vb wrote:
Wolfgang, thank you for your reply, let me try to explain myself a bit clearer:
On Wed, Jul 23, 2008 at 8:18 PM, Wolfgang Denk wd@denx.de wrote:
In message f608b67d0807231039i434e96dbvda86590776db2cb0@mail.gmail.com you wrote:
some companies). If these added modules were not written in position independent manner (namely, using structures with multiple stage indirect pointers interleaved with data), the effort to make these modules work in u-boot is very exhausting.
I don't understand what you mean. Either you link statically with the U-Boot image, or you use standalone programs. In both situations no such problem as described by you exists.
we talk here about modules statically linked into the u-boot image. Allow me to illustrate the problem I am trying to solve. Consider adding this code to a u-boot source file on a ppc460gt platform:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv 87a88,105
int do_ptrt (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]);
int (*pf)(struct cmd_tbl_s *, int, int, char *[]) = do_ptrt;
int do_ptrt (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]) { printf ("pointer is %p\n", pf); printf ("function is %p\n", do_ptrt); return 0; }
U_BOOT_CMD( ptrt, CFG_MAXARGS, 1, do_ptrt, "ptrt\n", "" );
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
And this is what happens when this command is invoked:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv => ptrt pointer is fffb2754 function is 0ffb7754 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
So, the value of 'pf' is equal to the address of do_ptrt() *before* relocation. The fact that there is a GOT and a sophisticated linker script did not prevent this from happening.
OK, now I'm curious: what happens if you make the pf() pointer constant? This will (should) change it from an initialized variable in the .data section to a constant in the .rodata section. I'm wondering if the .rodata section gets relocation information where the .data section doesn't.
int do_ptrt (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]);
const int (*pf)(struct cmd_tbl_s *, int, int, char *[]) = do_ptrt;
int do_ptrt (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]) { printf ("pointer is %p\n", pf); printf ("function is %p\n", do_ptrt); return 0; }
Thanks, gvb