From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)
To: drow@false.org
Cc: gcc@gcc.gnu.org
Subject: Re: Problem with ARM_DOUBLEWORD_ALIGN on ARM
Date: Thu, 22 Nov 2007 08:00:00 -0000 [thread overview]
Message-ID: <10711212107.AA27608@vlsi1.ultra.nyu.edu> (raw)
In-Reply-To: <20071121210156.GA15755@caradoc.them.org>
> Do you have any test cases? I'm pretty sure this works, at least in
> the usual cases.
They're going to be hard to construct since they are sensitive to such
things as the number of registers saved.
> A wild guess says that you're doing this in Ada. It may be something
> specific to the nested case then.
It is in Ada, but I don't think the nested case is the cause of the
particular problem I ran into (it does need to be fixed anyway, though,
since it might bite later). I suspect the case we're running into is
either the args to push or the registers saved.
Here's a description of the miscompilation we saw:
> Specifically, in Ada.Text_IO.Put_Line, we end up calling memcpy
> with a buffer allocated using "alloca". The alloca result
> is aligned to a multiple of 8, but the corresponding operation
> on the stack pointer is eliminated because combine assumes
> the stack is aligned already.
>
> Specifically, in the example below, the assignment to
> Buffer (1 .. Ilen) is done through memcpy, but
> memcpy overwrites the return address.
>
> From a-textio.adb, around line 1450:
>
> -- Now prepare the string with its terminator
>
> declare
> Buffer : String (1 .. Ilen + 2);
> Plen : size_t;
>
> begin
> Buffer (1 .. Ilen) := Item (Istart .. Item'Last);
> Buffer (Ilen + 1) := Character'Val (LM);
When you look at the disassembled code, we saw an update to the stack
pointer in the prologue of a number that wasn't a multiple of 8 (it
was 36, if I remember correctly).
next prev parent reply other threads:[~2007-11-21 21:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-21 23:32 Richard Kenner
2007-11-22 7:22 ` Daniel Jacobowitz
2007-11-22 8:00 ` Richard Kenner [this message]
2007-11-22 15:30 Geert Bosch
2007-11-26 10:34 ` Daniel Jacobowitz
2007-12-26 20:05 ` Mark Mitchell
2007-12-26 22:44 ` Geert Bosch
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