[PATCH v1 4/4] aarch64 SFrame: skip with warning new CFI directive used with pauth_lr

[Indu Bhagat]

On 11/25/24 8:28 AM, Matthieu Longo wrote:
> Today, SFrame v2 specification does not describe how to encode the
> information corresponding to the PAC signing method.
> SFrame v3 specification should hopefully specify it.
> 
> In the meantime, if the GNU assembler finds .cfi_negate_ra_state_with_pc
> and --gsframe is specified, it will output a warning to the user and
> will fail to generate the FDE entry.
> 
> A new SFrame test for .cfi_negate_ra_state_with_pc is also added to
> reflect this issue.

OK, LGTM. Thanks for the patch.

> ---
>   gas/gen-sframe.c                              | 16 ++++++++++++
>   .../gas/cfi-sframe/cfi-sframe-aarch64-4.d     | 25 +++++++++++++++++++
>   .../gas/cfi-sframe/cfi-sframe-aarch64-4.s     | 23 +++++++++++++++++
>   gas/testsuite/gas/cfi-sframe/cfi-sframe.exp   |  1 +
>   4 files changed, 65 insertions(+)
>   create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.d
>   create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.s
> 
> diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
> index be48b339609..041c4c7b83e 100644
> --- a/gas/gen-sframe.c
> +++ b/gas/gen-sframe.c
> @@ -1282,6 +1282,19 @@ sframe_xlate_do_aarch64_negate_ra_state (struct sframe_xlate_ctx *xlate_ctx,
>     return SFRAME_XLATE_OK;
>   }
>   
> +/* Translate DW_CFA_AARCH64_negate_ra_state_with_pc into SFrame context.
> +   Return SFRAME_XLATE_OK if success.  */
> +
> +static int
> +sframe_xlate_do_aarch64_negate_ra_state_with_pc (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
> +						 struct cfi_insn_data *cfi_insn ATTRIBUTE_UNUSED)
> +{
> +  as_warn (_("skipping SFrame FDE; .cfi_negate_ra_state_with_pc"));
> +  /* The used signing method should be encoded inside the FDE in SFrame v3.
> +     For now, PAuth_LR extension is not supported with SFrame.  */
> +  return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
> +}
> +
>   /* Translate DW_CFA_GNU_window_save into SFrame context.
>      DW_CFA_GNU_window_save is a DWARF Sparc extension, but is multiplexed with a
>      directive of DWARF AArch64 extension: DW_CFA_AARCH64_negate_ra_state.
> @@ -1397,6 +1410,9 @@ sframe_do_cfi_insn (struct sframe_xlate_ctx *xlate_ctx,
>       case DW_CFA_GNU_window_save:
>         err = sframe_xlate_do_gnu_window_save (xlate_ctx, cfi_insn);
>         break;
> +    case DW_CFA_AARCH64_negate_ra_state_with_pc:
> +      err = sframe_xlate_do_aarch64_negate_ra_state_with_pc (xlate_ctx, cfi_insn);
> +      break;
>       case DW_CFA_register:
>         err = sframe_xlate_do_register (xlate_ctx, cfi_insn);
>         break;
> diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.d
> new file mode 100644
> index 00000000000..c81888b0021
> --- /dev/null
> +++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.d
> @@ -0,0 +1,25 @@
> +#as: --gsframe
> +#objdump: --sframe=.sframe
> +#name: SFrame cfi_negate_ra_state_with_pc test
> +#warning: Warning: skipping SFrame FDE; \.cfi_negate_ra_state_with_pc
> +
> +## The support for .cfi_negate_ra_state_with_pc is currently pending on SFrame
> +## v3 (currently in development). The unimplemented support is reported to the
> +## user as a warning. Then the handler returns an error that will cause no
> +## creation of a SFrame FDE later (hence "Num FDEs: 0").
> +## Note: this test will be expected to fail when the support of PAuth_LR in
> +## SFrame will be added, so will have to be fixed.
> +
> +#...
> +Contents of the SFrame section .sframe:
> +
> +  Header :
> +
> +    Version: SFRAME_VERSION_2
> +    Flags: NONE
> +    Num FDEs: 0
> +    Num FREs: 0
> +
> +  Function Index :
> +
> +#pass
> diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.s
> new file mode 100644
> index 00000000000..5fec6740047
> --- /dev/null
> +++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-4.s
> @@ -0,0 +1,23 @@
> +## ARMv9.5 enhanced the existing PAuth feature with a new extensio called
> +## PAuth_LR. It aims at hardening the PAC in a signed return address. When
> +## signing the return address in LR, the PC is used as a diversifier, in
> +## addition to the SP to generate the PAC code.
> +## As for PAuth, when the pointers are mangled with PAuth_LR, the stack trace
> +## generator needs to know so it can mask off the PAC from the pointer value to
> +## recover the return address, and conversely, skip doing so if the pointers are
> +## not mangled.
> +##
> +## .cfi_negate_ra_state_with_pc CFI directive is used to convey this information.
> +##
> +## SFrame has currently no support for this. The support is expected in SFrame
> +## v3. This testcase ensures that the directive is understood, and outputs
> +## a warning to the user before failing to generate the FDE.
> +	.cfi_startproc
> +	.long 0
> +	.cfi_def_cfa_offset 16
> +	.cfi_negate_ra_state_with_pc
> +	.long 0
> +	.cfi_offset 29, -16
> +	.cfi_offset 30, -8
> +	.long 0
> +	.cfi_endproc
> diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
> index c646b109895..162c2b4573d 100644
> --- a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
> +++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
> @@ -98,5 +98,6 @@ if { [istarget "aarch64*-*-*"] && [gas_sframe_check] } then {
>       run_dump_test "cfi-sframe-aarch64-1"
>       run_dump_test "cfi-sframe-aarch64-2"
>       run_dump_test "cfi-sframe-aarch64-3"
> +    run_dump_test "cfi-sframe-aarch64-4"
>       run_dump_test "cfi-sframe-aarch64-pac-ab-key-1"
>   }