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RE: memset (0, 0, 0);
- From: "Thomas,Stephen" <stephen dot thomas at superh dot com>
- To: "Geoff Keating" <geoffk at geoffk dot org>
- Cc: <gdb at sources dot redhat dot com>, <newlib at sources dot redhat dot com>, <bug-glibc at gnu dot org>, "McGoogan,Sean" <sean dot mcgoogan at superh dot com>
- Date: Tue, 8 Apr 2003 08:52:39 +0100
- Subject: RE: memset (0, 0, 0);
Which xmalloc are you referring to? The xmalloc in this case is a gdb internal function, defined in gdb/utils.c:
PTR xmalloc (size_t size)
return xmmalloc (NULL, size);
And xmmalloc is:
void * xmmalloc (void *md, size_t size)
if (size == 0)
val = NULL;
val = mmalloc (md, size);
if (val == NULL)
So size=0 does indeed return NULL. Also, I have single stepped this code to verify that this is actually what happens.
SuperH (UK) Ltd.
From: Geoff Keating [mailto:geoffk at geoffk dot org]
Sent: 07 April 2003 18:18
Cc: gdb at sources dot redhat dot com; newlib at sources dot redhat dot com; bug-glibc at gnu dot org; McGoogan,Sean
Subject: Re: memset (0, 0, 0);
"Thomas,Stephen" <stephen dot thomas at superh dot com> writes:
> gdb appears to call memset(0,0,0) from build_regcache() in
> gdb/regcache.c. I can't really claim to understand how this works, but
> this function appears to get called 3 times during gdb initialization:
> static void build_regcache (void)
> int sizeof_register_valid;
> sizeof_register_valid = ((NUM_REGS + NUM_PSEUDO_REGS) * sizeof (*register_valid));
> register_valid = xmalloc (sizeof_register_valid);
> memset (register_valid, 0, sizeof_register_valid);
> On the 1st time of calling, none of the gdbarch stuff is set up, so
> NUM_REGS = NUM_PSEUDO_REGS = 0. So xmalloc gets called with size=0.
> That returns 0 as the 'address', which gets passed to memset. I guess
> this just works OK on other architectures (it does on x86 anyway).
> Easy enough to fix I suppose, but is that really the point?
xmalloc is never supposed to return 0, and in fact, there's code to prevent it:
if (size == 0)
size = 1;
newmem = malloc (size);
xmalloc_failed finishes with
so xmalloc should never return NULL.
- Geoffrey Keating <geoffk at geoffk dot org>