Apple-2gs-SW/hush
1
0
Fork 0
mirror of https://github.com/sheumann/hush.git synced 2024-12-21 23:29:34 +00:00
Code Issues Projects Releases Wiki Activity

add info about gcc's sadistic alignment - and how to disable it

Browse Source
This commit is contained in:
Denis Vlasenko 2007-03-21 10:07:01 +00:00
parent afa37cf508
commit b8e72fdde1
1 changed files with 26 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
docs/keep_data_small.txt
View File

@ -178,5 +178,29 @@ struct {
char vc31[31] = { 1 }; // unaligned
char vc32[32] = { 1 }; // aligned to 32 bytes
-fpack-struct=1 reduces alignment of s28 to 1 (but probably will break layout
of many libc structs) but s32 and vc32 are still aligned to 32 bytes.
-fpack-struct=1 reduces alignment of s28 to 1 (but probably
will break layout of many libc structs) but s32 and vc32
are still aligned to 32 bytes.
I will try to cook up a patch to add a gcc option for disabling it.
Meanwhile, this is where it can be disabled in gcc source:
gcc/config/i386/i386.c
int
ix86_data_alignment (tree type, int align)
{
#if 0
if (AGGREGATE_TYPE_P (type)
&& TYPE_SIZE (type)
&& TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST
&& (TREE_INT_CST_LOW (TYPE_SIZE (type)) >= 256
|| TREE_INT_CST_HIGH (TYPE_SIZE (type))) && align < 256)
return 256;
#endif
Result (non-static busybox built against glibc):
# size /usr/srcdevel/bbox/fix/busybox.t0/busybox busybox
text data bss dec hex filename
634416 2736 23856 661008 a1610 busybox
632580 2672 22944 658196 a0b14 busybox_noalign