bugTiny C Compiler - Bugs: bug #39341, TCC emits wrong opcode for XCHG

 
 

bug #39341: TCC emits wrong opcode for XCHG

Submitter:  None
Submitted:  Tue 25 Jun 2013 02:50:46 PM UTC
   
 
Category:  None Severity:  3 - Normal
Item Group:  None Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open
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Mon 02 May 2016 12:29:21 PM UTC, comment #1: 

will be fixed soon. Proposed patch:

    A bug description: a byte code ops must be declared before
    a word codes in i386-asm.h and x86_64-asm.h

diff --git a/i386-asm.h b/i386-asm.h
index 637568b..677519c 100644
--- a/i386-asm.h
+++ b/i386-asm.h
@@ -135,10 +135,10 @@ ALT(DEF_ASM_OP1(popw, 0x58, 0, OPC_REG | OPC_WL, OPT_REGW))
 ALT(DEF_ASM_OP1(popw, 0x8f, 0, OPC_MODRM | OPC_WL, OPT_REGW | OPT_EA))
 ALT(DEF_ASM_OP1(popw, 0x07, 0, OPC_WL, OPT_SEG))
.
-ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WL, OPT_REG, OPT_EAX))
-ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WL, OPT_EAX, OPT_REG))
 ALT(DEF_ASM_OP2(xchgb, 0x86, 0, OPC_MODRM | OPC_BWL, OPT_REG, OPT_EA | OPT_REG))
 ALT(DEF_ASM_OP2(xchgb, 0x86, 0, OPC_MODRM | OPC_BWL, OPT_EA | OPT_REG, OPT_REG))
+ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WL, OPT_REG, OPT_EAX))
+ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WL, OPT_EAX, OPT_REG))
.
 ALT(DEF_ASM_OP2(inb, 0xe4, 0, OPC_BWL, OPT_IM8, OPT_EAX))
 ALT(DEF_ASM_OP1(inb, 0xe4, 0, OPC_BWL, OPT_IM8))
diff --git a/x86_64-asm.h b/x86_64-asm.h
index df76bf0..9b01a02 100644
--- a/x86_64-asm.h
+++ b/x86_64-asm.h
@@ -124,10 +124,10 @@ ALT(DEF_ASM_OP1(popw, 0x58, 0, OPC_REG | OPC_WLQ, OPT_REGW))
 ALT(DEF_ASM_OP1(popw, 0x8f, 0, OPC_MODRM | OPC_WLQ, OPT_REGW | OPT_EA))
 ALT(DEF_ASM_OP1(popw, 0x07, 0, OPC_WLQ, OPT_SEG))
.
-ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WLQ, OPT_REG, OPT_EAX))
-ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WLQ, OPT_EAX, OPT_REG))
 ALT(DEF_ASM_OP2(xchgb, 0x86, 0, OPC_MODRM | OPC_BWLQ, OPT_REG, OPT_EA | OPT_REG))
 ALT(DEF_ASM_OP2(xchgb, 0x86, 0, OPC_MODRM | OPC_BWLQ, OPT_EA | OPT_REG, OPT_REG))
+ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WLQ, OPT_REG, OPT_EAX))
+ALT(DEF_ASM_OP2(xchgw, 0x90, 0, OPC_REG | OPC_WLQ, OPT_EAX, OPT_REG))
.
 ALT(DEF_ASM_OP2(inb, 0xe4, 0, OPC_BWL, OPT_IM8, OPT_EAX))

Sergey Korshunoff <seyko>
Tue 25 Jun 2013 02:50:46 PM UTC, original submission:  


void main() {
        int i = 0x16789;
        printf("Number:   %x\n", i);
        __asm__ __volatile__ ("xchg %%ah, %%al;" : "=a" (i) : "0" (i));
        printf("Reversed: %x\n", i);
}


The asm instruction is 0x94 which is xchg %eax,%esp (according to objdump and ollydbg). This leads to an immediate segfault!
The correct opcode would be 0x86 0xE0.

Anonymous

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

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