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

[joe.s+bugzilla at somniumtech dot com]

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

Joe Seymour <joe.s+bugzilla at somniumtech dot com> changed:

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--- Comment #1 from Joe Seymour <joe.s+bugzilla at somniumtech dot com> ---
The test case provided in the initial report requires the
msp430-gcc-support-files (headers and linker scripts) provided by TI.

I believe the issue being described is that when you provide an interrupt
attribute that specifies the name/number of the interrupt, the compiler
generates a section named "__interrupt_vector_<number>" containing the
address of the function. It expects the linker script to use these
sections to construct the vector table.

The linker doesn't know that these sections are related to specific
functions, so it doesn't know to discard the section corresponding to the
weak version of the function when it discards the weak function.

IIUC while making the sections comdat will ensure that all but one of
them is discarded, the section it keeps won't necessarily correspond to
the version of the function that was kept, so the resulting vector table
may be incorrect in some cases.

A workaround might be to to use /DISCARD/ in a linker script, to
explicitly discard the versions of the section that you don't want.
Alternatively, it might be easier and cleaner to omit the name/number of
the interrupt, so that the compiler doesn't generate a section, then
populate the vector table explicitly.

Both workarounds however require you to explicitly tell the linker which
version of the function is being used, at which point there might not be
any benefit to using the weak attribute.

Perhaps the msp430 backend should produce an error if a function is
marked and weak and specifies a particular interrupt number (instead of
just "interrupt")?  I'll submit a patch to gcc-patches.