[LLVMdev] Possible bug in the dragonegg

[Pablo Barrio]

Hi Duncan,
>> #include<stdio.h>
>> #include<string.h>
>>
>> int main(int argc, char** argv){
>>
>> char a[8] = "aaaaaaa";
>> char b[8] = "bbbbbbb";
>>
>> char *c = (char*) malloc(sizeof(char)*(strlen(a)+strlen(b)+1));
>> memcpy(c, a, strlen(a));
>> memcpy(c + strlen(a), b, strlen(b) + 1);
>>
>> printf("a = %s, b = %s, c = %s\n", a, b, c);
>> }
>> *
>> and compiling and executing in the following way:
>>
>> $>  gcc -fplugin=~/dragonegg.so -O1 -fplugin-arg-dragonegg-enable-gcc-optzns
>> test.c -S -fplugin-arg-dragonegg-emit-ir -o test.ll
> What happens if you compile without -fplugin-arg-dragonegg-enable-gcc-optzns?
Then I can increase the string sizes up to 8 instead of 7, but anything 
above that segfaults.
> Also, what is the contents of test.ll?

For string sizes of 15 for a and b:


; ModuleID = 'test.c'
target datalayout = 
"e-p:64:64:64-S128-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-f128:128:128-n8:16:32:64"
target triple = "x86_64--linux-gnu"

module asm "\09.ident\09\22GCC: (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1 
LLVM: exported\22"

@.cst = linker_private unnamed_addr constant [15 x i8] 
c"aaaaaaaaaaaaaa\00", align 8
@.cst1 = linker_private unnamed_addr constant [15 x i8] 
c"bbbbbbbbbbbbbb\00", align 8
@.cst2 = linker_private unnamed_addr constant [24 x i8] c"a = %s, b = 
%s, c = %s\0A\00", align 8

define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable ssp {
entry:
   %memtmp = alloca [15 x i8], align 1
   %memtmp1 = alloca [15 x i8], align 1
   %0 = getelementptr inbounds [15 x i8]* %memtmp, i64 0, i64 0
   %1 = getelementptr inbounds [15 x i8]* %memtmp1, i64 0, i64 0
   call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* getelementptr 
inbounds ([15 x i8]* @.cst, i64 0, i64 0), i64 15, i32 1, i1 false)
   call void @llvm.memcpy.p0i8.p0i8.i64(i8* %1, i8* getelementptr 
inbounds ([15 x i8]* @.cst1, i64 0, i64 0), i64 15, i32 1, i1 false)
   %2 = call i64 @strlen(i8* %0) nounwind readonly
   %3 = call i64 @strlen(i8* %1) nounwind readonly
   %4 = add i64 %2, 1
   %5 = add i64 %4, %3
   %6 = call noalias i8* @malloc(i64 %5) nounwind
   %7 = call i64 @strlen(i8* %0) nounwind readonly
   %8 = call i64 @llvm.objectsize.i64(i8* %6, i1 false)
   %9 = call i8* @__memcpy_chk(i8* %6, i8* %0, i64 %7, i64 %8) nounwind
   %10 = call i64 @strlen(i8* %1) nounwind readonly
   %11 = add i64 %10, 1
   %12 = call i64 @strlen(i8* %0) nounwind readonly
   %13 = getelementptr i8* %6, i64 %12
   %14 = call i64 @llvm.objectsize.i64(i8* %13, i1 false)
   %15 = call i8* @__memcpy_chk(i8* %13, i8* %1, i64 %11, i64 %14) nounwind
   %16 = call i32 (i32, i8*, ...)* @__printf_chk(i32 1, i8* 
getelementptr inbounds ([24 x i8]* @.cst2, i64 0, i64 0), [15 x i8]* 
%memtmp, [15 x i8]* %memtmp1, i8* %6) nounwind
   ret i32 undef
}

declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, 
i64, i32, i1) nounwind

declare i64 @strlen(i8* nocapture) nounwind readonly

declare noalias i8* @malloc(i64) nounwind

declare i64 @llvm.objectsize.i64(i8*, i1) nounwind readnone

declare i8* @__memcpy_chk(i8*, i8*, i64, i64) nounwind

declare i32 @__printf_chk(i32, i8*, ...)





Please let me know if you can execute that file. Thanks!

>> $>  lli test.ll
>>
>> it segfaults. If I compile without "-S -fplugin-arg-dragonegg-emit-ir",
>> everything's fine. Also, if I add "-force-interpreter=true" as an lli parameter,
>> I get a "LLVM ERROR: Tried to execute an unknown external function: memcpy".
>> Amazingly, if I change the string sizes below 8 (e.g. char a[7], char b[7]),
>> everything works just fine!! It also works if I move a and b outside the
>> function (as a global), or if I malloc the arrays. Possibly a problem of
>> allocation of local vars in the stack?
>>
>> I also tried to link and create an assembler file so the interpreter could
>> resolve the memcpy call, but neither of them work with lli:
>>
>> $>  llvm-link -S test.ll>  test.ir
>>
>> $>  llvm-as test.ir -o test.s
>>
>> --
>> Pablo Barrio
>> Dpt. Electrical Engineering - Technical University of Madrid
>> Office C-203
>> Avda. Complutense s/n, 28040 Madrid
>> Tel. (+34) 915495700 ext. 4234
>> @:pbarrio at die.upm.es<mailto:pbarrio at die.upm.es>
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

-- 
Pablo Barrio
Dpt. Electrical Engineering - Technical University of Madrid
Office C-203
Avda. Complutense s/n, 28040 Madrid
Tel. (+34) 915495700 ext. 4234
@: pbarrio at die.upm.es