gdb/riscv: Don't error when decoding a 6 or 8 byte instruction

Message ID 20190604115054.25306-1-andrew.burgess@embecosm.com
State New
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Series
  • gdb/riscv: Don't error when decoding a 6 or 8 byte instruction
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Commit Message

Andrew Burgess June 4, 2019, 11:50 a.m.
If the RISC-V prologue scanner finds a 6 or 8 byte instruction we
currently throw an internal error, which is not great for the user.

A mechanism already exists in the prologue scanner to leave
instructions marked as unknown so that we can stop the prologue scan
without raising an error, this is used for all 2 and 4 byte
instructions that are not part of the small set the prologue scanner
actually understands.

This commit changes GDB so that all 6 and 8 byte instructions are
marked as unknown, rather than causing an error.

gdb/ChangeLog:

	* riscv-tdep.c (riscv_insn::decode): Gracefully ignore
	instructions of lengths 6 or 8 bytes.

gdb/testsuite/ChangeLog:

	* gdb.arch/riscv-unwind-long-insn-6.s: New file.
	* gdb.arch/riscv-unwind-long-insn-8.s: New file.
	* gdb.arch/riscv-unwind-long-insn.c: New file.
	* gdb.arch/riscv-unwind-long-insn.exp: New file.
---
 gdb/ChangeLog                                     |  5 ++
 gdb/riscv-tdep.c                                  | 10 ++--
 gdb/testsuite/ChangeLog                           |  7 +++
 gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s | 45 +++++++++++++++++
 gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s | 45 +++++++++++++++++
 gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c   | 25 ++++++++++
 gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp | 60 +++++++++++++++++++++++
 7 files changed, 193 insertions(+), 4 deletions(-)
 create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
 create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
 create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c
 create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp

-- 
2.14.5

Comments

John Baldwin June 4, 2019, 4:36 p.m. | #1
On 6/4/19 4:50 AM, Andrew Burgess wrote:
> If the RISC-V prologue scanner finds a 6 or 8 byte instruction we

> currently throw an internal error, which is not great for the user.

> 

> A mechanism already exists in the prologue scanner to leave

> instructions marked as unknown so that we can stop the prologue scan

> without raising an error, this is used for all 2 and 4 byte

> instructions that are not part of the small set the prologue scanner

> actually understands.

> 

> This commit changes GDB so that all 6 and 8 byte instructions are

> marked as unknown, rather than causing an error.


Looks good to me.

-- 
John Baldwin
Palmer Dabbelt June 4, 2019, 11:49 p.m. | #2
On Tue, 04 Jun 2019 04:50:54 PDT (-0700), andrew.burgess@embecosm.com wrote:
> If the RISC-V prologue scanner finds a 6 or 8 byte instruction we

> currently throw an internal error, which is not great for the user.

>

> A mechanism already exists in the prologue scanner to leave

> instructions marked as unknown so that we can stop the prologue scan

> without raising an error, this is used for all 2 and 4 byte

> instructions that are not part of the small set the prologue scanner

> actually understands.

>

> This commit changes GDB so that all 6 and 8 byte instructions are

> marked as unknown, rather than causing an error.

>

> gdb/ChangeLog:

>

> 	* riscv-tdep.c (riscv_insn::decode): Gracefully ignore

> 	instructions of lengths 6 or 8 bytes.

>

> gdb/testsuite/ChangeLog:

>

> 	* gdb.arch/riscv-unwind-long-insn-6.s: New file.

> 	* gdb.arch/riscv-unwind-long-insn-8.s: New file.

> 	* gdb.arch/riscv-unwind-long-insn.c: New file.

> 	* gdb.arch/riscv-unwind-long-insn.exp: New file.

> ---

>  gdb/ChangeLog                                     |  5 ++

>  gdb/riscv-tdep.c                                  | 10 ++--

>  gdb/testsuite/ChangeLog                           |  7 +++

>  gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s | 45 +++++++++++++++++

>  gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s | 45 +++++++++++++++++

>  gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c   | 25 ++++++++++

>  gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp | 60 +++++++++++++++++++++++

>  7 files changed, 193 insertions(+), 4 deletions(-)

>  create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s

>  create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s

>  create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c

>  create mode 100644 gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp

>

> diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c

> index 3fc86ab825..bae987cf66 100644

> --- a/gdb/riscv-tdep.c

> +++ b/gdb/riscv-tdep.c

> @@ -1385,10 +1385,12 @@ riscv_insn::decode (struct gdbarch *gdbarch, CORE_ADDR pc)

>  	m_opcode = OTHER;

>      }

>    else

> -    internal_error (__FILE__, __LINE__,

> -		    _("unable to decode %d byte instructions in "

> -		      "prologue at %s"), m_length,

> -		    core_addr_to_string (pc));

> +    {

> +      /* This must be a 6 or 8 byte instruction, we don't currently decode

> +	 any of these, so just ignore it.  */

> +      gdb_assert (m_length == 6 || m_length == 8);

> +      m_opcode = OTHER;

> +    }

>  }

>

>  /* The prologue scanner.  This is currently only used for skipping the

> diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s

> new file mode 100644

> index 0000000000..b21b1e10f3

> --- /dev/null

> +++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s

> @@ -0,0 +1,45 @@

> +/* Copyright 2019 Free Software Foundation, Inc.

> +

> +   This program is free software; you can redistribute it and/or modify

> +   it under the terms of the GNU General Public License as published by

> +   the Free Software Foundation; either version 3 of the License, or

> +   (at your option) any later version.

> +

> +   This program is distributed in the hope that it will be useful,

> +   but WITHOUT ANY WARRANTY; without even the implied warranty of

> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

> +   GNU General Public License for more details.

> +

> +   You should have received a copy of the GNU General Public License

> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

> +

> +	.option nopic

> +	.text

> +

> +        .align	1

> +	.globl	bar

> +	.type	bar, @function

> +bar:

> +        tail       1f

> +	.size	bar, .-func

> +

> +	.align	1

> +	.globl	func

> +	.type	func, @function

> +func:

> +        /* A fake 6 byte instruction.  This is never executed, but the

> +	   prologue scanner will try to decode it.  These long

> +	   instructions are ISA extensions, I use .byte rather than an

> +	   actual instruction mnemonic so that the test can be compiled

> +	   with a toolchain that doesn't include any long instruction

> +	   extensions.  */

> +        .byte 0x1f, 0x00, 0x00, 0x00, 0x00, 0x00

> +1:

> +	addi	sp,sp,-16

> +	sw	s0,12(sp)

> +	addi	s0,sp,16

> +	nop

> +	lw	s0,12(sp)

> +	addi	sp,sp,16

> +	jr	ra

> +	.size	func, .-func

> diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s

> new file mode 100644

> index 0000000000..3fad07b59d

> --- /dev/null

> +++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s

> @@ -0,0 +1,45 @@

> +/* Copyright 2019 Free Software Foundation, Inc.

> +

> +   This program is free software; you can redistribute it and/or modify

> +   it under the terms of the GNU General Public License as published by

> +   the Free Software Foundation; either version 3 of the License, or

> +   (at your option) any later version.

> +

> +   This program is distributed in the hope that it will be useful,

> +   but WITHOUT ANY WARRANTY; without even the implied warranty of

> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

> +   GNU General Public License for more details.

> +

> +   You should have received a copy of the GNU General Public License

> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

> +

> +	.option nopic

> +	.text

> +

> +        .align	1

> +	.globl	bar

> +	.type	bar, @function

> +bar:

> +        tail       1f

> +	.size	bar, .-func

> +

> +	.align	1

> +	.globl	func

> +	.type	func, @function

> +func:

> +        /* A fake 8 byte instruction.  This is never executed, but the

> +	   prologue scanner will try to decode it.  These long

> +	   instructions are ISA extensions, I use .byte rather than an

> +	   actual instruction mnemonic so that the test can be compiled

> +	   with a toolchain that doesn't include any long instruction

> +	   extensions.  */

> +        .byte 0x3f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00

> +1:

> +	addi	sp,sp,-16

> +	sw	s0,12(sp)

> +	addi	s0,sp,16

> +	nop

> +	lw	s0,12(sp)

> +	addi	sp,sp,16

> +	jr	ra

> +	.size	func, .-func

> diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c

> new file mode 100644

> index 0000000000..d601e2d3d8

> --- /dev/null

> +++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c

> @@ -0,0 +1,25 @@

> +/* Copyright 2019 Free Software Foundation, Inc.

> +

> +   This program is free software; you can redistribute it and/or modify

> +   it under the terms of the GNU General Public License as published by

> +   the Free Software Foundation; either version 3 of the License, or

> +   (at your option) any later version.

> +

> +   This program is distributed in the hope that it will be useful,

> +   but WITHOUT ANY WARRANTY; without even the implied warranty of

> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

> +   GNU General Public License for more details.

> +

> +   You should have received a copy of the GNU General Public License

> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

> +

> +extern void func (void);

> +extern void bar (void);

> +

> +int

> +main ()

> +{

> +  bar ();

> +  func ();

> +  return 0;

> +}

> diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp

> new file mode 100644

> index 0000000000..e4bc489720

> --- /dev/null

> +++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp

> @@ -0,0 +1,60 @@

> +# Copyright 2019 Free Software Foundation, Inc.

> +#

> +# This program is free software; you can redistribute it and/or modify

> +# it under the terms of the GNU General Public License as published by

> +# the Free Software Foundation; either version 3 of the License, or

> +# (at your option) any later version.

> +#

> +# This program is distributed in the hope that it will be useful,

> +# but WITHOUT ANY WARRANTY; without even the implied warranty of

> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

> +# GNU General Public License for more details.

> +#

> +# You should have received a copy of the GNU General Public License

> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.

> +

> +# This tests GDB's ability to handle 6 and 8 byte instructions in the

> +# RISC-V prologue scanner.  These instruction should be ignored, but

> +# should not result in an error that interrupts the debug session.

> +#

> +# Each of the files riscv-unwind-long-insn-*.s include a function

> +# (func) that contains a fake long instruction (6 or 8 bytes) in the

> +# prologue.  We trick GDB into parsing the fake instruction by tail

> +# calling from a different function, 'bar' to the middle of 'func'.

> +

> +if {![istarget "riscv*-*-*"]} {

> +    verbose "Skipping ${gdb_test_file_name}."

> +    return

> +}

> +

> +foreach_with_prefix {insn_size} {6 8} {

> +    standard_testfile riscv-unwind-long-insn.c \

> +	riscv-unwind-long-insn-${insn_size}.s

> +

> +    if {[prepare_for_testing "failed to prepare" $testfile \

> +	     "$srcfile $srcfile2"  debug]} {

> +	return -1

> +    }

> +

> +    if ![runto_main] then {

> +	fail "can't run to main"

> +	return 0

> +    }

> +

> +    gdb_breakpoint "bar"

> +    gdb_continue_to_breakpoint "bar"

> +

> +    # This next single instruction step takes us through a tail-call

> +    # from 'bar' into 'func'.

> +    gdb_test "si" "func \(\).*"

> +

> +    # Now check that we have a sane backtrace.

> +    gdb_test "bt" \

> +	[multi_line \

> +	     "#0\[ \t\]*func \\\(\\\) at .*$srcfile2:\[0-9\]+" \

> +	     "#1\[ \t\]*$hex in main \\\(\\\) at .*$srcfile:\[0-9\]+"] \

> +	"Backtrace to the main frame"

> +

> +    # Finally finish, and we should end up back in main.

> +    gdb_test "finish" "main \\\(\\\) at .*$srcfile:.*"

> +}


Thanks!
Andrew Burgess June 5, 2019, 9:08 a.m. | #3
* Andrew Burgess <andrew.burgess@embecosm.com> [2019-06-04 12:50:54 +0100]:

> If the RISC-V prologue scanner finds a 6 or 8 byte instruction we

> currently throw an internal error, which is not great for the user.

> 

> A mechanism already exists in the prologue scanner to leave

> instructions marked as unknown so that we can stop the prologue scan

> without raising an error, this is used for all 2 and 4 byte

> instructions that are not part of the small set the prologue scanner

> actually understands.

> 

> This commit changes GDB so that all 6 and 8 byte instructions are

> marked as unknown, rather than causing an error.

> 

> gdb/ChangeLog:

> 

> 	* riscv-tdep.c (riscv_insn::decode): Gracefully ignore

> 	instructions of lengths 6 or 8 bytes.

> 

> gdb/testsuite/ChangeLog:

> 

> 	* gdb.arch/riscv-unwind-long-insn-6.s: New file.

> 	* gdb.arch/riscv-unwind-long-insn-8.s: New file.

> 	* gdb.arch/riscv-unwind-long-insn.c: New file.

> 	* gdb.arch/riscv-unwind-long-insn.exp: New file.


I have now pushed the patch version below.  The only change from the
previous version is in riscv-unwind-long-insn.exp where I make the
test binary name unique over the two iterations of the test.

Thanks,
Andrew

--

commit 312617a3d06b8df67b9f4f63f92ebfaa6b591921
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Tue Jun 4 10:30:41 2019 +0100

    gdb/riscv: Don't error when decoding a 6 or 8 byte instruction
    
    If the RISC-V prologue scanner finds a 6 or 8 byte instruction we
    currently throw an internal error, which is not great for the user.
    
    A mechanism already exists in the prologue scanner to leave
    instructions marked as unknown so that we can stop the prologue scan
    without raising an error, this is used for all 2 and 4 byte
    instructions that are not part of the small set the prologue scanner
    actually understands.
    
    This commit changes GDB so that all 6 and 8 byte instructions are
    marked as unknown, rather than causing an error.
    
    gdb/ChangeLog:
    
            * riscv-tdep.c (riscv_insn::decode): Gracefully ignore
            instructions of lengths 6 or 8 bytes.
    
    gdb/testsuite/ChangeLog:
    
            * gdb.arch/riscv-unwind-long-insn-6.s: New file.
            * gdb.arch/riscv-unwind-long-insn-8.s: New file.
            * gdb.arch/riscv-unwind-long-insn.c: New file.
            * gdb.arch/riscv-unwind-long-insn.exp: New file.

diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index 3fc86ab825..bae987cf66 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -1385,10 +1385,12 @@ riscv_insn::decode (struct gdbarch *gdbarch, CORE_ADDR pc)
 	m_opcode = OTHER;
     }
   else
-    internal_error (__FILE__, __LINE__,
-		    _("unable to decode %d byte instructions in "
-		      "prologue at %s"), m_length,
-		    core_addr_to_string (pc));
+    {
+      /* This must be a 6 or 8 byte instruction, we don't currently decode
+	 any of these, so just ignore it.  */
+      gdb_assert (m_length == 6 || m_length == 8);
+      m_opcode = OTHER;
+    }
 }
 
 /* The prologue scanner.  This is currently only used for skipping the
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
new file mode 100644
index 0000000000..b21b1e10f3
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
@@ -0,0 +1,45 @@
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+	.option nopic
+	.text
+
+        .align	1
+	.globl	bar
+	.type	bar, @function
+bar:
+        tail       1f
+	.size	bar, .-func
+
+	.align	1
+	.globl	func
+	.type	func, @function
+func:
+        /* A fake 6 byte instruction.  This is never executed, but the
+	   prologue scanner will try to decode it.  These long
+	   instructions are ISA extensions, I use .byte rather than an
+	   actual instruction mnemonic so that the test can be compiled
+	   with a toolchain that doesn't include any long instruction
+	   extensions.  */
+        .byte 0x1f, 0x00, 0x00, 0x00, 0x00, 0x00
+1:
+	addi	sp,sp,-16
+	sw	s0,12(sp)
+	addi	s0,sp,16
+	nop
+	lw	s0,12(sp)
+	addi	sp,sp,16
+	jr	ra
+	.size	func, .-func
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
new file mode 100644
index 0000000000..3fad07b59d
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
@@ -0,0 +1,45 @@
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+	.option nopic
+	.text
+
+        .align	1
+	.globl	bar
+	.type	bar, @function
+bar:
+        tail       1f
+	.size	bar, .-func
+
+	.align	1
+	.globl	func
+	.type	func, @function
+func:
+        /* A fake 8 byte instruction.  This is never executed, but the
+	   prologue scanner will try to decode it.  These long
+	   instructions are ISA extensions, I use .byte rather than an
+	   actual instruction mnemonic so that the test can be compiled
+	   with a toolchain that doesn't include any long instruction
+	   extensions.  */
+        .byte 0x3f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+1:
+	addi	sp,sp,-16
+	sw	s0,12(sp)
+	addi	s0,sp,16
+	nop
+	lw	s0,12(sp)
+	addi	sp,sp,16
+	jr	ra
+	.size	func, .-func
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c
new file mode 100644
index 0000000000..d601e2d3d8
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c
@@ -0,0 +1,25 @@
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+extern void func (void);
+extern void bar (void);
+
+int
+main ()
+{
+  bar ();
+  func ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp
new file mode 100644
index 0000000000..ddb914295c
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp
@@ -0,0 +1,61 @@
+# Copyright 2019 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This tests GDB's ability to handle 6 and 8 byte instructions in the
+# RISC-V prologue scanner.  These instruction should be ignored, but
+# should not result in an error that interrupts the debug session.
+#
+# Each of the files riscv-unwind-long-insn-*.s include a function
+# (func) that contains a fake long instruction (6 or 8 bytes) in the
+# prologue.  We trick GDB into parsing the fake instruction by tail
+# calling from a different function, 'bar' to the middle of 'func'.
+
+if {![istarget "riscv*-*-*"]} {
+    verbose "Skipping ${gdb_test_file_name}."
+    return
+}
+
+foreach_with_prefix {insn_size} {6 8} {
+    standard_testfile riscv-unwind-long-insn.c \
+	riscv-unwind-long-insn-${insn_size}.s
+
+    set testfile "${testfile}-${insn_size}"
+    if {[prepare_for_testing "failed to prepare" $testfile \
+	     "$srcfile $srcfile2"  debug]} {
+	return -1
+    }
+
+    if ![runto_main] then {
+	fail "can't run to main"
+	return 0
+    }
+
+    gdb_breakpoint "bar"
+    gdb_continue_to_breakpoint "bar"
+
+    # This next single instruction step takes us through a tail-call
+    # from 'bar' into 'func'.
+    gdb_test "si" "func \(\).*"
+
+    # Now check that we have a sane backtrace.
+    gdb_test "bt" \
+	[multi_line \
+	     "#0\[ \t\]*func \\\(\\\) at .*$srcfile2:\[0-9\]+" \
+	     "#1\[ \t\]*$hex in main \\\(\\\) at .*$srcfile:\[0-9\]+"] \
+	"Backtrace to the main frame"
+
+    # Finally finish, and we should end up back in main.
+    gdb_test "finish" "main \\\(\\\) at .*$srcfile:.*"
+}
Pedro Alves June 5, 2019, 9:12 a.m. | #4
On 6/4/19 12:50 PM, Andrew Burgess wrote:
> +	   prologue scanner will try to decode it.  These long

> +	   instructions are ISA extensions, I use .byte rather than an

> +	   actual instruction mnemonic so that the test can be compiled


Tiny nit, but please avoid "I" in comments.  Either just don't use a
pronoun, e.g.:

   Since these long instructions are ISA extensions, use .byte

or use "we" instead.

Thanks,
Pedro Alves
Andrew Burgess June 5, 2019, 9:38 a.m. | #5
* Pedro Alves <palves@redhat.com> [2019-06-05 10:12:12 +0100]:

> On 6/4/19 12:50 PM, Andrew Burgess wrote:

> > +	   prologue scanner will try to decode it.  These long

> > +	   instructions are ISA extensions, I use .byte rather than an

> > +	   actual instruction mnemonic so that the test can be compiled

> 

> Tiny nit, but please avoid "I" in comments.  Either just don't use a

> pronoun, e.g.:

> 

>    Since these long instructions are ISA extensions, use .byte

> 

> or use "we" instead.


I pushed the patch below.

Thanks,
Andrew

--

commit 0088ba596bba2e0b94139f1c2c4f5875848edbd6
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Wed Jun 5 10:33:54 2019 +0100

    gdb/testsuite: Improve comments in recently added test
    
    Remove the use of 'I' within some comments in a recently added test.
    
    gdb/testsuite/ChangeLog:
    
            * gdb.arch/riscv-unwind-long-insn-6.s: Remove use of 'I' in
            comment.
            * gdb.arch/riscv-unwind-long-insn-8.s: Likewise.

diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
index b21b1e10f32..9bbc0ca429b 100644
--- a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
@@ -29,7 +29,7 @@ bar:
 func:
         /* A fake 6 byte instruction.  This is never executed, but the
 	   prologue scanner will try to decode it.  These long
-	   instructions are ISA extensions, I use .byte rather than an
+	   instructions are ISA extensions, use .byte rather than an
 	   actual instruction mnemonic so that the test can be compiled
 	   with a toolchain that doesn't include any long instruction
 	   extensions.  */
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
index 3fad07b59dd..0bf86940a7b 100644
--- a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
@@ -29,7 +29,7 @@ bar:
 func:
         /* A fake 8 byte instruction.  This is never executed, but the
 	   prologue scanner will try to decode it.  These long
-	   instructions are ISA extensions, I use .byte rather than an
+	   instructions are ISA extensions, use .byte rather than an
 	   actual instruction mnemonic so that the test can be compiled
 	   with a toolchain that doesn't include any long instruction
 	   extensions.  */

Patch

diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index 3fc86ab825..bae987cf66 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -1385,10 +1385,12 @@  riscv_insn::decode (struct gdbarch *gdbarch, CORE_ADDR pc)
 	m_opcode = OTHER;
     }
   else
-    internal_error (__FILE__, __LINE__,
-		    _("unable to decode %d byte instructions in "
-		      "prologue at %s"), m_length,
-		    core_addr_to_string (pc));
+    {
+      /* This must be a 6 or 8 byte instruction, we don't currently decode
+	 any of these, so just ignore it.  */
+      gdb_assert (m_length == 6 || m_length == 8);
+      m_opcode = OTHER;
+    }
 }
 
 /* The prologue scanner.  This is currently only used for skipping the
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
new file mode 100644
index 0000000000..b21b1e10f3
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-6.s
@@ -0,0 +1,45 @@ 
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+	.option nopic
+	.text
+
+        .align	1
+	.globl	bar
+	.type	bar, @function
+bar:
+        tail       1f
+	.size	bar, .-func
+
+	.align	1
+	.globl	func
+	.type	func, @function
+func:
+        /* A fake 6 byte instruction.  This is never executed, but the
+	   prologue scanner will try to decode it.  These long
+	   instructions are ISA extensions, I use .byte rather than an
+	   actual instruction mnemonic so that the test can be compiled
+	   with a toolchain that doesn't include any long instruction
+	   extensions.  */
+        .byte 0x1f, 0x00, 0x00, 0x00, 0x00, 0x00
+1:
+	addi	sp,sp,-16
+	sw	s0,12(sp)
+	addi	s0,sp,16
+	nop
+	lw	s0,12(sp)
+	addi	sp,sp,16
+	jr	ra
+	.size	func, .-func
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
new file mode 100644
index 0000000000..3fad07b59d
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn-8.s
@@ -0,0 +1,45 @@ 
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+	.option nopic
+	.text
+
+        .align	1
+	.globl	bar
+	.type	bar, @function
+bar:
+        tail       1f
+	.size	bar, .-func
+
+	.align	1
+	.globl	func
+	.type	func, @function
+func:
+        /* A fake 8 byte instruction.  This is never executed, but the
+	   prologue scanner will try to decode it.  These long
+	   instructions are ISA extensions, I use .byte rather than an
+	   actual instruction mnemonic so that the test can be compiled
+	   with a toolchain that doesn't include any long instruction
+	   extensions.  */
+        .byte 0x3f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+1:
+	addi	sp,sp,-16
+	sw	s0,12(sp)
+	addi	s0,sp,16
+	nop
+	lw	s0,12(sp)
+	addi	sp,sp,16
+	jr	ra
+	.size	func, .-func
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c
new file mode 100644
index 0000000000..d601e2d3d8
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.c
@@ -0,0 +1,25 @@ 
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+extern void func (void);
+extern void bar (void);
+
+int
+main ()
+{
+  bar ();
+  func ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp
new file mode 100644
index 0000000000..e4bc489720
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-unwind-long-insn.exp
@@ -0,0 +1,60 @@ 
+# Copyright 2019 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This tests GDB's ability to handle 6 and 8 byte instructions in the
+# RISC-V prologue scanner.  These instruction should be ignored, but
+# should not result in an error that interrupts the debug session.
+#
+# Each of the files riscv-unwind-long-insn-*.s include a function
+# (func) that contains a fake long instruction (6 or 8 bytes) in the
+# prologue.  We trick GDB into parsing the fake instruction by tail
+# calling from a different function, 'bar' to the middle of 'func'.
+
+if {![istarget "riscv*-*-*"]} {
+    verbose "Skipping ${gdb_test_file_name}."
+    return
+}
+
+foreach_with_prefix {insn_size} {6 8} {
+    standard_testfile riscv-unwind-long-insn.c \
+	riscv-unwind-long-insn-${insn_size}.s
+
+    if {[prepare_for_testing "failed to prepare" $testfile \
+	     "$srcfile $srcfile2"  debug]} {
+	return -1
+    }
+
+    if ![runto_main] then {
+	fail "can't run to main"
+	return 0
+    }
+
+    gdb_breakpoint "bar"
+    gdb_continue_to_breakpoint "bar"
+
+    # This next single instruction step takes us through a tail-call
+    # from 'bar' into 'func'.
+    gdb_test "si" "func \(\).*"
+
+    # Now check that we have a sane backtrace.
+    gdb_test "bt" \
+	[multi_line \
+	     "#0\[ \t\]*func \\\(\\\) at .*$srcfile2:\[0-9\]+" \
+	     "#1\[ \t\]*$hex in main \\\(\\\) at .*$srcfile:\[0-9\]+"] \
+	"Backtrace to the main frame"
+
+    # Finally finish, and we should end up back in main.
+    gdb_test "finish" "main \\\(\\\) at .*$srcfile:.*"
+}