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Re: [avr-gcc-list] Function Address fixup missing?

From: Maurizio Ferraris Studio
Subject: Re: [avr-gcc-list] Function Address fixup missing?
Date: Fri, 26 Jun 2009 18:36:38 +0200
User-agent: Thunderbird (Windows/20090605)

Stu Bell wrote:
> Trampolines work only for statically linked functions, not function
> pointers.
Sorry, but I don't understand this.
I believe that there is no problem with statically linked functions.
GCC actually generates a call with the full address, and no 16 bit
pointers are involved, as in the following disassembly:

    butta = ButtamiViaSubito();
    4014:       0f 94 f5 06     call    0x20dea ; 0x20dea

Here I am calling the same function but directly, and GCC generates the
correct code for the AtMega2561.

Actually, as I told in my previous mail, I tried a small program
where it seems to work.

Here is the main:
    typedef void (*PPro)(void);
    PPro ppro1;

    extern void pro1(void) __attribute__ ((section ("spro1")));

    int main(void)
      ppro1 = pro1;



Here is the function:
    __attribute__((section ("spro1"))) void pro1(void)

In the linker flags I added:
to place the routine in the upper 128K.

and the relevant disassembly is:
000000cc <__trampolines_start>:
  cc:   0d 94 00 08     jmp     0x21000 ; 0x21000 <pro1>
  ppro1 = pro1;
 116:   86 e6           ldi     r24, 0x66       ; 102
 118:   90 e0           ldi     r25, 0x00       ; 0
 11a:   90 93 01 02     sts     0x0201, r25
 11e:   80 93 00 02     sts     0x0200, r24
 126:   e0 91 00 02     lds     r30, 0x0200
 12a:   f0 91 01 02     lds     r31, 0x0201
 12e:   19 95           eicall

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