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authorMark Brown <broonie@kernel.org>2024-11-06 17:41:32 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2024-11-12 14:53:34 +0000
commitc0139f6cbb1fc6438509467ec0455a200cc49a43 (patch)
tree01f3ce3e55568ba4d621e31de9952221e48ee308 /Documentation/arch
parentf95382d73ec8bfee2b4a00b2ac4aa4530f7c4af3 (diff)
arm64/ptrace: Clarify documentation of VL configuration via ptrace
When we configure SVE, SSVE or ZA via ptrace we allow the user to configure the vector length and specify any of the flags that are accepted when configuring via prctl(). This includes the S[VM]E_SET_VL_ONEXEC flag which defers the configuration of the VL until an exec(). We don't do anything to limit the provision of register data as part of configuring the _ONEXEC VL but as a function of the VL enumeration support we do this will be interpreted using the vector length currently configured for the process. This is all a bit surprising, and probably we should just not have allowed register data to be specified with _ONEXEC, but it's our ABI so let's add some explicit documentation in both the ABI documents and the source calling out what happens. The comments are also missing the fact that since SME does not have a mandatory 128 bit VL it is possible for VL enumeration to result in the configuration of a higher VL than was requested, cover that too. Signed-off-by: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20241106-arm64-sve-ptrace-vl-set-v1-1-3b164e8b559c@kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'Documentation/arch')
-rw-r--r--Documentation/arch/arm64/sme.rst4
-rw-r--r--Documentation/arch/arm64/sve.rst4
2 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/arch/arm64/sme.rst b/Documentation/arch/arm64/sme.rst
index be317d457417..b2fa01f85cb5 100644
--- a/Documentation/arch/arm64/sme.rst
+++ b/Documentation/arch/arm64/sme.rst
@@ -346,6 +346,10 @@ The regset data starts with struct user_za_header, containing:
* Writes to NT_ARM_ZT will set PSTATE.ZA to 1.
+* If any register data is provided along with SME_PT_VL_ONEXEC then the
+ registers data will be interpreted with the current vector length, not
+ the vector length configured for use on exec.
+
8. ELF coredump extensions
---------------------------
diff --git a/Documentation/arch/arm64/sve.rst b/Documentation/arch/arm64/sve.rst
index 8d8837fc39ec..28152492c29c 100644
--- a/Documentation/arch/arm64/sve.rst
+++ b/Documentation/arch/arm64/sve.rst
@@ -402,6 +402,10 @@ The regset data starts with struct user_sve_header, containing:
streaming mode and any SETREGSET of NT_ARM_SSVE will enter streaming mode
if the target was not in streaming mode.
+* If any register data is provided along with SVE_PT_VL_ONEXEC then the
+ registers data will be interpreted with the current vector length, not
+ the vector length configured for use on exec.
+
* The effect of writing a partial, incomplete payload is unspecified.