[PATCH v2 4/6] [gdb/aarch64] sme2: Core file support for ZT register set

[Luis Machado <luis.machado@arm.com>]

This patch adds support for ZT register dumps/reads for core files.  The
ZT register is available when the SME2 feature is advertised as available
by the Linux Kernel.

Unlike the enablement for SME1 and the ZA register, support for SME2 is rather
simple given the fixed size of the ZT0 register.

Validated on the Fast Models.
---
 gdb/aarch64-linux-tdep.c | 81 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 8b0b4d32971..a4d1fb87cbf 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -1374,6 +1374,50 @@ aarch64_linux_collect_za_regset (const struct regset *regset,
 			    size - SVE_HEADER_SIZE);
 }
 
+/* Supply register REGNUM from BUF to REGCACHE, using the register map
+   in REGSET.  If REGNUM is -1, do this for all registers in REGSET.
+   If BUF is NULL, set the registers to "unavailable" status.  */
+
+static void
+aarch64_linux_supply_zt_regset (const struct regset *regset,
+				struct regcache *regcache,
+				int regnum, const void *buf, size_t size)
+{
+  /* Read the ZT register note from a core file into the register buffer.  */
+
+  /* Handle an empty buffer.  */
+  if (buf == nullptr)
+    return regcache->supply_regset (regset, regnum, nullptr, size);
+
+  aarch64_gdbarch_tdep *tdep
+    = gdbarch_tdep<aarch64_gdbarch_tdep> (regcache->arch ());
+
+  /* Supply the ZT0 register contents.  */
+  regcache->raw_supply (tdep->sme2_zt0_regnum, buf);
+}
+
+/* Collect register REGNUM from REGCACHE to BUF, using the register
+   map in REGSET.  If REGNUM is -1, do this for all registers in
+   REGSET.  */
+
+static void
+aarch64_linux_collect_zt_regset (const struct regset *regset,
+				 const struct regcache *regcache,
+				 int regnum, void *buf, size_t size)
+{
+  /* Read the ZT register contents from the register buffer into the core
+     file section.  */
+
+  gdb_assert (buf != nullptr);
+
+  aarch64_gdbarch_tdep *tdep
+    = gdbarch_tdep<aarch64_gdbarch_tdep> (regcache->arch ());
+
+  /* Dump the register cache contents for the ZT register to the buffer.  */
+  regcache->collect_regset (regset, tdep->sme2_zt0_regnum, buf,
+			    AARCH64_SME2_ZT0_SIZE);
+}
+
 /* Implement the "iterate_over_regset_sections" gdbarch method.  */
 
 static void
@@ -1462,6 +1506,30 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
 	  SVE_HEADER_SIZE,
 	  SVE_HEADER_SIZE + std::pow (sve_vl_from_vq (tdep->sme_svq), 2),
 	  &aarch64_linux_za_regset, "ZA register", cb_data);
+
+      /* Handle SME2 (ZT) as well, which is only available if SME is
+	 available.  */
+      if (tdep->has_sme2 ())
+	{
+	  const struct regcache_map_entry zt_regmap[] =
+	    {
+	      { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE }
+	    };
+
+	  /* We set the register set size to REGSET_VARIABLE_SIZE here because
+	     in the future there might be more ZT registers.  */
+	  const struct regset aarch64_linux_zt_regset =
+	    {
+	      zt_regmap,
+	      aarch64_linux_supply_zt_regset, aarch64_linux_collect_zt_regset,
+	      REGSET_VARIABLE_SIZE
+	    };
+
+	  cb (".reg-aarch-zt",
+	      AARCH64_SME2_ZT0_SIZE,
+	      AARCH64_SME2_ZT0_SIZE,
+	      &aarch64_linux_zt_regset, "ZT registers", cb_data);
+	}
     }
 
   if (tdep->has_pauth ())
@@ -1567,6 +1635,19 @@ aarch64_linux_core_read_description (struct gdbarch *gdbarch,
   features.svq
     = aarch64_linux_core_read_vq (gdbarch, abfd, ".reg-aarch-za");
 
+  /* Are the ZT registers available?  */
+  if (bfd_get_section_by_name (abfd, ".reg-aarch-zt") != nullptr)
+    {
+      /* Check if ZA is also available, otherwise this is an invalid
+	 combination.  */
+      if (bfd_get_section_by_name (abfd, ".reg-aarch-za") != nullptr)
+	features.sme2 = true;
+      else
+	warning (_("While reading core file sections, found ZT registers entry "
+		   "but no ZA register entry.  The ZT contents will be "
+		   "ignored"));
+    }
+
   return aarch64_read_description (features);
 }
 
-- 
2.25.1