For some time I've noted but have never bothered chasing down the *printf
problems associated with using -msoft-float/-D_SOFT_FLOAT on Linux/PPC.
Needing to remedy the issue, I started chasing it down using the code
samples below. When compiled using just '$(CROSS_COMPILE)gcc -o pi-test
*.c' everything works fine:
user at host% ./pi-test
The value of Pi is approximately: 3.142857
If I turn-around and compile it with '$(CROSS_COMPILE)gcc -o pi-test
-msoft-float *.c' or '$(CROSS_COMPILE)gcc -o pi-test -msoft-float
-D_SOFT_FLOAT *.c' I get:
user at host% ./pi-test
The value of Pi is approximately: 0.000000
After disassembling the code, from what I can see both bits of code are
generating the right output for the IEEE single-precision result. Both
bits of code appear to be following the correct register callee/caller
convetions for both 'pi' and 'float_print'. So, I have to assume that the
problem lies somewhere within either the '__extendsfdf2' or 'printf'
subroutine calls within 'float_print':
Disassembly of section .text:
00000000 <float_print>:
0: 94 21 ff e0 stwu r1,-32(r1)
4: 7c 08 02 a6 mflr r0
8: 93 e1 00 1c stw r31,28(r1)
c: 90 01 00 24 stw r0,36(r1)
10: 7c 3f 0b 78 mr r31,r1
14: 90 7f 00 08 stw r3,8(r31)
18: 90 9f 00 0c stw r4,12(r31)
1c: 80 7f 00 0c lwz r3,12(r31)
20: 48 00 00 01 bl __extendsfdf2
24: 7c 69 1b 78 mr r9,r3
28: 7c 8a 23 78 mr r10,r4
2c: 3d 60 00 00 lis r11,.rodata at h
30: 38 6b 00 00 addi r3,r11,.rodata at l
34: 80 9f 00 08 lwz r4,8(r31)
38: 7d 25 4b 78 mr r5,r9
3c: 7d 46 53 78 mr r6,r10
40: 48 00 00 01 bl printf
44: 7c 60 1b 78 mr r0,r3
48: 7c 03 03 78 mr r3,r0
4c: 48 00 00 04 b 50 <float_print+0x50>
50: 81 61 00 00 lwz r11,0(r1)
54: 80 0b 00 04 lwz r0,4(r11)
58: 7c 08 03 a6 mtlr r0
5c: 83 eb ff fc lwz r31,-4(r11)
60: 7d 61 5b 78 mr r1,r11
64: 4e 80 00 20 blr
I've heard and have read in back messages that this problem lies in either
the varags implementation or in the stdio-common (i.e. printf) bits of
glibc. Does anyone have a patch which addresses this specific problem?
This problem happens on both a Solaris/SPARC to Linux/PPC cross compiler
as well as on a native Linux/PPC compiler. The former is
gcc-2.95.3-20010112 (prerelease) with glibc-2.1.3 and the latter is
gcc-2.95.2-19991024 (release/franzo) with 'glibc-2.1.3 from
'glibc-2.1.3-4a'.
For the cross-compiler, the compiler and libraries were configured w/
GCC:
./configure --host=sparc-sun-solaris2.7 --target=powerpc-linux
--prefix=$TOOLROOT/host/sparc-sun-solaris
--with-headers=$TOOLROOT/target/powerpc-linux-gnu/include
--with-libs=$TOOLROOT/target/powerpc-linux-gnu/lib
--enable-shared --enable-languages=c,c++
--with-cpu=403 --without-fp
GLIBC:
./configure --host=powerpc-linux --with-headers=/usr/src/linux/include
--enable-shared --enable-add-ons=crypt,linuxthreads
--prefix=$TOOLROOT/target/powerpc-linux-gnu --without-fp
The test code:
main.c:
int main (void)
{
float value;
int status;
value = pi();
status = float_print("The value of Pi is approximately", value);
return (status);
}
pi.c:
float
pi(void)
{
return (22.0/7.0);
}
float_print.c:
int float_print(const char *string, float value)
{
return (printf("%s: %f\n", string, value));
}
--
Grant Erickson University of Minnesota Alumni
o mail:erick205 at umn.edu 1996 BSEE
o http://www.umn.edu/~erick205 1998 MSEE
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
