hi all, I am a newbie of Linux and now have a job with it, recently I meet a puzzle : when I use inline asembly code and a makefile with many optimize options open, the compile result is ok, while run with a segment fault error. the following is a test code:
-----------------------------------------------------
#include <stdio.h>
#include <memory.h>
typedef unsigned char UChar;
void RGB_test(UChar* pRGBOutBuf, UChar* pRGBInBuf, int width, int height)
{
int loop_num;
loop_num = (width * height) >> 3;

__asm__
(
"movl %0, %%eax \n\t"
"movl %1, %%ebx \n\t"
"movl %2, %%ecx \n\t"

"loop1: \n\t"
"movq (%%ebx), %%mm0 \n\t"
"movq %%mm0, (%%eax) \n\t"
"addl $8, %%eax \n\t"
"addl $8, %%ebx \n\t"
"dec %%ecx \n\t"
"jnz loop1 \n\t"
"emms \n\t"
:
:"m"(pRGBOutBuf), "m"(pRGBInBuf), "m"(loop_num)
:"%eax", "%ebx", "%ecx"
);
}
int main(int argc, char* argv[])
{
UChar* pRGBIn = new UChar[320 * 240];
UChar* pRGBOut = new UChar[320 * 240];

memset(pRGBIn, 0xff, 320*240);
RGB_test(pRGBOut, pRGBIn, 320, 240);

FILE * pfile_out=NULL;
pfile_out= fopen("test", "wb");
fwrite(pRGBOut, sizeof(UChar), 320*240, pfile_out); //attention!

fclose(pfile_out);
delete pRGBIn;
delete pRGBOut;
return 1;
}
--------------------------------------------------------
The segment fault when run to "fwrite", which always get a null pointer of pfile_out.

and the makefile is:
--------------------------------------------------------
CXX := /usr/bin/g++
OPT := -march=pentiumpro -mcpu=pentiumpro -fomit-frame-pointer -O1 -fno-exceptions -fno-rtti -fPIC

SRC = RGB_test.cpp
OBJ = RGB_test.o
all: $(SRCS)
$(CXX) $(OPT) -g -c $(SRC)
$(CXX) -Wall -o RGB_test -g $(OBJ)

clean :
rm RGB_test $(OBJ)
--------------------------------------------------------
when -fomit-frame-pointer or fPIC is omitted from the makefile, the code runs ok.

Thans for your help!

You should always test the return value of fopen() to see if it is NULL. If it is, you should print out the value of errno (#include<errno.h>) to see what the error was.
You can print a human-readable form of the error with printf("%s", strerror(errno)); (for which you also need to include string.h).

Thanks for ur advice, in fact if I add a judge like this:
-----------------------------------------
if (pfileOut == NULL)
{
printf("%s", strerror(errno)); // or printf("anystring");
return -1;
}
------------------------------------------
nothing will be print out! and debug with gdb, the errno is 22, which is "invalid argument".

now find a clue, that if the EBX is not used, the result is ok, but the reason is not found and the trouble is not solved yet.