-finline and ISRs - ReadList.com

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-finline and ISRs
\ Edwin Olson (21 Apr 2007)
. \ Daniel Lohmann (23 Apr 2007)

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Subject:	-finline and ISRs
Group:	Gcc-help
From:	Edwin Olson
Date:	21 Apr 2007

I'm working with a small embedded O/S on an ARM7TDMI.

A typical IRQ handler must save the state of a previous task, perform
some processing, possibly invoke the scheduler, and then restore a new
task. I'd like to do as much of this as possible from C, but
automatically generated prologue/epilogue chunks interfere with my
IRQ_TASK_SAVE/RESTORE macros (which are inline assembly). So I've been
doing this:

static void emac_irq(void) __attribute__ ((naked));
static void emac_irq(void)
{
IRQ_TASK_SAVE;
emac_irq_real();
IRQ_TASK_RESTORE;
}

Calling out to the actual ISR as a separate function call seems to
isolate stack variable allocations to the section between the
IRQ_TASK_SAVE/RESTORE.

This works pretty well, however, if I optimize at -O4, emac_irq_real is
inlined, and the IRQ handler no longer runs correctly. (I've verified:
the code works with -O4 -fno-inline, but doesn't work with just -O4).

I can attach a "noinline" attribute to emac_irq_real, which again causes
things to work, but the whole thing is starting to feel clumsy.

Does anyone have an idea of how I can do this in a more elegant way,
that doesn't require setting a bunch of attributes?

-Ed