Hi!
I found a serious bug in the assembler macros in asm-mips/uaccess.h. They
all do something like that:
__asm__ __volatile__( \
"move\t$4, %1\n\t" \
"move\t$5, %2\n\t" \
"move\t$6, %3\n\t" \
".set\tnoreorder\n\t" \
__MODULE_JAL(__copy_user) \
...
The problem is that you cannot assume that gcc will not put %1, %2 or %3
in registers different from $4, $5 or $6. For example, if %2 is put in $4,
the code is incorrect. (With gcc-2.95.2 I got a bug in
generic_file_write!).
Did someone already fixed this bug ?
A possible fix would be to use asm registers:
#define copy_from_user(to,from,n) ({ \
register void *__cu_to asm("$4"); \
register const void *__cu_from asm("$5"); \
register long __cu_len asm("$6"); \
\
__cu_to = (to); \
__cu_from = (from); \
__cu_len = (n); \
if (access_ok(VERIFY_READ, __cu_from, __cu_len)) \
__asm__ __volatile__( \
".set\tnoreorder\n\t" \
__MODULE_JAL(__copy_user) \
...
But I am not sure that it is always correct. Any idea ?
Fabrice.
