[PATCH] ARM: TCM memory bug on newer compilers
Russell King - ARM Linux
linux at arm.linux.org.uk
Tue May 25 16:16:32 EDT 2010
On Tue, May 25, 2010 at 06:45:47PM +0200, Linus Walleij wrote:
> Apparently newer compilers don't like you to refer to linker
> symbols as extern char *foo, we must use char foo and refer to
> the address of the char instead.
afaik, that's always been the case.
Let's take an example. Location 0x1234 contains value 0x89abcdef.
The symbol __tcm_start has the address of 0x1234.
Now:
extern char *__tcm_start;
declares a pointer to a char. The address of the __tcm_start storage
will be 0x1234. The value of __tcm_start will be 0x89abcdef - and
this is the value that would be passed to __pa(__tcm_start). The
value of __tcm_start[0] is whatever is stored at the address
0x89abcdef.
extern char __tcm_start[];
declares an array of char. The address of the __tcm_start storage will
be 0x1234. The value of __tcm_start is in this case defined to be the
same as the value of a pointer to the first element - so 0x1234.
The value of __tcm_start[0] will be whatever is stored at 0x1234, and in
LE that will be 0xef.
extern char __tcm_start;
declares a single char. The address of the __tcm_start storage will be
0x1234. The value of __tcm_start is the value at this address, and
still assuming LE, 0xef.
So, either use:
extern char __tcm_start;
pa_start = __pa(&__tcm_start);
or:
extern char __tcm_start[];
pa_start = __pa(__tcm_start);
which reveal the same answer. However, this will give you something
completely different:
extern char *__tcm_start;
pa_start = __pa(__tcm_start);
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