linux-kernel - [PATCH 1/2 v2] FLAT: split the stack & data alignments

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Message-Id: <1274863506-14168-1-git-send-email-vapier@gentoo.org>
Date:	Wed, 26 May 2010 04:45:05 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	uclinux-dev@...inux.org, David Howells <dhowells@...hat.com>,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	Paul Mundt <lethal@...ux-sh.org>
Cc:	uclinux-dist-devel@...ckfin.uclinux.org,
	microblaze-uclinux@...e.uq.edu.au, Michal Simek <monstr@...str.eu>,
	linux-m32r@...linux-m32r.org,
	Hirokazu Takata <takata@...ux-m32r.org>,
	linux-kernel@...r.kernel.org,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: [PATCH 1/2 v2] FLAT: split the stack & data alignments

The stack and data have different alignment requirements, so don't force
them to wear the same shoe.  Increase the data alignment to match that
which the elf2flt linker script has always been using: 0x20 bytes.  Not
only does this bring the kernel loader in line with the toolchain, but
it also fixes a swath of gcc tests which try to force larger alignment
values but randomly fail when the FLAT loader fails to deliver.

Signed-off-by: Mike Frysinger <vapier@...too.org>
---
v2
	- split changes & document better

 fs/binfmt_flat.c |   23 +++++++++++++++--------
 1 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index 49566c1..b865622 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -56,15 +56,22 @@
 #endif
 
 /*
- * User data (stack, data section and bss) needs to be aligned
- * for the same reasons as SLAB memory is, and to the same amount.
- * Avoid duplicating architecture specific code by using the same
- * macro as with SLAB allocation:
+ * User data (data section and bss) needs to be aligned.
+ * We pick 0x20 here because it is the max value elf2flt has always
+ * used in producing FLAT files, and because it seems to be large
+ * enough to make all the gcc alignment related tests happy.
+ */
+#define FLAT_DATA_ALIGN	(0x20)
+
+/*
+ * User data (stack) also needs to be aligned.
+ * Here we can be a bit looser than the data sections since this
+ * needs to only meet arch ABI requirements.
  */
 #ifdef ARCH_SLAB_MINALIGN
-#define FLAT_DATA_ALIGN	(ARCH_SLAB_MINALIGN)
+#define FLAT_STACK_ALIGN	(ARCH_SLAB_MINALIGN)
 #else
-#define FLAT_DATA_ALIGN	(sizeof(void *))
+#define FLAT_STACK_ALIGN	(sizeof(void *))
 #endif
 
 #define RELOC_FAILED 0xff00ff01		/* Relocation incorrect somewhere */
@@ -129,7 +136,7 @@ static unsigned long create_flat_tables(
 
 	sp = (unsigned long *)p;
 	sp -= (envc + argc + 2) + 1 + (flat_argvp_envp_on_stack() ? 2 : 0);
-	sp = (unsigned long *) ((unsigned long)sp & -FLAT_DATA_ALIGN);
+	sp = (unsigned long *) ((unsigned long)sp & -FLAT_STACK_ALIGN);
 	argv = sp + 1 + (flat_argvp_envp_on_stack() ? 2 : 0);
 	envp = argv + (argc + 1);
 
@@ -876,7 +883,7 @@ static int load_flat_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 	stack_len = TOP_OF_ARGS - bprm->p;             /* the strings */
 	stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */
 	stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */
-	stack_len += FLAT_DATA_ALIGN - 1;  /* reserve for upcoming alignment */
+	stack_len += FLAT_STACK_ALIGN - 1;  /* reserve for upcoming alignment */
 	
 	res = load_flat_file(bprm, &libinfo, 0, &stack_len);
 	if (IS_ERR_VALUE(res))
-- 
1.7.1

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