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arch-riscv: Fix compressed branch op offset

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There is a bug in RISC-V's compressed branch instructions where the
offsets are not stored in ImmOp's immediate field, causing incorrect
branchTarget() return values.  This patch adds a new compressed branch
op format, CBOp, which correctly stores the offset.

Change-Id: Iac6e9b091d63f3dce4717ee5a9ec31a7cbd6c377
Reviewed-on: https://gem5-review.googlesource.com/8441
Reviewed-by: Tuan Ta <qtt2@cornell.edu>
Maintainer: Alec Roelke <ar4jc@virginia.edu>
This commit is contained in:
Alec Roelke
2018-02-19 12:21:33 -05:00
parent 72f15d3b89
commit 7352324d4d
2 changed files with 22 additions and 17 deletions
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20
src/arch/riscv/isa/decoder.isa
View File

@@ -212,30 +212,16 @@ decode QUADRANT default Unknown::unknown() {
offset |= ~((int64_t)0x7FF);
NPC = PC + offset;
}}, IsIndirectControl, IsUncondControl, IsCall);
format BOp {
format CBOp {
0x6: c_beqz({{
int64_t offset = CIMM5<2:1> << 1 |
CIMM3<1:0> << 3 |
CIMM5<0:0> << 5 |
CIMM5<4:3> << 6;
if (CIMM3<2:2> > 0)
offset |= ~((int64_t)0xFF);
if (Rp1 == 0)
NPC = PC + offset;
NPC = PC + imm;
else
NPC = NPC;
}}, IsDirectControl, IsCondControl);
0x7: c_bnez({{
int64_t offset = CIMM5<2:1> << 1 |
CIMM3<1:0> << 3 |
CIMM5<0:0> << 5 |
CIMM5<4:3> << 6;
if (CIMM3<2:2> > 0)
offset |= ~((int64_t)0xFF);
if (Rp1 != 0)
NPC = PC + offset;
NPC = PC + imm;
else
NPC = NPC;
}}, IsDirectControl, IsCondControl);

19
src/arch/riscv/isa/formats/compressed.isa
View File

@@ -47,6 +47,25 @@ def format CIOp(imm_code, code, imm_type='int64_t', *opt_flags) {{
exec_output = ImmExecute.subst(iop)
}};
def format CBOp(code, *opt_flags) {{
imm_code = """
imm = CIMM5<2:1> << 1 |
CIMM3<1:0> << 3 |
CIMM5<0:0> << 5 |
CIMM5<4:3> << 6;
if (CIMM3<2:2> > 0)
imm |= ~((int64_t)0xFF);
"""
regs = ['_srcRegIdx[0]','_srcRegIdx[1]']
iop = InstObjParams(name, Name, 'ImmOp<int64_t>',
{'code': code, 'imm_code': imm_code,
'regs': ','.join(regs)}, opt_flags)
header_output = BranchDeclare.subst(iop)
decoder_output = ImmConstructor.subst(iop)
decode_block = BasicDecode.subst(iop)
exec_output = BranchExecute.subst(iop)
}};
def format CompressedLoad(ldisp_code, memacc_code,
ea_code, mem_flags=[], inst_flags=[]) {{
(header_output, decoder_output, decode_block, exec_output) = \