gdb/riscv: use a single regset supply function for riscv fbsd & linux

The RISC-V x0 register is hard-coded to zero.  As such neither Linux
or FreeBSD supply the value of the register x0 in their core dump
files.

For FreeBSD we take care of this by manually supplying the value of x0
in riscv_fbsd_supply_gregset, however we don't do this for Linux.  As
a result after loading a core file on Linux we see this behaviour:

  (gdb) p $x0
  $1 = <unavailable>

In this commit I make riscv_fbsd_supply_gregset a common function that
can be shared between RISC-V for FreeBSD and Linux, this resolves the
above issue.

There is a similar problem for the two registers `fflags` and `frm`.
These two floating point related CSRs are a little weird.  They are
separate CSRs in the RISC-V specification, but are actually sub-fields
of the `fcsr` CSR.

As a result neither Linux or FreeBSD supply the `fflags` or `frm`
registers as separate fields in their core dumps, and so, after
restoring a core dump these register are similarly unavailable.

In this commit I supply `fflags` and `frm` by first asking for the
value of `fcsr`, extracting the two fields, and using these to supply
the values for `fflags` and `frm`.

gdb/ChangeLog:

	* riscv-fbsd-tdep.c (riscv_fbsd_supply_gregset): Delete.
	(riscv_fbsd_gregset): Use riscv_supply_regset.
	(riscv_fbsd_fpregset): Likewise.
	* riscv-linux-tdep.c (riscv_linux_gregset): Likewise.
	(riscv_linux_fregset): Likewise.
	* riscv-tdep.c (riscv_supply_regset): Define new function.
	* riscv-tdep.h (riscv_supply_regset): Declare new function.

1 files changed, 50 insertions, 0 deletions

diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index c0e84e5..b16e7d7 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -3786,6 +3786,56 @@ riscv_init_reggroups ()
   csr_reggroup = reggroup_new ("csr", USER_REGGROUP);
 }
 
+/* See riscv-tdep.h.  */
+
+void
+riscv_supply_regset (const struct regset *regset,
+		     struct regcache *regcache, int regnum,
+		     const void *regs, size_t len)
+{
+  regcache->supply_regset (regset, regnum, regs, len);
+
+  if (regnum == -1 || regnum == RISCV_ZERO_REGNUM)
+    regcache->raw_supply_zeroed (RISCV_ZERO_REGNUM);
+
+  if (regnum == -1 || regnum == RISCV_CSR_FFLAGS_REGNUM
+      || regnum == RISCV_CSR_FRM_REGNUM)
+    {
+      int fcsr_regnum = RISCV_CSR_FCSR_REGNUM;
+
+      /* Ensure that FCSR has been read into REGCACHE.  */
+      if (regnum != -1)
+	regcache->supply_regset (regset, fcsr_regnum, regs, len);
+
+      /* Grab the FCSR value if it is now in the regcache.  We must check
+	 the status first as, if the register was not supplied by REGSET,
+	 this call will trigger a recursive attempt to fetch the
+	 registers.  */
+      if (regcache->get_register_status (fcsr_regnum) == REG_VALID)
+	{
+	  ULONGEST fcsr_val;
+	  regcache->raw_read (fcsr_regnum, &fcsr_val);
+
+	  /* Extract the fflags and frm values.  */
+	  ULONGEST fflags_val = fcsr_val & 0x1f;
+	  ULONGEST frm_val = (fcsr_val >> 5) & 0x7;
+
+	  /* And supply these if needed.  */
+	  if (regnum == -1 || regnum == RISCV_CSR_FFLAGS_REGNUM)
+	    regcache->raw_supply_integer (RISCV_CSR_FFLAGS_REGNUM,
+					  (gdb_byte *) &fflags_val,
+					  sizeof (fflags_val),
+					  /* is_signed */ false);
+
+	  if (regnum == -1 || regnum == RISCV_CSR_FRM_REGNUM)
+	    regcache->raw_supply_integer (RISCV_CSR_FRM_REGNUM,
+					  (gdb_byte *)&frm_val,
+					  sizeof (fflags_val),
+					  /* is_signed */ false);
+	}
+    }
+}
+
 void _initialize_riscv_tdep ();
 void
 _initialize_riscv_tdep ()