Re: [PATCH] elf loader support for auxvec base platform string

Andrew Morton wrote:

quoted

On Tue, 2008-07-15 at 18:58 -0500, Nathan Lynch wrote:

quoted

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d48ff5f..834c2c4 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c

@@ -131,6 +131,10 @@ static int padzero(unsigned long elf_bss)
 #define STACK_ALLOC(sp, len) ({ sp -= len ; sp; })
 #endif
 
+#ifndef ELF_BASE_PLATFORM
+#define ELF_BASE_PLATFORM NULL
+#endif

Please add a comment which explains what this is.

Please also add a comment telling the world in which header file the
architecture *must* define this macro and then ensure that that header is
included into this file by reliable means.  asm/elf.h looks OK.

Okay.

quoted

quoted

@@ -172,6 +178,19 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 			return -EFAULT;
 	}
 
+	/*
+	 * If this architecture has a "base" platform capability
+	 * string, copy it to userspace.
+	 */
+	u_base_platform = NULL;
+	if (k_base_platform) {
+		size_t len = strlen(k_base_platform) + 1;
+
+		u_base_platform = (elf_addr_t __user *)STACK_ALLOC(p, len);
+		if (__copy_to_user(u_base_platform, k_base_platform, len))
+			return -EFAULT;
+	}

quoted

From my reading, this change will result in no additional code

generation on non-powerpc architectures.  This is good.  If poss, could
you please verify that theory and perhaps drop a note in the changelog
about that?

That was the intent, yes.  However:

$ scripts/bloat-o-meter vmlinux-x86-{before,after}
add/remove: 0/0 grow/shrink: 2/0 up/down: 18/0 (18)
function                                     old     new   delta
init_mm                                      784     800     +16
load_elf_binary                            11946   11948      +2

(x86_64_defconfig, gcc 4.2.3)

The init_mm/mm_struct bloat is expected (although I'd like to avoid
that), but evidently it has some small effect on load_elf_binary.