Re: [linuxsh-dev] Re: bad alignment fixup

[Bryan R. <br...@ix...>]

Philipp Rumpf wrote:

> gas warns about unaligned .longs.  gcc should never generate unaligned
> accesses unless you use weird casting or assembler code.

Basically, I think the problem was with code like this:

---
#include <stdio.h>

struct structone
{
  unsigned short foo;
  unsigned short bar;
  unsigned short moo;
};

struct structtwo
{
  unsigned char blah;
  unsigned long boom;
};

int main(void)
{
        static struct structone bleep = {1, 2, 3};
        static struct structtwo bloop = {1, 2};   

        bleep.foo=1;
        bloop.boom=2;

        printf("%ld",bloop.boom);
        return 0;
}
---

I will test that exact snippet on the SH4 and see if we are still having
problems. If we are, I guess it's due to the linker either not aligning
structtwo or not aligning boom within structtwo?

As far as I know that code is standard, valid ANSI C.

Please note: we're not using the latest toolchain here, and therefore,
can't use the latest kernels. I would hate to go chasing after an
already fixed bug, so I will look into testing the other engineer's code
with the latest stuff as soon as possible.

> shouldn't happen.

indeed.

> It sends a SIGSEGV.  I'm currently looking into adding a siginfo struct
> with sufficient information to emulate unaligned accesses efficiently.

Ok... in this particular case the unaligned access was coming from a
child pthread. Perhaps the pthread parent caught the SIGSEGV and zombied
all the children? (sounds like a b-rate horror film)

> If you don't see your process's exit status your test environment is broken.

Just to make sure--when a process catches, say, a SIGSEGV and hasn't
installed a special handler for it, it's up to the shell to display the
termination message? I am using the BusyBox shell which may not do so,
in which case I will submit a patch to those guys to at least handle
SIGSEGV...

> if the process doesn't die with SEGV there's another kernel bug.

One which may have already been fixed. I will further investigate this
issue when I get some spare time (heh, in a year or two).

Thanks for the reply,

Bryan

-- 
Bryan Rittmeyer
mailto:br...@ix...
Ixia Communications
26601 W. Agoura Rd.
Calabasas, CA 91302