[LLVMdev] Another memory fun

[Syed Faraz Mahmood]

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
>
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>


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