[RFC][PATCH] Correct AT_PLATFORM for HT P4 in 2.4.21

[J.A. Magallon]

Hi all...

Current kernel fails to set AT_PLATFORM when siblings are present, so HT-P4
fails to publish itself as an i686, and ld.so does not pick automatically
i686 optmized libraries.

Explanation of current bug in create_elf_tables::fs/binfmt_elf.c:
u_platform is used both as the place where platform info is copied at the
beginning of the process data area, and as the stack begin:
- if (k_platform), it is copied at stack top, and u_platform is set to the
  beginning of that info.
- if siblings are present, u_platform is moved to avoid cache conflicts and
  predictability
- the address of u_platform is put to user space, but it has changed and now
  does not point to correct info

This patch separates the two uses, stack and u_platform
Note: it also changes the shifting factor from a fixed 64 to NR_CPUS to save
some space...

Comments ?

--- 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 <[e-mail]>      \                 Software is like sex:
werewolf.able.es                         \           It's better when it's free
Mandrake Linux release 9.2 (Cooker) for i586
Linux 2.4.21-jam1 (gcc 3.3 (Mandrake Linux 9.2 3.3-1mdk))