From ce887586b48acd02080c36d5495891116f886e8e Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Sat, 21 Apr 2018 11:51:34 -0600 Subject: Fix decoding of ARM VFP instructions -Wduplicated-cond pointed out that arm_record_vfp_data_proc_insn checks "opc1 == 0x0b" twice. I filed this a while ago as PR tdep/20362. Based on the ARM instruction manual at https://www.scss.tcd.ie/~waldroj/3d1/arm_arm.pdf, I think the instruction decoding in this function has two bugs. First, opc1 is computed as: opc1 = bits (arm_insn_r->arm_insn, 20, 23); [...] opc1 = opc1 & 0x04; This means that tests like: else if (opc1 == 0x01) can never be true. In the ARM manual, "opc1" corresponds to these bits: name bit r 20 q 21 D 22 p 23 ... where the D bit is not used for VFP instruction decoding. So, I believe this code should use ~0x04 instead. Second, VDIV is recognized by the bits "pqrs" being equal to "1000". This tranlates to opc1 == 0x08 -- not 0x0b. Note that pqrs==1001 is an undefined encoding, which is probably why opc2 is not checked here; this code doesn't seem to really deal with undefined encodings in general, so I've left that as is. I don't have an ARM machine or any reasonable way to test this. ChangeLog 2018-05-07 Tom Tromey PR tdep/20362: * arm-tdep.c (arm_record_vfp_data_proc_insn): Properly mask off D bit. Use correct value for VDIV. --- gdb/arm-tdep.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'gdb/arm-tdep.c') diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c index a188f0afcf6..382080a714b 100644 --- a/gdb/arm-tdep.c +++ b/gdb/arm-tdep.c @@ -11421,7 +11421,8 @@ arm_record_vfp_data_proc_insn (insn_decode_record *arm_insn_r) opc3 = bits (arm_insn_r->arm_insn, 6, 7); dp_op_sz = bit (arm_insn_r->arm_insn, 8); bit_d = bit (arm_insn_r->arm_insn, 22); - opc1 = opc1 & 0x04; + /* Mask off the "D" bit. */ + opc1 = opc1 & ~0x04; /* Handle VMLA, VMLS. */ if (opc1 == 0x00) @@ -11486,7 +11487,7 @@ arm_record_vfp_data_proc_insn (insn_decode_record *arm_insn_r) } } /* Handle VDIV. */ - else if (opc1 == 0x0b) + else if (opc1 == 0x08) { if (dp_op_sz) curr_insn_type = INSN_T1; -- cgit v1.2.1