diff mbox

gdb/riscv: Remove redundant code, and catch more errors when accessing MISA

Message ID 20181026071657.GP2929@embecosm.com
State New
Headers show

Commit Message

Andrew Burgess Oct. 26, 2018, 7:16 a.m. UTC
Thanks for the reviews.

I ended up pushing the patch version below.  With some additional
testing I realised that I was always reading both locations for the
MISA register.  The problem turned out to be that `break;` within a
TRY { ... } block doesn't work (the TRY macro adds a do { ... } while
(0) block).

The new patch moves the early loop termination out of the TRY block.

Thanks,
Andrew

--

[PATCH] gdb/riscv: Remove redundant code, and catch more errors when accessing MISA

When reading the MISA register, the RISC-V specification says that, if
MISA can't be found then a default value of 0 should be assumed.

As such, this patch ensures that GDB ignores errors when accessing
both the new and old locations for the MISA register.

Additionally, this patch removes an unneeded flag parameter which
didn't provide any additional functionality beyond checking the MISA
for the default value of 0.

gdb/ChangeLog:

	* riscv-tdep.c (riscv_read_misa_reg): Update comment, remove
	READ_P parameter, catch and ignore register access errors from
	either the old or new MISA location.
	(riscv_has_feature): Update call to riscv_read_misa_reg.
---
 gdb/ChangeLog    |  7 +++++++
 gdb/riscv-tdep.c | 51 +++++++++++++++++++++++++++++----------------------
 2 files changed, 36 insertions(+), 22 deletions(-)
diff mbox

Patch

diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index f02420dfe52..e4b35a01ffc 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -290,34 +290,44 @@  static unsigned int riscv_debug_infcall = 0;
 
 static unsigned int riscv_debug_unwinder = 0;
 
-/* Read the MISA register from the target.  The register will only be read
-   once, and the value read will be cached.  If the register can't be read
-   from the target then a default value (0) will be returned.  If the
-   pointer READ_P is not null, then the bool pointed to is updated  to
-   indicate if the value returned was read from the target (true) or is the
-   default (false).  */
+/* Read the MISA register from the target.  There are a couple of locations
+   that the register might be found, these are all tried.  If the MISA
+   register can't be found at all then the default value of 0 is returned,
+   this is inline with the RISC-V specification.  */
 
 static uint32_t
-riscv_read_misa_reg (bool *read_p)
+riscv_read_misa_reg ()
 {
   uint32_t value = 0;
 
   if (target_has_registers)
     {
+      /* Old cores might have MISA located at a different offset.  */
+      static int misa_regs[] =
+	{ RISCV_CSR_MISA_REGNUM, RISCV_CSR_LEGACY_MISA_REGNUM };
+
       struct frame_info *frame = get_current_frame ();
 
-      TRY
-	{
-	  value = get_frame_register_unsigned (frame,
-					       RISCV_CSR_MISA_REGNUM);
-	}
-      CATCH (ex, RETURN_MASK_ERROR)
+      for (int i = 0; i < ARRAY_SIZE (misa_regs); ++i)
 	{
-	  /* Old cores might have MISA located at a different offset.  */
-	  value = get_frame_register_unsigned (frame,
-					       RISCV_CSR_LEGACY_MISA_REGNUM);
+	  bool success = false;
+
+	  TRY
+	    {
+	      value = get_frame_register_unsigned (frame, misa_regs[i]);
+	      success = true;
+	    }
+	  CATCH (ex, RETURN_MASK_ERROR)
+	    {
+	      /* Ignore errors, it is acceptable for a target to not
+		 provide a MISA register, in which case the default value
+		 of 0 should be used.  */
+	    }
+	  END_CATCH
+
+	  if (success)
+	    break;
 	}
-      END_CATCH
     }
 
   return value;
@@ -330,13 +340,10 @@  riscv_read_misa_reg (bool *read_p)
 static bool
 riscv_has_feature (struct gdbarch *gdbarch, char feature)
 {
-  bool have_read_misa = false;
-  uint32_t misa;
-
   gdb_assert (feature >= 'A' && feature <= 'Z');
 
-  misa = riscv_read_misa_reg (&have_read_misa);
-  if (!have_read_misa || misa == 0)
+  uint32_t misa = riscv_read_misa_reg ();
+  if (misa == 0)
     misa = gdbarch_tdep (gdbarch)->core_features;
 
   return (misa & (1 << (feature - 'A'))) != 0;