http://sourceware.org/bugzilla/show_bug.cgi?id=15628
Bug ID: 15628
Summary: Cortex M4 incorrect blx instruction generated
Product: binutils
Version: 2.24 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: matti at henttunen dot se
It seems incorrect code is generated when I compile the following example
-------mylib.c-----------
int test()
{
return 1;
}
arm-none-eabi-gcc -fPIC -mcpu=cortex-m4 -mthumb -O2 -ggdb mylib.c -o mylib.so
arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -O2 -ggdb -lmylib main.c -o test
----main.c---------
int main()
{
test();
return 1;
}
The machine generated code for main looks as follows (objdump -D):
0000015c <main>:
15c: b508 push {r3, lr}
15e: f000 e888 blx 270 <__libc_fini_array+0xfc>
162: 2001 movs r0, #1
164: bd08 pop {r3, pc}
166: bf00 nop
instruction at 15e: seems incorrect to me, since M4 only branches using
a register blx{cond} Rm, (M3 seems to be ok with label aswell.)
Ive tried to use -mlong-calls, and it produces:
00000164 <main>:
164: b508 push {r3, lr}
166: f240 237c movw r3, #636 ; 0x27c
16a: f2c0 0300 movt r3, #0
16e: 4798 blx r3
170: 2001 movs r0, #1
172: bd08 pop {r3, pc}
This looks OK except for the address in R3 not being rellative, since it's
absolute it's not correct either (or am I missing something)
is a workaround for this, or am I doing something wrong here ?
/Matias
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