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Re: Flag to disable wchar support

On 21/02/10 07:06 AM, Federico Terraneo wrote: 
Sorry to bother you, but got no answer on this, so I'm trying to ask the
same question again. Hope it is allowed by the mailing list policy.


No problem.

Federico Terraneo wrote: 
Hi,
I've been using newlib + libstdc++ for quite some time compiled with
"--target=arm-elf", but I'm switching to "--target=arm-eabi" for
better support of new Cortex M3 microcontrollers.

However, this change caused a large code size increase in C++ code
(see below), and the problem seems related to newlib.
In practice, compiling newlib 1.18.0 with "--target=arm-eabi" causes
the inclusion of some new functions to support wide charactes, like
wprintf and wscanf (for the full list see below), and this triggers
libstdc++ into including support for wide characters in iostream code,
which is what causes the code size increase.


Newlib is a library of functions that are brought in if referenced. The ar displayed below is for libc.a. The size of libc.a is meaningless for a statically linked application. You need to determine what library functions are being brought in to the application and from where. There are some inter-library references (i.e. some library functions get dragged in by others), but this will not change across the configurations you have mentioned for the same newlib.

If libstdc++ for arm-eabi calls a wchar function and for arm-elf it doesn't, that is not newlib's fault.

So I'm asking these two questions:
1) Is it "normal" that these additional functions are included only
with "--target=arm-eabi" and not with "--target=arm-elf"?

No. They are not under configuration triplet control. If you use ELIX level 3, you can remove some of them from the library. I just noticed there looks like a bug in the Makefile.am which includes a few ELIX 4 (also the default) items via additional objects regardless of the ELIX level.

Places to look for configuration differences in newlib is the configure.host file and in the libc/include/sys/config.h file.

2) Is there a way to disable wide character support?
I've tried "--disable-newlib-mb" but it didn't work.


Have you confirmed that --disable-newlib-mb did not work? If you look at the newlib.h header file you create in your build/arm-*/newlib directory, the value _MB_CAPABLE should be #undef'd out. The option does not remove the wchar functions, it simply makes them smaller since they don't have to do any real work (e.g. converting from mb to wchar is simple if all characters are single-byte). You can still reference the functions and if you do, the smaller versions get dragged in.

-- Jeff J.

For now I've temporarily fixed the problem by downgrading t
o newlib 
1.17.0 since it does not have these new functions and code size
returned at acceptable levels, but I'd like to stay up to date with
the latest newlib.

-------------------------------------------------------

An example program to show the difference in code size between arm-elf
and arm-eabi

#include <iostream>
using namespace std;

int main()
{
cout<<"Hello world"<<endl;
string line;
getline(cin,line);
cout<<line;
}

arm-elf-g++ -mcpu=arm7tdmi -g -O0 -c arm_test.cpp
arm-elf-g++ -mcpu=arm7tdmi -o arm_test arm_test.o
arm-elf-size arm_test
text data bss dec hex filename
368320 2648 3880 374848 5b840 arm_test

arm-eabi-g++ -mcpu=arm7tdmi -g -O0 -c arm_test.cpp
arm-eabi-g++ -mcpu=arm7tdmi -o arm_test arm_test.o
arm-eabi-size arm_test
text data bss dec hex filename
504292 2756 7468 514516 7d9d4 arm_test

-------------------------------------------------------

The list of functions that are present only when compiling with
"--target=arm-elf"

$ arm-eabi-ar -t /opt/arm-eabi/arm-eabi/lib/libc.a | sort >
~/libc-eabi.txt
$ arm-elf-ar -t /opt/arm-elf/arm-elf/lib/libc.a | sort > ~/libc-elf.txt
$ diff -U 0 libc-elf.txt libc-eabi.txt
--- libc-elf.txt 2010-02-07 11:22:50.000000000 +0100
+++ libc-eabi.txt 2010-02-07 11:22:41.000000000 +0100
@@ -99,0 +100 @@
+lib_a-fpurge.o
@@ -117,0 +119 @@
+lib_a-fwprintf.o
@@ -118,0 +121 @@
+lib_a-fwscanf.o
@@ -211,0 +215 @@
+lib_a-mbsnrtowcs.o
@@ -224,0 +229 @@
+lib_a-mkdirr.o
@@ -269,0 +275 @@
+lib_a-sb_charsets.o
@@ -283,0 +290 @@
+lib_a-sf_fpclassify.o
@@ -292,0 +300 @@
+lib_a-s_fpclassify.o
@@ -350,0 +359 @@
+lib_a-strtold.o
@@ -360,0 +370,2 @@
+lib_a-svfiwprintf.o
+lib_a-svfiwscanf.o
@@ -362,0 +374,2 @@
+lib_a-svfwprintf.o
+lib_a-svfwscanf.o
@@ -363,0 +377,2 @@
+lib_a-swprintf.o
+lib_a-swscanf.o
@@ -395 +409,0 @@
-lib_a-_tolower.o
@@ -397 +410,0 @@
-lib_a-_toupper.o
@@ -423,0 +437,2 @@
+lib_a-vfiwprintf.o
+lib_a-vfiwscanf.o
@@ -425,0 +441,2 @@
+lib_a-vfwprintf.o
+lib_a-vfwscanf.o
@@ -435,0 +453,4 @@
+lib_a-vswprintf.o
+lib_a-vswscanf.o
+lib_a-vwprintf.o
+lib_a-vwscanf.o
@@ -439,0 +461 @@
+lib_a-wcscasecmp.o
@@ -445,0 +468,2 @@
+lib_a-wcsdup.o
+lib_a-wcsftime.o
@@ -448,0 +473 @@
+lib_a-wcsncasecmp.o
@@ -452,0 +478 @@
+lib_a-wcsnrtombs.o
@@ -457,0 +484 @@
+lib_a-wcstod.o
@@ -458,0 +486 @@
+lib_a-wcstold.o
@@ -479,0 +508 @@
+lib_a-wprintf.o
@@ -480,0 +510 @@
+lib_a-wscanf.o





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