssp.exp
> >
> > --
> > 2.43.0
> 
> Intel Deutschland GmbH
> Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
> Tel: +49 89 99 8853-0, www.intel.de
> Managing Directors: Sean Fennelly, Jeffrey Schneiderman, Tiffany Doon Silva
> Chairperson of the Supervisory Board: Nicole Lau Registered Office: Munich
> Commercial Register: Amtsgericht Muenchen HRB 186928

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de
Managing Directors: Sean Fennelly, Jeffrey Schneiderman, Tiffany Doon Silva
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928