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Zalunin Pavel

2008-Jan-06 19:52 UTC

[LLVMdev] Another memory fun

hm.... I think, that is valid in c

but next code too doesn't works right:
; ModuleID = 'sample.lz'
@.str1 = internal global [6 x i8] c"world\00"           ; <[6 x
i8]*>
[#uses=1]
@.str2 = internal global [7 x i8] c"hello \00"          ; <[7 x
i8]*>
[#uses=1]
@.str7 = internal global [7 x i8] c"father\00"          ; <[7 x
i8]*>
[#uses=1]
@.str8 = internal global [8 x i8] c"mother \00"         ; <[8 x
i8]*>
[#uses=1]

declare i32 @puts(i8*)

declare i8* @strcat(i8*, i8*)

declare i32 @strlen(i8*)

declare void @llvm.memcpy.i32(i8*, i8*, i32, i32)

define i32 @main() {
mainBlock:
        %str3 = getelementptr [7 x i8]* @.str2, i64 0, i64 0            ;
<i8*> [#uses=2]
        %str4 = getelementptr [6 x i8]* @.str1, i64 0, i64 0            ;
<i8*> [#uses=1]
        call i8* @strcat( i8* %str3, i8* %str4 )                ; <i8*>:0
[#uses=0]
        %tmp6 = call i32 @puts( i8* %str3 )             ; <i32> [#uses=0]
        %str9 = getelementptr [8 x i8]* @.str8, i64 0, i64 0            ;
<i8*> [#uses=2]
        %str10 = getelementptr [7 x i8]* @.str7, i64 0, i64 0           ;
<i8*> [#uses=1]
        call i8* @strcat( i8* %str9, i8* %str10 )               ; <i8*>:1
[#uses=0]
        %tmp12 = call i32 @puts( i8* %str9 )            ; <i32> [#uses=0]
        ret i32 0
}


writes:
%
hello world
mother orld


I tried decompile code:
 main(int argc, char **argv) {
  char str1[] = "mother ";
  strcat(str1, "father");
  return 0;
}

decompiler gives to me code, in this code string " mother\0" presents
as:

%str1 = alloca [8 x i8], align 16		; <[8 x i8]*> [#uses=9]
	%tmp1 = getelementptr [8 x i8]* %str1, i32 0, i32 0		; <i8*> [#uses=2]
	store i8 109, i8* %tmp1, align 16
	%tmp4 = getelementptr [8 x i8]* %str1, i32 0, i32 1		; <i8*> [#uses=1]
	store i8 111, i8* %tmp4, align 1
	%tmp7 = getelementptr [8 x i8]* %str1, i32 0, i32 2		; <i8*> [#uses=1]
	store i8 116, i8* %tmp7, align 1
	%tmp10 = getelementptr [8 x i8]* %str1, i32 0, i32 3		; <i8*> [#uses=1]
	store i8 104, i8* %tmp10, align 1
	%tmp13 = getelementptr [8 x i8]* %str1, i32 0, i32 4		; <i8*> [#uses=1]
	store i8 101, i8* %tmp13, align 1
	%tmp16 = getelementptr [8 x i8]* %str1, i32 0, i32 5		; <i8*> [#uses=1]
	store i8 114, i8* %tmp16, align 1
	%tmp19 = getelementptr [8 x i8]* %str1, i32 0, i32 6		; <i8*> [#uses=1]
	store i8 32, i8* %tmp19, align 1
	%tmp22 = getelementptr [8 x i8]* %str1, i32 0, i32 7		; <i8*> [#uses=1]

	store i8 0, i8* %tmp22, align 1


it's looks funny, can you say another less complex way to do this operation?
Thanks

Best regards,
    Zalunin Pavel
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Török Edwin

2008-Jan-06 20:33 UTC

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[LLVMdev] Another memory fun

Zalunin Pavel wrote:> hm.... I think, that is valid in c
> [...]
> but next code too doesn't works right:
> I tried decompile code:
>  main(int argc, char **argv) {
>   char str1[] = "mother ";
>   strcat(str1, "father");
>   return 0;
> }
>
Valid C doesn't mean only that it compiles, but also that you are
properly using library functions.
Consult the manpage for strcat(3): "the dest string  must have enough
space for the result";
in your example it doesn't have.

Best regards,
--Edwin

Syed Faraz Mahmood

2008-Jan-06 20:47 UTC

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[LLVMdev] Another memory fun

well this is invalid in c as u need to allocate enough memory to be able to
copy the 2nd string  , if not enough allocated mem is available then it will
overwrite address available, corrupting the memory. :)

regards
faraz

On Jan 6, 2008 11:52 PM, Zalunin Pavel <wr4bbit at gmail.com> wrote:
> hm.... I think, that is valid in c
>
> but next code too doesn't works right:
> ; ModuleID = 'sample.lz'
> @.str1 = internal global [6 x i8] c"world\00"           ; <[6
x i8]*>
> [#uses=1]
> @.str2 = internal global [7 x i8] c"hello \00"          ; <[7
x i8]*>
> [#uses=1]
> @.str7 = internal global [7 x i8] c"father\00"          ; <[7
x i8]*>
> [#uses=1]
> @.str8 = internal global [8 x i8] c"mother \00"         ; <[8
x i8]*>
> [#uses=1]
>
> declare i32 @puts(i8*)
>
> declare i8* @strcat(i8*, i8*)
>
> declare i32 @strlen(i8*)
>
> declare void @llvm.memcpy.i32(i8*, i8*, i32, i32)
>
> define i32 @main() {
> mainBlock:
>         %str3 = getelementptr [7 x i8]* @.str2, i64 0, i64 0            ;
> <i8*> [#uses=2]
>         %str4 = getelementptr [6 x i8]* @.str1, i64 0, i64 0            ;
> <i8*> [#uses=1]
>         call i8* @strcat( i8* %str3, i8* %str4 )                ;
<i8*>:0
> [#uses=0]
>         %tmp6 = call i32 @puts( i8* %str3 )             ; <i32>
[#uses=0]
>         %str9 = getelementptr [8 x i8]* @.str8, i64 0, i64 0            ;
> <i8*> [#uses=2]
>         %str10 = getelementptr [7 x i8]* @.str7, i64 0, i64 0           ;
> <i8*> [#uses=1]
>         call i8* @strcat( i8* %str9, i8* %str10 )               ;
<i8*>:1
> [#uses=0]
>         %tmp12 = call i32 @puts( i8* %str9 )            ; <i32>
[#uses=0]
>         ret i32 0
> }
>
>
> writes:
> %
> hello world
> mother orld
>
>
> I tried decompile code:
>  main(int argc, char **argv) {
>   char str1[] = "mother ";
>   strcat(str1, "father");
>   return 0;
> }
>
> decompiler gives to me code, in this code string " mother\0"
presents as:
>
> %str1 > alloca [8 x i8], align 16		; <[8 x i8]*> [#uses=9]
> 	%tmp1 = getelementptr [8 x i8
> ]* %str1, i32 0, i32 0		; <i8*> [#uses=2]
> 	store i8 109, i8* %tmp1, align 16
> 	%tmp4 = getelementptr [8 x i8]* %str1, i32 0,
> i32 1		; <i8*> [#uses=1]
> 	store i8 111, i8* %tmp4, align 1
> 	%tmp7 > getelementptr [8 x i8]* %str1, i32 0, i32 2		; <i8*>
[#uses=1]
> 	
> store i8 116, i8* %tmp7, align 1
> 	%tmp10 = getelementptr [8 x i8]* %str1,
> i32 0, i32 3		; <i8*> [#uses=1]
> 	store i8 104, i8
> * %tmp10, align 1
> 	%tmp13 = getelementptr [8 x i8]* %str1, i32 0, i32 4		; <
> i8*> [#uses=1]
> 	store i8 101, i8* %tmp13, align 1
> 	%tmp16 = getelementptr [8 x i8]* %str1, i32 0, i32 5		; <i8*>
[#uses=1]
> 	store
> i8 114, i8* %tmp16, align 1
> 	%tmp19 = getelementptr [8 x i8]* %str1, i32 0,
> i32 6		; <i8*> [#uses=1]
> 	store i8 32, i8* %tmp19, align 1
> 	%tmp22 > getelementptr [8 x i8]* %str1, i32 0, i32 7		; <i8*>
[#uses=1]
>
> 	
> store i8 0, i8* %tmp22, align 1
>
>
> it's looks funny, can you say another less complex way to do this
> operation?
> Thanks
>
> Best regards,
>     Zalunin Pavel
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>

-- 
Syed Faraz Mahmood
web  :  http://www.farazmahmood.com
blog  :  http://farazmahmood.wordpress.com
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Richard Pennington

2008-Jan-06 21:09 UTC

head link

[LLVMdev] Another memory fun

Zalunin Pavel wrote:> hm.... I think, that is valid in c
[snip]> I tried decompile code:
>  main(int argc, char **argv) {
>   char str1[] = "mother ";
>   strcat(str1, "father");
>   return 0;
> }
> 
This is valid C but you forget that str1 is not magically expanded by 
strcat. It starts out as, and remains a char array with 8 elements.
> decompiler gives to me code, in this code string " mother\0"
presents as:
> 
> %str1 = 
> alloca [8 x i8], align 16		; <[8 x i8]*> [#uses=9]
> 	%tmp1 = getelementptr [8 x i8
> ]* %str1, i32 0, i32 0		; <i8*> [#uses=2]
> 	store i8 109, 
> i8* %tmp1, align 16
> 	%tmp4 = getelementptr [8 x i8]* %str1, i32 0, 
> i32 1		; <i8*> [#uses=1]
> 	store i8 111, i8* %tmp4, align 1
> 	%tmp7 = 
> getelementptr [8 x i8]* %str1, i32 0, i32 2		; <i8*> [#uses=1]
> 	
> store i8 116, i8* %tmp7, align 1
> 	%tmp10 = getelementptr [8 x i8]* %str1, 
> i32 0, i32 3		; <i8*> [#uses=1]
> 	store i8 104, i8
> * %tmp10, align 1
> 	%tmp13 = getelementptr [8 x i8]* %str1, i32 0, i32 4		; <
> i8*> [#uses=1]
> 	store i8 101, i8* %tmp13, align 1
> 	%tmp16 = getelementptr [8 x 
> i8]* %str1, i32 0, i32 5		; <i8*> [#uses=1]
> 	store 
> i8 114, i8* %tmp16, align 1
> 	%tmp19 = getelementptr [8 x i8]* %str1, i32 0, 
> i32 6		; <i8*> [#uses=1]
> 	store i8 32, i8* %tmp19, align 1
> 	%tmp22 = 
> getelementptr [8 x i8]* %str1, i32 0, i32 7		; <i8*> [#uses=1]
> 
> 	
> store i8 0, i8* %tmp22, align 1
> 
> 
> it's looks funny, can you say another less complex way to do this
operation?
> Thanks
Another way:

define i32 @main(i32, i8**) {
entry:
         %argc = alloca i32              ; <i32*> [#uses=1]
         store i32 %0, i32* %argc
         %argv = alloca i8**             ; <i8***> [#uses=1]
         store i8** %1, i8*** %argv
         %retval = alloca i32            ; <i32*> [#uses=3]
         store i32 0, i32* %retval
         %str1 = alloca [8 x i8]         ; <[8 x i8]*> [#uses=2]
         bitcast [8 x i8]* %str1 to i8*          ; <i8*>:2 [#uses=1]
         call void @llvm.memcpy.i32( i8* %2, i8* getelementptr ([8 x 
i8]* @.str, i32 0, i32 0), i32 ptrtoint (i8* getelementptr (i8* null, 
i32 1) to i32), i32 0 )
         bitcast [8 x i8]* %str1 to i8*          ; <i8*>:3 [#uses=1]
         call i8* @strcat( i8* %3, i8* getelementptr ([7 x i8]* @.str1, 
i32 0, i32 0) )          ; <i8*>:4 [#uses=0]
         store i32 0, i32* %retval
         br label %return

return:         ; preds = %entry
         load i32* %retval               ; <i32>:5 [#uses=1]
         ret i32 %5
}


It will still segfault, however. ;-)

-Rich

Zalunin Pavel

2008-Jan-06 23:27 UTC

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[LLVMdev] Another memory fun

so, thanx to all....

now I understand my fault and now I have another question:

how I can write those code with using API:

%final = alloca [256 x i8], align 16            ; <[256 x i8]*> [#uses=1]
        %final1 = getelementptr [256 x i8]* %final, i32 0, i32
0                ; <i8*> [#uses=2]
        call void @llvm.memcpy.i32( i8* %final1, i8* getelementptr ([3 x
i8]* @.str, i32 0, i32 0), i32 3, i32 1 )
        %tmp5 = call i8* bitcast (i8* (i8*, i8*)* @strcat to i8* (i8*
noalias , i8* noalias )*)( i8* %final1 noalias , i8* getelementptr ([4 x
i8]* @.str1, i32 0, i32 0) noalias  )          ; <i8*> [#uses=0]
        ret i32 1



I interested for last string :
    %tmp5 = call i8* bitcast (i8* (i8*, i8*)* @strcat to i8* (i8* noalias ,
i8* noalias )*)( i8* %final1 noalias , i8* getelementptr ([4 x i8]* @.str1,
i32 0, i32 0) noalias  )          ; <i8*> [#uses=0]

Best Regards,
   Zalunin Pavel
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