PtrPosCharPairSearch not working with valgrind #79

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opened 2021-08-08 23:55:33 +00:00 by benibela · 1 comment

benibela commented

2021-08-08 23:55:33 +00:00

(Migrated from github.com)

Consider:

var s: string;
begin
 s := 'ABRACA';
 s += 'DABRA';
 writeln(PtrPosCharPair('A', 'B', pchar(s), 11, 2));

Prints 5 as it should.

Calling the same program with valgrind, it prints -1 (PtrPosCharPairSearch returns 0)

fpc 3.2.2 on linux64, valgrind-3.16.1

When I tried to initialized the string with s := 'ABRACADABRA', it worked the first time even with valgrind, but now it stopped working.

It also seems to work with every other string. Like 'xABRACADABRA'. Or

 for i := 1 to 10 do begin
   s := '';
   s += 'ABRACA';
   for j := 1 to i do s += 'A';
   s += 'DABRA';
   writeln(PtrPosCharPair('A', 'B', pchar(s), 11 + i, 2  ));
 end;

Consider: var s: string; begin s := 'ABRACA'; s += 'DABRA'; writeln(PtrPosCharPair('A', 'B', pchar(s), 11, 2)); Prints `5` as it should. Calling the same program with valgrind, it prints `-1` (PtrPosCharPairSearch returns 0) fpc 3.2.2 on linux64, valgrind-3.16.1 When I tried to initialized the string with `s := 'ABRACADABRA'`, it worked the first time even with valgrind, but now it stopped working. It also seems to work with every other string. Like `'xABRACADABRA'`. Or ``` for i := 1 to 10 do begin s := ''; s += 'ABRACA'; for j := 1 to i do s += 'A'; s += 'DABRA'; writeln(PtrPosCharPair('A', 'B', pchar(s), 11 + i, 2 )); end; ```

benibela commented

2021-08-09 00:12:37 +00:00

(Migrated from github.com)

movdqa xmm2,[rdi]
movdqa xmm3,[rdi]
movdqa xmm4,[rdi+16]
movdqa xmm5,[rdi+16]

That assumes rdi is aligned, does it not?

But it is not aligned since the offset is 2...

edit: Ok, the and rdi,-32 makes it aligned. But then it is reading from the string header

>``` > movdqa xmm2,[rdi] > movdqa xmm3,[rdi] > movdqa xmm4,[rdi+16] > movdqa xmm5,[rdi+16] >``` That assumes rdi is aligned, does it not? But it is not aligned since the offset is 2... edit: Ok, the `and rdi,-32` makes it aligned. But then it is reading from the string header