svn commit: trunk/busybox/docs

[vda at busybox.net]

Author: vda
Date: 2007-03-19 09:04:11 -0700 (Mon, 19 Mar 2007)
New Revision: 18165

Log:
expand documentation


Modified:
   trunk/busybox/docs/keep_data_small.txt


Changeset:
Modified: trunk/busybox/docs/keep_data_small.txt
===================================================================
--- trunk/busybox/docs/keep_data_small.txt	2007-03-19 15:15:06 UTC (rev 18164)
+++ trunk/busybox/docs/keep_data_small.txt	2007-03-19 16:04:11 UTC (rev 18165)
@@ -125,3 +125,32 @@
 If applet doesn't use much of global data, converting it to use
 one of above methods is not worth the resulting code obfuscation.
 If you have less than ~300 bytes of global data - don't bother.
+
+
+		gcc's data alignment problem
+
+The following attribute added in vi.c:
+
+static int tabstop;
+static struct termios term_orig __attribute__ ((aligned (4)));
+static struct termios term_vi __attribute__ ((aligned (4)));
+
+reduced bss size by 32 bytes, because gcc sometimes aligns structures to
+ridiculously large values. asm output diff for above example:
+
+ tabstop:
+        .zero   4
+        .section        .bss.term_orig,"aw", at nobits
+-       .align 32
++       .align 4
+        .type   term_orig, @object
+        .size   term_orig, 60
+ term_orig:
+        .zero   60
+        .section        .bss.term_vi,"aw", at nobits
+-       .align 32
++       .align 4
+        .type   term_vi, @object
+        .size   term_vi, 60
+
+gcc doesn't seem to have options for altering this behaviour.