Move DateMath weekdayName/monthName arrays to .rodata section

Move DateMath weekdayName/monthName arrays to .rodata section

Move WTF::DateMath's weekdayName/monthName arrays from
.data.rel.ro.local section to .rodata section by leveraging the
fact that all the strings held in these arrays have the same size.
We can therefore define the arrays as:
const char weekdayName[7][4] = { ... };
instead of
const char* const weekdayName[7] = { ... };

This gets rid of all pointers and enables placing these arrays in
readonly memory.

This makes sure that they are shared between different library
instances, and should help saving RAM on mobile. This also reduces
the number of relocations in libchromeview_prebuilt.so by 31
according to relinfo.

BUG=249746
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=159981

[Inactive, 2013-10-18 15:48:32]

relinfo output:
before: out/Release/lib/libchromeview_prebuilt.so: 240776 relocations, 240715
relative (99%), 329 PLT entries, 0 for local syms (0%), 0 users
after: out/Release/lib/libchromeview_prebuilt.so: 240745 relocations, 240684
relative (99%), 329 PLT entries, 0 for local syms (0%), 0 users

Objdump ( objdump -x out/Release/lib/libchromeview_prebuilt.so | grep ...)
-Before:
021a71d0 l     O .data.rel.ro.local	00000030 _ZN3WTFL9monthNameE
021a9658 l     O .data.rel.ro.local	0000001c _ZN3WTFL11weekdayNameE

- After:
018d69b6 l     O .rodata	00000030 _ZN3WTFL9monthNameE
01a10cf6 l     O .rodata	0000001c _ZN3WTFL11weekdayNameE

[abarth-chromium, 2013-10-18 15:59:50]

lgtm

Nice!

[commit-bot: I haz the power, 2013-10-18 16:00:12]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/29293002/1

[commit-bot: I haz the power, 2013-10-19 00:27:12]

Change committed as 159981

[eseidel, 2013-10-19 01:26:21]

How much is on the table here?  How much do we expect to move in this way?

[Inactive, 2013-10-20 15:03:48]

On 2013/10/19 01:26:21, eseidel wrote:
> How much is on the table here?  How much do we expect to move in this way?

We move 19 words of data to readonly memory (due to the 12+7=19 pointers), so 76
bytes on my 32-bit phone. I confirmed this using the following command:
size -A -d DateMath.o

My understanding is that the strings themselves were already in readonly memory.

We also get rid of 31 relocations, which affects startup time.

We also potentially increase security by moving those arrays to readonly memory.
To be fair, the linker could already take away write access to this data but
only *after* the relocations (as the pointers were marked as const).