Re: Emulation of shld instruction doesn't work
Guillaume Thouvenin wrote: Hello, I need to emulate the shld instruction (needed when enabling invalid guest state framework). I added the code that emulates shld in kvm (see the end of this email) and I also made a test case in user/test/x86/realmode.c. I think that the code that emulated the instruction is fine but when I run kvmctl with file realmode.flat it failed. Here is the test that I added in realmode.c: Instructions that modify memory are best tested in emulator.c rather than realmode.c. diff --git a/user/test/x86/realmode.c b/user/test/x86/realmode.c index 69ded37..8533240 100644 --- a/user/test/x86/realmode.c +++ b/user/test/x86/realmode.c @@ -141,6 +141,22 @@ int regs_equal(const struct regs *r1, const struct regs *r2, int ignore) ); \ extern u8 insn_##name[], insn_##name##_end[] +void test_shld(const struct regs *inregs, struct regs *outregs) +{ + MK_INSN(shld_test, "mov $0xbe, %ebx\n\t" + "mov $0xef00, %ecx\n\t" Do the assignments in C, modifying the inregs parameter rather than in assembly. @@ -230,7 +230,8 @@ static u16 twobyte_table[256] = { /* 0x90 - 0x9F */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xA0 - 0xA7 */ - 0, 0, 0, DstMem | SrcReg | ModRM | BitOp, 0, 0, 0, 0, + 0, 0, 0, DstMem | SrcReg | ModRM | BitOp, + DstMem | SrcReg | ModRM, DstMem | SrcReg | ModRM, 0, 0, /* 0xA8 - 0xAF */ 0, 0, 0, DstMem | SrcReg | ModRM | BitOp, 0, 0, ModRM, 0, /* 0xB0 - 0xB7 */ @@ -501,6 +502,16 @@ static u16 group2_table[] = { (_type)_x; \ }) +/* + * Reflects the parity of the given argument. It is set if + * the number of ones is even. + */ +static int even_parity(uint8_t v) +{ + asm ( "test %b0,%b0; setp %b0" : "=a" (v) : "0" (v) ); + return v; +} + static inline unsigned long ad_mask(struct decode_cache *c) { return (1UL << (c->ad_bytes << 3)) - 1; @@ -1993,6 +2004,46 @@ twobyte_insn: c->src.val &= (c->dst.bytes << 3) - 1; emulate_2op_SrcV_nobyte("bt", c->src, c->dst, ctxt->eflags); break; + case 0xa4: /* shld imm8, r, r/m */ + case 0xa5: /* shld cl, r, r/m */ { + uint8_t size; + uint8_t count; + + size = c->dst.bytes << 3; + count = (c->b & 1) ? (uint8_t) c->regs[VCPU_REGS_RCX] : insn_fetch(u8, 1, c->eip); You need to fetch during the decode phase rather than the execution phase. This is probably the source of the problem. shld has three operands, so we need to add s Src2 decode set. I guess we can start with Src2One, Src2CL, and Src2Imm8 to support shld and expand it later. + + if (count == 0) /* No operation */ + break; + + if (count > size) { + printk(KERN_INFO "shld: bad parameters \n"); + break; + } The parameters aren't bad; the processor ignores excess bits. + + c->dst.orig_val = c->dst.val; + c->dst.type = OP_REG; + c->dst.val <<= count; + c->dst.val |= ((c->src.val >> (size - count)) & ((1ull << count) - 1)); + + /* Flags affected */ + ctxt->eflags &= ~(EFLG_OF|EFLG_SF|EFLG_ZF|EFLG_PF|EFLG_CF); + + /* Set CF with left bit shifted if count is 1 or greater */ + if ((c->dst.orig_val >> (size - count)) & 1) + ctxt->eflags |= EFLG_CF; + + /* For 1-bit shit, OF is set if a sign change occured, otherwise it +* is cleared. For shift greater than 1 it is undefined */ + if (((c->dst.orig_val ^ c->dst.val) >> (size - 1)) & 1) + ctxt->eflags |= EFLG_OF; + + /* SF, ZF, and PF flags are set according to the value of the result */ + ctxt->eflags |= ((c->dst.val >> (size - 1)) & 1) ? EFLG_SF : 0; + ctxt->eflags |= (c->dst.val == 0) ? EFLG_ZF : 0; + ctxt->eflags |= even_parity(c->dst.val) ? EFLG_PF : 0; + This needs to be implemented like the rest of the instructions, with the processor calculating the flags and result. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Emulation of shld instruction doesn't work
On Wed, 8 Oct 2008 14:52:45 +0200 Guillaume Thouvenin <[EMAIL PROTECTED]> wrote: > When I launch the test, I have an emulation failure that depends of the > count operand. With count == 4 (shld $4,...) I have: > > emulation failed (emulation failure) rip 1aa 04 87 06 c0 > > If count == 12 I have > > emulation failed (emulation failure) rip 1aa 0c 87 06 c0 > > and if count == 8 > > emulation failed (emulation failure) rip 1b1 1e c4 21 66 Just to be more accurate, I added trace in shld to display information and I can see that destination operand is ok, the failure occurs after test_shld(). Regards, Guillaume -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Emulation of shld instruction doesn't work
Hello, I need to emulate the shld instruction (needed when enabling invalid guest state framework). I added the code that emulates shld in kvm (see the end of this email) and I also made a test case in user/test/x86/realmode.c. I think that the code that emulated the instruction is fine but when I run kvmctl with file realmode.flat it failed. Here is the test that I added in realmode.c: diff --git a/user/test/x86/realmode.c b/user/test/x86/realmode.c index 69ded37..8533240 100644 --- a/user/test/x86/realmode.c +++ b/user/test/x86/realmode.c @@ -141,6 +141,22 @@ int regs_equal(const struct regs *r1, const struct regs *r2, int ignore) ); \ extern u8 insn_##name[], insn_##name##_end[] +void test_shld(const struct regs *inregs, struct regs *outregs) +{ + MK_INSN(shld_test, "mov $0xbe, %ebx\n\t" + "mov $0xef00, %ecx\n\t" + "shld $8,%ecx,%ebx\n\t"); + + exec_in_big_real_mode(inregs, outregs, + insn_shld_test, + insn_shld_test_end - insn_shld_test); + + if ((outregs->ebx != 0xbeef) && (outregs->ecx != 0xef00)) + print_serial("shld: failed\n"); + else + print_serial("shld: succeded\n"); +} + void test_mov_imm(const struct regs *inregs, struct regs *outregs) { MK_INSN(mov_r32_imm_1, "mov $1234567890, %eax"); @@ -342,6 +358,7 @@ void start(void) test_call(&inregs, &outregs); test_mov_imm(&inregs, &outregs); test_cmp_imm(&inregs, &outregs); + test_shld(&inregs, &outregs); test_io(&inregs, &outregs); test_eflags_insn(&inregs, &outregs); exit(0); When I launch the test, I have an emulation failure that depends of the count operand. With count == 4 (shld $4,...) I have: emulation failed (emulation failure) rip 1aa 04 87 06 c0 If count == 12 I have emulation failed (emulation failure) rip 1aa 0c 87 06 c0 and if count == 8 emulation failed (emulation failure) rip 1b1 1e c4 21 66 If I disassemble the code of realmode.flat I can see 198: dc 21 fsubl (%ecx) ... 1aa: 66 87 06xchg %ax,(%esi) 1ad: c0 21 66shlb $0x66,(%ecx) 1b0: 87 1e xchg %ebx,(%esi) 1b2: c4 21 les(%ecx),%esp So rip values reported during the emulation failure are strange. I also notice that the problem occurs after test_shld() is called. If the test is the last one the program exit normally. I don't see what is wrong in the emulation of shld instruction so any hints are welcome. Best Regards, Guillaume diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c index a391e21..93eea5f 100644 --- a/arch/x86/kvm/x86_emulate.c +++ b/arch/x86/kvm/x86_emulate.c @@ -230,7 +230,8 @@ static u16 twobyte_table[256] = { /* 0x90 - 0x9F */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xA0 - 0xA7 */ - 0, 0, 0, DstMem | SrcReg | ModRM | BitOp, 0, 0, 0, 0, + 0, 0, 0, DstMem | SrcReg | ModRM | BitOp, + DstMem | SrcReg | ModRM, DstMem | SrcReg | ModRM, 0, 0, /* 0xA8 - 0xAF */ 0, 0, 0, DstMem | SrcReg | ModRM | BitOp, 0, 0, ModRM, 0, /* 0xB0 - 0xB7 */ @@ -501,6 +502,16 @@ static u16 group2_table[] = { (_type)_x; \ }) +/* + * Reflects the parity of the given argument. It is set if + * the number of ones is even. + */ +static int even_parity(uint8_t v) +{ + asm ( "test %b0,%b0; setp %b0" : "=a" (v) : "0" (v) ); + return v; +} + static inline unsigned long ad_mask(struct decode_cache *c) { return (1UL << (c->ad_bytes << 3)) - 1; @@ -1993,6 +2004,46 @@ twobyte_insn: c->src.val &= (c->dst.bytes << 3) - 1; emulate_2op_SrcV_nobyte("bt", c->src, c->dst, ctxt->eflags); break; + case 0xa4: /* shld imm8, r, r/m */ + case 0xa5: /* shld cl, r, r/m */ { + uint8_t size; + uint8_t count; + + size = c->dst.bytes << 3; + count = (c->b & 1) ? (uint8_t) c->regs[VCPU_REGS_RCX] : insn_fetch(u8, 1, c->eip); + + if (count == 0) /* No operation */ + break; + + if (count > size) { + printk(KERN_INFO "shld: bad parameters \n"); + break; + } + + c->dst.orig_val = c->dst.val; + c->dst.type = OP_REG; + c->dst.val <<= count; + c->dst.val |= ((c->src.val >> (size - count)) & ((1ull << count) - 1)); + + /* Flags affected */ + ctxt->eflags &= ~(EFLG_OF|EFLG_SF|EFLG_ZF|EFLG_PF|EFLG_CF); + + /* Set CF with left bit shifted if count is 1 or greater */ +