On 6/27/06, David McCullough <[EMAIL PROTECTED]> wrote:
Are you using the ld-elf2flt/elf2flt.ld combo ?
It lays things out in a known way and has a '-move-rodata' option which
will put the rodata in with the .text if it contains no relocation info
needed at runtime.
Something like this on the link line:
XXXX-gcc .... -Wl,-move-rodata ....
The uClinux-dist has this as the default for !MMU systems that can do
XIP,
Cheers,
Davidm
I'm not using ld-elf2flt, but I am using elf2flt.ld.
arm-elf-gcc -mthumb -fPIC -msingle-pic-base -Wl,-q -Telf2flt.ld hello.c -o hello
arm-elf-elf2flt -adp hello hello -o hello.bflt
The ld script that puts .rodata in .text fails, due to GCC referencing
symbols in .rodata with a GOTOFF32 relocation. So, I used the other
linker script instead, which put .rodata in .data after the .got. This
got me as far as an XIP "Hello, world!" working, which is thrilling!
Unfortunately, a more complex application, busybox, which uses bsearch
and thus a callback function, fails because GCC loads the address for
the callback function using a GOTOFF32 relocation. In the XIP case
where .text and .data are separated and .got does not immediately
follow .text, a GOTOFF32 relocation to a symbol in the .text segment
is super broken.
bc84: 4b05 ldr r3, [pc, #20] (bc9c <.text+0xbc9c>)
bc86: b081 sub sp, #4
bc88: 4453 add r3, sl
bc8a: 9300 str r3, [sp, #0]
...
bc9c: 2461 movs r4, #97
bc9c: R_ARM_GOTOFF32 applet_name_compare
Loading the address of the callback function with either a PC relative
relocation or a GOT (not GOTOFF) relocation would work. Can I prevent
GCC from using GOTOFF32 relocations to symbols located in the .text
segment?
Can someone on the list verify with their toolchain that the address
of a static function is loaded using a GOTOFF32 relocation? The
following test should suffice. It's interesting to note that if the
callback function is not static, GCC will use a GOT32 relocation
instead, which will work.
I'm using binutils 2.17 and gcc 4.1.1.
Cheers,
Shaun
$ cat f.c
void g(void (*h)(void)) {}
static void f(void) { g(f); }
$ arm-elf-gcc -mthumb -fPIC -msingle-pic-base -c f.c
$ arm-elf-objdump -rS f.o | tail -3
24: 0000 lsls r0, r0, #0
24: R_ARM_GOTOFF32 f
...
