[PATCH v3 4/8] gdbserver/linux-aarch64: When thread stops, update its target description

Thiago Jung Bauermann via Gdb-patches
2023-01-30T04:46:36Z

This change prepares gdbserver to support remotely debugging programs in
aarch64-linux where different threads have different SVE vector lengths.
It allows gdbserver to support different inferior threads having different
target descriptions.

To that end, a tdesc field is added to struct thread_info. If it's
nullptr (the default) it means that the thread uses the target description
stored in struct process_info and thus gdbserver behaviour is unchanged.
The get_thread_tdesc method is added to the linux_process_target class to
allow aarch64-linux code to probe the inferior's vq register and provide a
thread-specific target description reflecting the new vector length.

After this change, all targets except SVE-supporting aarch64-linux will
still use per-process target descriptions.

Reviewed-by: Luis Machado <luis.machado@arm.com>
---
gdbserver/gdbthread.h | 4 ++++
gdbserver/linux-aarch64-low.cc | 31 +++++++++++++++++++++++++++++++
gdbserver/linux-low.cc | 17 +++++++++++++++++
gdbserver/linux-low.h | 6 ++++++
gdbserver/regcache.cc | 10 ++++++----
gdbserver/regcache.h | 4 ++++
gdbserver/tdesc.cc | 13 ++++++++++++-
gdbserver/tdesc.h | 5 +++++
8 files changed, 85 insertions(+), 5 deletions(-)

diff --git a/gdbserver/gdbthread.h b/gdbserver/gdbthread.h
index 493e1dbf6cb6..5b5ba6f8e521 100644
--- a/gdbserver/gdbthread.h
+++ b/gdbserver/gdbthread.h
@@ -80,6 +80,10 @@ struct thread_info

/* Branch trace target information for this thread. */
struct btrace_target_info *btrace = nullptr;
+
+ /* Target description for this thread. Only present if it's different
+ from the one in process_info. */
+ const struct target_desc *tdesc = nullptr;
};

extern std::list<thread_info *> all_threads;
diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
index 92c621e5548c..69765ee90db3 100644
--- a/gdbserver/linux-aarch64-low.cc
+++ b/gdbserver/linux-aarch64-low.cc
@@ -99,6 +99,9 @@ protected:

void low_arch_setup () override;

+ const struct target_desc *
+ get_thread_tdesc (const thread_info *thread) override;
+
bool low_cannot_fetch_register (int regno) override;

bool low_cannot_store_register (int regno) override;
@@ -184,6 +187,9 @@ struct arch_process_info
same for each thread, it is reasonable for the data to live here.
*/
struct aarch64_debug_reg_state debug_reg_state;
+
+ /* Whether this process has the Scalable Vector Extension available. */
+ bool has_sve;
};

/* Return true if the size of register 0 is 8 byte. */
@@ -869,6 +875,9 @@ aarch64_target::low_arch_setup ()

current_process ()->tdesc = aarch64_linux_read_description (features);

+ if (features.vq > 0)
+ current_process ()->priv->arch_private->has_sve = true;
+
/* Adjust the register sets we should use for this particular set of
features. */
aarch64_adjust_register_sets (features);
@@ -879,6 +888,28 @@ aarch64_target::low_arch_setup ()
aarch64_linux_get_debug_reg_capacity (lwpid_of (current_thread));
}

+/* Implementation of linux target ops method "get_thread_tdesc". */
+
+const struct target_desc *
+aarch64_target::get_thread_tdesc (const thread_info *thread)
+{
+ const struct process_info *process = get_thread_process (thread);
+
+ /* Only inferiors with SVE need a thread-specific target description. */
+ if (!process->priv->arch_private->has_sve)
+ return nullptr;
+
+ const struct aarch64_features features = aarch64_get_arch_features (thread);
+ const struct target_desc *tdesc = aarch64_linux_read_description (features);
+
+ /* If the target description we just found is the same as the process-wide
+ one, there's no need to set a thread-specific one. */
+ if (tdesc == process->tdesc)
+ return nullptr;
+
+ return tdesc;
+}
+
/* Implementation of linux target ops method "get_regs_info". */

const regs_info *
diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index 5cd22824e470..47916009ebaf 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -483,6 +483,12 @@ linux_process_target::arch_setup_thread (thread_info *thread)
low_arch_setup ();
}

+const struct target_desc *
+linux_process_target::get_thread_tdesc (const thread_info *thread)
+{
+ return nullptr;
+}
+
int
linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
int wstat)
@@ -2348,6 +2354,17 @@ linux_process_target::filter_event (int lwpid, int wstat)
return;
}
}
+ else
+ {
+ /* Give the arch code an opportunity to set the thread's target
+ description. */
+ const struct target_desc *new_tdesc = get_thread_tdesc (thread);
+ if (new_tdesc != thread->tdesc)
+ {
+ free_register_cache_thread (thread);
+ thread->tdesc = new_tdesc;
+ }
+ }
}

if (WIFSTOPPED (wstat) && child->must_set_ptrace_flags)
diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
index 221de85aa2ee..b52eb23cc444 100644
--- a/gdbserver/linux-low.h
+++ b/gdbserver/linux-low.h
@@ -604,6 +604,12 @@ class linux_process_target : public process_stratum_target
/* Architecture-specific setup for the current thread. */
virtual void low_arch_setup () = 0;

+ /* Allows arch-specific code to set the thread's target description when the
+ inferior stops. Returns nullptr if no thread-specific target description
+ is necessary. */
+ virtual const struct target_desc *
+ get_thread_tdesc (const thread_info *thread);
+
/* Return false if we can fetch/store the register, true if we cannot
fetch/store the register. */
virtual bool low_cannot_fetch_register (int regno) = 0;
diff --git a/gdbserver/regcache.cc b/gdbserver/regcache.cc
index 7b896a19767d..fb60e2c9c399 100644
--- a/gdbserver/regcache.cc
+++ b/gdbserver/regcache.cc
@@ -39,11 +39,11 @@ get_thread_regcache (struct thread_info *thread, int fetch)
have. */
if (regcache == NULL)
{
- struct process_info *proc = get_thread_process (thread);
+ const target_desc *tdesc = get_thread_target_desc (thread);

- gdb_assert (proc->tdesc != NULL);
+ gdb_assert (tdesc != nullptr);

- regcache = new_register_cache (proc->tdesc);
+ regcache = new_register_cache (tdesc);
set_thread_regcache_data (thread, regcache);
}

@@ -270,7 +270,9 @@ find_regno (const struct target_desc *tdesc, const char *name)
internal_error ("Unknown register %s requested", name);
}

-static void
+/* See regcache.h. */
+
+void
free_register_cache_thread (struct thread_info *thread)
{
struct regcache *regcache = thread_regcache_data (thread);
diff --git a/gdbserver/regcache.h b/gdbserver/regcache.h
index 7248bcf5808a..4beea0139cd6 100644
--- a/gdbserver/regcache.h
+++ b/gdbserver/regcache.h
@@ -79,6 +79,10 @@ void free_register_cache (struct regcache *regcache);

void regcache_invalidate_thread (struct thread_info *);

+/* Invalidate and release the register cache of the given THREAD. */
+
+void free_register_cache_thread (struct thread_info *thread);
+
/* Invalidate cached registers for all threads of the given process. */

void regcache_invalidate_pid (int pid);
diff --git a/gdbserver/tdesc.cc b/gdbserver/tdesc.cc
index 2c7257c458f4..e3339dde4d6c 100644
--- a/gdbserver/tdesc.cc
+++ b/gdbserver/tdesc.cc
@@ -123,13 +123,24 @@ copy_target_description (struct target_desc *dest,
dest->xmltarget = src->xmltarget;
}

+/* See tdesc.h. */
+
+const struct target_desc *
+get_thread_target_desc (const struct thread_info *thread)
+{
+ if (thread->tdesc != nullptr)
+ return thread->tdesc;
+
+ return get_thread_process (thread)->tdesc;
+}
+
const struct target_desc *
current_target_desc (void)
{
if (current_thread == NULL)
return &default_description;

- return current_process ()->tdesc;
+ return get_thread_target_desc (current_thread);
}

/* An empty structure. */
diff --git a/gdbserver/tdesc.h b/gdbserver/tdesc.h
index 7fe7d0d8eb30..71cc5b51c84e 100644
--- a/gdbserver/tdesc.h
+++ b/gdbserver/tdesc.h
@@ -88,6 +88,11 @@ void copy_target_description (struct target_desc *dest,
void init_target_desc (struct target_desc *tdesc,
const char **expedite_regs);

+/* Return the target description corresponding to the given THREAD. */
+
+const struct target_desc *
+ get_thread_target_desc (const struct thread_info *thread);
+
/* Return the current inferior's target description. Never returns
NULL. */