[Bug target/70713] New: msp430 interrupt attribute prevents overriding weak symbols

[awygle at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70713

            Bug ID: 70713
           Summary: msp430 interrupt attribute prevents overriding weak
                    symbols
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: awygle at gmail dot com
  Target Milestone: ---

Because the interrupt attribute in the msp430 port creates a .word directive
inside of the generated assembly, thus:

test.c:
__attribute__((weak, interrupt(USCI_A1_VECTOR)))
  void TEST_WEAKNESS(void) {
    UCA1TXBUF = 'e';
  }

msp430-elf-gcc -mmcu=msp430fr6989 -S test.c

test.s:
  .file "test.c"
.text
  .balign 2
  .weak TEST_WEAKNESS
  .section  __interrupt_vector_43,"ax",@progbits
  .word TEST_WEAKNESS
  .text
TEST_WEAKNESS:
; start of function
; attributes: interrupt
; framesize_regs:     0
; framesize_locals:   0
; framesize_outgoing: 0
; framesize:          0
; elim ap -> fp       2
; elim fp -> sp       0
; saved regs:(none)
  ; start of prologue
  ; end of prologue
  MOV.W #101, &UCA1TXBUF
  NOP
  ; start of epilogue
  RETI
  .size TEST_WEAKNESS, .-TEST_WEAKNESS


When we compile and attempt to link with a non-weak symbol, thus:

test2.c:
__attribute__((interrupt(USCI_A1_VECTOR)))
  void TEST_WEAKNESS(void) {
    UCA1TXBUF = 'E';
  }

msp430-elf-gcc -mmcu=msp430fr6989 -S test2.c

test2.s:
  .file "test2.c"
.text
  .balign 2
  .global TEST_WEAKNESS
  .section  __interrupt_vector_43,"ax",@progbits
  .word TEST_WEAKNESS
  .text
TEST_WEAKNESS:
; start of function
; attributes: interrupt
; framesize_regs:     0
; framesize_locals:   0
; framesize_outgoing: 0
; framesize:          0
; elim ap -> fp       2
; elim fp -> sp       0
; saved regs:(none)
  ; start of prologue
  ; end of prologue
  MOV.W #69, &UCA1TXBUF
  NOP
  ; start of epilogue
  RETI
  .size TEST_WEAKNESS, .-TEST_WEAKNESS

The error:
msp430-elf-gcc -mmcu=msp430fr6989 test.s test2.s -o test.elf
msp430-elf/bin/ld: test.elf section `__interrupt_vector_43' will not fit in
region `VECT43'
msp430-elf/bin/ld: region `VECT43' overflowed by 2 bytes
collect2: error: ld returned 1 exit status


I was able to get this to work by making the section lines part of a comdat
group, so that
  .section  __interrupt_vector_43,"ax",@progbits
becomes
  .section  __interrupt_vector_43,"axG",@progbits,TEST_WEAKNESS,comdat
in both cases. There seem to be no ill-effects from doing this (provided the
group name is based on the function name), but I lack the gcc experience to say
for sure, or to cause such code to be emitted.