binfmt_elf::create_elf_tables changes u_platform without refill

Hi all...

I thing I found a bug in 2.4 (and someone should check if this applies to 2.5 also...). In short, when running on an HT box, create_elf_tables() changes u_platform pointer (to separate stacks and avoid cache wars), without copy_to_user'ing again.

Current code:

    if (k_platform) {
        platform_len = strlen(k_platform) + 1;
        u_platform = p - platform_len;
        __copy_to_user(u_platform, k_platform, platform_len);
    } else

...
#if defined(__i386__) && defined(CONFIG_SMP)
if(smp_num_siblings > 1)
u_platform = u_platform - ((current->pid % 64) << 7);
///// So original u_platform with data is lost !!! #endif
...

    sp = (elf_addr_t *)(~15UL & (unsigned long)(u_platform));  // Set stack
...
    if (k_platform) {
        sp -= 2;
        NEW_AUX_ENT(0, AT_PLATFORM, (elf_addr_t)(unsigned long) u_platform);
///// What the h**l is copied here after changing u_platform ???
    }

Patch below (use an independent stack_top). Boots and works on my dual Xeon, and glibc behaves correctly:

@@ -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 % 64) << 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

One question: why the 64 value ? Because linux supports 64 processors ? Why not just 2, because you have two siblings at most ?

TIA

J.A. Magallon <[email protected]>      \                 Software is like sex:
werewolf.able.es                         \           It's better when it's free
Mandrake Linux release 9.1 (Cooker) for i586
Linux 2.4.21-pre2-jam1 (gcc 3.2.1 (Mandrake Linux 9.1 3.2.1-2mdk))

[...]

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Better, shouldn't this be NR_CPUS ? So you save half stack space on ia32, or even more with CONFIG_NR_CPUS...

J.A. Magallon <[email protected]>      \                 Software is like sex:
werewolf.able.es                         \           It's better when it's free
Mandrake Linux release 9.1 (Cooker) for i586
Linux 2.4.21-pre2-jam1 (gcc 3.2.1 (Mandrake Linux 9.1 3.2.1-2mdk))