Implement lazy FPU initialization for ravenscar

Some ravenscar runtimes implement lazy FPU handling.  On these
runtimes, the FPU is only initialized when a task tries to use it.
Furthermore, the FP registers aren't automatically saved on a task
switch -- instead, the save is deferred until the new task tries to
use the FPU.  Furthermore, each task's context area has a flag
indicating whether the FPU has been initialized for this task.

This patch teaches GDB to understand this implementation.  When
fetching or storing registers, GDB now checks to see whether the live
FP registers should be used.  If not, the task's saved FP registers
will be used if the task has caused FPU initialization.

Currently only AArch64 uses this code.  bb-runtimes implements this
for ARM as well, but GDB doesn't yet have an arm-ravenscar-thread.c.

1 files changed, 8 insertions, 1 deletions

diff --git a/gdb/aarch64-ravenscar-thread.c b/gdb/aarch64-ravenscar-thread.c
index 045d022..eb7bda8 100644
--- a/gdb/aarch64-ravenscar-thread.c
+++ b/gdb/aarch64-ravenscar-thread.c
@@ -61,10 +61,17 @@ static const int aarch64_context_offsets[] =
   112,       116,
 };
 
+#define V_INIT_OFFSET 640
+
 /* The ravenscar_arch_ops vector for most Aarch64 targets.  */
 
 static struct ravenscar_arch_ops aarch64_ravenscar_ops
-     (aarch64_context_offsets);
+     (aarch64_context_offsets,
+      -1, -1,
+      V_INIT_OFFSET,
+      /* The FPU context buffer starts with the FPSR register.  */
+      aarch64_context_offsets[AARCH64_FPSR_REGNUM],
+      AARCH64_V0_REGNUM, AARCH64_FPCR_REGNUM);
 
 /* Register aarch64_ravenscar_ops in GDBARCH.  */