[PATCH v2 2/2] scripts/decodecode: Add support for RISC-V

Björn Töpel
2023-01-16T07:39:13Z

RISC-V has some GNU disassembly quirks, e.g. it requires '-D' to
properly disassemble .2byte directives similar to Arm [1]. Further,
GNU objdump groups RISC-V instruction by 2 or 4 byte chunks, instead
doing byte-for-byte.

Add the required switches, and translate from short/word to bytes when
ARCH is "riscv".

An example how to invoke decodecode for RISC-V:
$ echo 'Code: bf45 f793 1007 f7d9 50ef 37af d541 b7d9 7097 00c8 (80e7)
6140' | AFLAGS="-march=rv64imac_zicbom_zihintpause" \
ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- ./scripts/decodecode
Code: bf45 f793 1007 f7d9 50ef 37af d541 b7d9 7097 00c8 (80e7) 6140
All code
========
0: bf45 c.j 0xffffffffffffffb0
2: 1007f793 andi a5,a5,256
6: f7d9 c.bnez a5,0xffffffffffffff94
8: 37af50ef jal ra,0xf5382
c: d541 c.beqz a0,0xffffffffffffff94
e: b7d9 c.j 0xffffffffffffffd4
10: 00c87097 auipc ra,0xc87
14:* 614080e7 jalr ra,1556(ra) # 0xc87624 <-- trapping instruction

Code starting with the faulting instruction
===========================================
0: 614080e7 jalr ra,1556(ra)

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=10263

Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
---
scripts/decodecode | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/scripts/decodecode b/scripts/decodecode
index b28fd2686561..8fe71c292381 100755
--- a/scripts/decodecode
+++ b/scripts/decodecode
@@ -93,6 +93,11 @@ disas() {
${CROSS_COMPILE}strip $t.o
fi

+ if [ "$ARCH" = "riscv" ]; then
+ OBJDUMPFLAGS="-M no-aliases --section=.text -D"
+ ${CROSS_COMPILE}strip $t.o
+ fi
+
if [ $pc_sub -ne 0 ]; then
if [ $PC ]; then
adj_vma=$(( $PC - $pc_sub ))
@@ -126,8 +131,13 @@ get_substr_opcode_bytes_num()
do
substr+="$opc"

+ opcode="$substr"
+ if [ "$ARCH" = "riscv" ]; then
+ opcode=$(echo $opcode | tr ' ' '\n' | tac | tr -d '\n')
+ fi
+
# return if opcode bytes do not match @opline anymore
- if ! echo $opline | grep -q "$substr";
+ if ! echo $opline | grep -q "$opcode";
then
break
fi