On Mon, Aug 07, 2017 at 04:11:43PM +0100, Dibyendu Majumdar wrote:
> Hi,
>
> I would like to understand the structure of the parse tree generated
> by Sparse a bit better. I am looking at the output from the show_*()
> functions but it is not clear to me exactly what the output means. For
> example:
>
> extern int printf(const char *, ...);
>
> int main(int argc, const char *argv[]) {
> printf("hello world!\n");
> return 0;
> }
>
> Results in:
>
> .align 4
> int extern [signed] [addressable] [toplevel] main( ... )
> movi.64 v2,&"hello world!\n"
> push.64 v2
> call printf
> add.64 vSP,vSP,$8
> mov.32 v3,retval
> movi.32 v4,$0
> addi.64 v5,vFP,$offsetof(return:00000202755B1A98)
> st.32 v4,[v5]
> ret (00000202755B1A98)
> .L00000202755B1A98:
> addi.64 v6,vFP,$offsetof(return:00000202755B1A98)
> ld.32 v7,[v6]
> mov.32 retval,7
> ret
>
>
> I get the first four lines, but the rest don't make sense to me.
The 'vFP' is the (virtual) Frame Pointer and the $offsetof() is
the offset to where the variable is stored in the frame.
'retval' seems to be a pseudo-register used for the return value
of function calls and 'return' seems to be a pseudo-variable holding
the return value.
So v3 hold the return value of the printf() (and is ignored) then
0 is stored in the 'return' pseudo-variable and is read-back just
after to be returned by the function.
> I suppose that the dump is trying to show the parse tree in a linear
> form ... but is that useful? Would it be better to dump the parse
> tree in a different form?
Yes, I think so too.
I only tried it a few time and it wasn't at all helping me.
The parsing tree is all about the statements and the expressions,
so I always end to look directly at the code.
I dunno about the inspect & dissect tools.
-- Luc
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