Hi Guo Ren:
In C language, your conclusion is correct, but in assembly language,
global_symbol != &global_symbol
I did the following experiment:
liyang@liyang-virtual-machine:~/Desktop/test$ ls
main.c test.s
liyang@liyang-virtual-machine:~/Desktop/test$ cat test.s
.globl test_symbol
test_symbol:
nop
liyang@liyang-virtual-machine:~/Desktop/test$ cat main.c
#include <stdio.h>
extern unsigned long test_symbol;
int main(void)
{
printf("test_symbol = 0x%lx\n",(unsigned long)test_symbol);
printf("&test_symbol = 0x%lx\n",(unsigned long)&test_symbol);
printf("main = 0x%lx\n",(unsigned long)main);
printf("&main = 0x%lx\n",(unsigned long)&main);
}
liyang@liyang-virtual-machine:~/Desktop/test$ gcc main.c test.s --static -o test
liyang@liyang-virtual-machine:~/Desktop/test$ ls
main.c test test.s
liyang@liyang-virtual-machine:~/Desktop/test$ readelf test -s | grep test_symbol
884: 000000000040170c 0 NOTYPE GLOBAL DEFAULT 7 test_symbol
liyang@liyang-virtual-machine:~/Desktop/test$ readelf test -s | grep main -w
1605: 0000000000401685 135 FUNC GLOBAL DEFAULT 7 main
liyang@liyang-virtual-machine:~/Desktop/test$ ./test
test_symbol = 0x4b853001f0f90
&test_symbol = 0x40170c
main = 0x401685
&main = 0x401685
The above test can lead to the conclusion that:
Both c_symbol and &c_symbol represent the address of a symbol, but
&ASM_symbol represents the address of a symbol while ASM_symbol
represents the opcode stored at that address.
On Thu, Oct 17, 2024 at 2:05 PM Guo Ren <guoren@xxxxxxxxxx> wrote:
>
> On Wed, Oct 16, 2024 at 5:56 PM Yang Li <yang.li85200@xxxxxxxxx> wrote:
> >
> > In the csky_cmpxchg_fixup function, it is incorrect to use the global
> > variable csky_cmpxchg_stw to determine the address where the exception
> > occurred.The global variable csky_cmpxchg_stw stores the opcode at the
> > time of the exception, while &csky_cmpxchg_stw shows the address where
> > the exception occurred.
> >
> > Signed-off-by: Yang Li <yang.li85200@xxxxxxxxx>
> > ---
> > V1 -> V2:Eliminate compilation warnings
> >
> > arch/csky/mm/fault.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/csky/mm/fault.c b/arch/csky/mm/fault.c
> > index a885518ce1dd..5226bc08c336 100644
> > --- a/arch/csky/mm/fault.c
> > +++ b/arch/csky/mm/fault.c
> > @@ -45,8 +45,8 @@ static inline void csky_cmpxchg_fixup(struct pt_regs *regs)
> > if (trap_no(regs) != VEC_TLBMODIFIED)
> > return;
> >
> > - if (instruction_pointer(regs) == csky_cmpxchg_stw)
> > - instruction_pointer_set(regs, csky_cmpxchg_ldw);
> > + if (instruction_pointer(regs) == (unsigned long)&csky_cmpxchg_stw)
> > + instruction_pointer_set(regs, (unsigned long)&csky_cmpxchg_ldw);
> csky_cmpxchg_ldw(stw) is a label symbol, not a variable.
>
> arch/csky/kernel/atomic.S:
> GLOBAL(csky_cmpxchg_ldw)
> GLOBAL(csky_cmpxchg_stw)
>
> Your modification does not affect the ASM output.
>
> (gdb) p main
> $1 = {void (void)} 0x5fa <main>
> (gdb) p &main
> $2 = (void (*)(void)) 0x5fa <main>
>
> > return;
> > }
> > #endif
> > --
> > 2.34.1
> >
>
>
> --
> Best Regards
> Guo Ren
