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simx: reject RV32 shift-immediate code points with shamt[5] set #411

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Merged
tinebp merged 1 commit into from
Sep 10, 2026
Merged

simx: reject RV32 shift-immediate code points with shamt[5] set #411

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17 changes: 16 additions & 1 deletion sim/simx/decompressor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -219,10 +219,20 @@ DecompResult rvc_decompress(uint32_t word) {
uint32_t subfunct = bits(h, 11, 10);
if (subfunct == 0b00) { // C.SRLI
uint32_t rd_ = rcp(bits(h,9,7));
#ifndef VX_CFG_XLEN_64
// For XLEN=32 shamt[5] must be zero; those code points belong to
// custom extensions, not to a shift by 32 or more.
if (bit(h, 12)) { out.illegal = true; break; }
#endif
uint32_t sh = (bit(h,12)<<5) | bits(h,6,2);
out.instr32 = ENCI(sh, rd_, 0b101, rd_, 0b0010011);
} else if (subfunct == 0b01) { // C.SRAI
uint32_t rd_ = rcp(bits(h,9,7));
#ifndef VX_CFG_XLEN_64
// For XLEN=32 shamt[5] must be zero; those code points belong to
// custom extensions, not to a shift by 32 or more.
if (bit(h, 12)) { out.illegal = true; break; }
#endif
uint32_t sh = (bit(h,12)<<5) | bits(h,6,2);
out.instr32 = ENCI(sh, rd_, 0b101, rd_, 0b0010011) | (0x40000000u);
} else if (subfunct == 0b10) { // C.ANDI
Expand Down Expand Up @@ -289,8 +299,13 @@ DecompResult rvc_decompress(uint32_t word) {
switch (funct3) {
case 0b000: { // C.SLLI
uint32_t rd = bits(h, 11, 7);
uint32_t sh = (bit(h,12)<<5) | bits(h,6,2);
if (rd == 0) { out.illegal = true; break; }
#ifndef VX_CFG_XLEN_64
// For XLEN=32 shamt[5] must be zero; those code points belong to
// custom extensions, not to a shift by 32 or more.
if (bit(h, 12)) { out.illegal = true; break; }
#endif
uint32_t sh = (bit(h,12)<<5) | bits(h,6,2);
out.instr32 = ENCI(sh, rd, 0b001, rd, 0b0010011);
break;
}
Expand Down