Re: [PATCH v2 3/4] arm64/ptrace: Support access to TPIDR2_EL0

On 8/15/22 14:30, Mark Brown wrote:

SME introduces an additional EL0 register, TPIDR2_EL0, intended for use by userspace as part of the SME. Provide ptrace access to it through the existing NT_ARM_TLS regset used for TPIDR_EL0 by expanding it to two registers with TPIDR2_EL0 being the second one.

Existing programs that query the size of the register set will be able to observe the increased size of the register set. Programs that assume the register set is single register will see no change. On systems that do not support SME TPIDR2_EL0 will read as 0 and writes will be ignored, support for SME should be queried via hwcaps as normal.

Signed-off-by: Mark Brown broonie@kernel.org

arch/arm64/kernel/ptrace.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 21da83187a60..82feabba3911 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -666,10 +666,18 @@ static int fpr_set(struct task_struct *target, const struct user_regset *regset, static int tls_get(struct task_struct *target, const struct user_regset *regset, struct membuf to) {

• int ret;
• if (target == current) tls_preserve_current_state();

• return membuf_store(&to, target->thread.uw.tp_value);

• ret = membuf_store(&to, target->thread.uw.tp_value);
• if (system_supports_tpidr2())

• ret = membuf_store(&to, target->thread.tpidr2_el0);
  

• else

• ret = membuf_zero(&to, sizeof(u64));
  

• return ret; }

static int tls_set(struct task_struct *target, const struct user_regset *regset, @@ -677,13 +685,20 @@ static int tls_set(struct task_struct *target, const struct user_regset *regset, const void *kbuf, const void __user *ubuf) { int ret;

• unsigned long tls = target->thread.uw.tp_value;

• unsigned long tls[2];

• ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &tls, 0, -1);

• tls[0] = target->thread.uw.tp_value;
• if (system_supports_sme())

• tls[1] = target->thread.tpidr2_el0;
  

• ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, tls, 0, count); if (ret) return ret;

• target->thread.uw.tp_value = tls;

• target->thread.uw.tp_value = tls[0];
• if (system_supports_sme())

• target->thread.tpidr2_el0 = tls[1];
  

• return ret; }

@@ -1392,7 +1407,7 @@ static const struct user_regset aarch64_regsets[] = { }, [REGSET_TLS] = { .core_note_type = NT_ARM_TLS,

• .n = 1,
  

• .n = 2,
  

  .size = sizeof(void *), .align = sizeof(void *), .regset_get = tls_get,

This looks good from GDB's perspective. I tried it with an unpatched GDB and it still works as it should.

TPIDR can be read correctly. I'll check TPIDR2 once it gets implemented.

Thanks, Luis