[PATCH] AT_PLATFORM on HT-P4

J.A. Magallon
2003-04-05T22:50:48Z

On 04.06, J.A. Magallon wrote:
>
> On 04.04, Marcelo Tosatti wrote:
> >
> > So here goes -pre7. Hopefully the last -pre.
> >
>

This makes P4 Xeon to report correct i686 platform. Without this,
all those people that think its ld.so automatically picks i686 libs
are wrong...

The original code takes u_platform for coyping ELF_PLATFORM, but
also supposes it is the top of stack. This changes when we have
siblings:

if(smp_num_siblings > 1)
u_platform = u_platform - ((current->pid % 64) << 7);

Later:

NEW_AUX_ENT(0, AT_PLATFORM, (elf_addr_t)(unsigned long) u_platform);

that on HT cpus is broken, isn't it ?

This separates the two things, stack top and u_platform. It could be
even cleaner, with something like

stack_top = p;
if (k_platform)
sz = strlen(k_platform)+1
u_platform = stack_top - sz
__copy_to_user(...)
stack_top -= sz
else
u_platform = NULL
...
if(smp_num_siblings > 1)
stack_top = stack_top - ((current->pid % 64) << 7);
...
if (u_platform)
NEW_AUX_ENT(...)

But I have not tested it. Current patch below.

--- linux/fs/binfmt_elf.c.orig 2002-12-28 00:12:32.000000000 +0100
+++ linux/fs/binfmt_elf.c 2002-12-28 00:32:37.000000000 +0100
@@ -116,11 +116,14 @@
elf_caddr_t *argv;
elf_caddr_t *envp;
elf_addr_t *sp, *csp;
+ char *stack_top;
char *k_platform, *u_platform;
long hwcap;
size_t platform_len = 0;
size_t len;

+ stack_top = p;
+
/*
* Get hold of platform and hardware capabilities masks for
* the machine we are running on. In some cases (Sparc),
@@ -135,8 +138,8 @@
platform_len = strlen(k_platform) + 1;
u_platform = p - platform_len;
__copy_to_user(u_platform, k_platform, platform_len);
- } else
- u_platform = p;
+ stack_top = u_platform;
+ }

#if defined(__i386__) && defined(CONFIG_SMP)
/*
@@ -149,15 +152,14 @@
* processors. This keeps Mr Marcelo Person happier but should be
* removed for 2.5
*/
-
if(smp_num_siblings > 1)
- u_platform = u_platform - ((current->pid % 64) << 7);
+ stack_top -= ((current->pid % NR_CPUS) << 7);
#endif

/*
* Force 16 byte _final_ alignment here for generality.
*/
- sp = (elf_addr_t *)(~15UL & (unsigned long)(u_platform));
+ sp = (elf_addr_t *)(~15UL & (unsigned long)(stack_top));
csp = sp;
csp -= (1+DLINFO_ITEMS)*2 + (k_platform ? 2 : 0);
#ifdef DLINFO_ARCH_ITEMS

--
J.A. Magallon <jamagallon@able.es> \ Software is like sex:
werewolf.able.es \ It's better when it's free
Mandrake Linux release 9.2 (Bamboo) for i586
Linux 2.4.21-pre7-jam1 (gcc 3.2.2 (Mandrake Linux 9.2 3.2.2-5mdk))