[fpc-devel] Proposal: Supporting initial references for weakexternal
jepjoh2 at es.aau.dk
Wed Jan 12 19:16:27 CET 2011
Den 12-01-2011 12:42, Jonas Maebe skrev:
> On 12 Jan 2011, at 06:29, Jeppe Johansen wrote:
>> While trying to find a nice solution for generating interrupt vector
>> tables on ARM, I found that the usually employed solution is to
>> generate weak references to symbols, that are initialized to a single
>> handler. This way an application can override the weak reference, by
>> declaring a new symbol with the same name. While it's possible to do
>> that currently by using some external assembler code, I think a
>> simpler solution could be made by using the weakexternal directive.
>> The infrastructure is already there, but it's used in a slightly
>> different way.
> How is it normally done in C? At first sight, using the weakexternal
> directive to /define/ symbols seems like a wrong approach.
With C it's done using compiler dependent attributes. With gcc you can
do it using __attribute__((weak,alias("SomeFunction")));. Though often
it'll just be done using assembler using the .weak and .set/thumb_set
The weakexternal directive already "defines" a symbol, it will exist at
runtime, but it might be nil. The only difference is that if you set the
initial value it'll resolve to something at link time
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