tested with a cross-compiler i686-pc-linux-gnu-gcc (GCC) 3.4.4 and the suse 10.1 native gcc (GCC) 4.1.0 (SUSE Linux) -----Original Message----- From: gcc-help-owner@xxxxxxxxxxx [mailto:gcc-help-owner@xxxxxxxxxxx] On Behalf Of Woytech Karl-Heinz Sent: Donnerstag, 05. Oktober 2006 11:35 To: gcc-help@xxxxxxxxxxx Subject: incorrect dereference of implicit memcpy Hello, I am working on an x86 embedded system where we do not have ld/libc onboard. our OS provides basic libc functions and does it's own dynamic linking for the applications. Basic function dereferencing works properly, our problem is with the implicit function calls that gcc makes for copying structs. When the application code below gets started our OS finds the 'imex' structure and correctly fills out the required function pointers so that calls to the fn's result in the code provided by the os getting called. Thus the explicit call jimbob(815); translates to push $0x32f call *0x804912c memcpy (dest, src, 20); translates to push $0x14 push %ebx lea 0xffffff61(%ebp),%eax push %eax call *0x8049128 which is also good BUT the structure copy x=y becomes push $0x16 push %eax push %edx call 8049128 <- no '*' which is a direct jump into memory instead of a jump to the dereference of the memory location. as of that moment the application crashes. below are our build commands and the program. Am I doing something wrong here, or do i have incorrect cflags/ldflags? ie can i get gcc to produce the same derefecenced call as per the explicit calls? Thanks in advance for any input Charlie gcc testjmp.c -c -o testjmp.o -ffreestanding -march=i386 -g -Os -fno-builtin ld testjmp.o -o testjmp -static -nostdlib objdump testjmp -DSx > testjmp.dis testjmp.c: // structure def for our import/export table typedef struct imex_s { char name[16]; void *ptr; } imex_t; // fixed typedefs for our funcions typedef int (*jimbob_t)(int jb); typedef void (*memcpy_t)(char *d, char *s, int l); // memory space for the to be linked fn's will be in .bss jimbob_t jimbob; memcpy_t memcpy; // our import table will be in .const const imex_t imex[] = { { "jimbob", (void*)&jimbob}, { "memcpy", (void*)&memcpy} }; // test struct for x=y typedef struct { char Bytes[22]; } structure_t; int main(int argc, char *argv[]) { char dest[100]; char src[] = {"hello pdts"}; volatile structure_t X, Y; jimbob(815); memcpy (dest, src, 20); X = Y; /* gcc creates a memcpy here */ return 0; }// main
