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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/98482] -mfentry creates invalid call for -mcmodel=large
Date: Fri, 08 Jan 2021 14:50:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98482

--- Comment #14 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #10)
> If we are emitting for nested functions
> 	pushq	%r10
> 1:	call	__fentry__
> 	popq	%r10
> (is it ok to misalign the stack for __fentry__? but then even plain call
> __fentry__ actually misaligns it), then perhaps we can do similarly for t=
he
> PIC case.  But I wonder how does __fentry__ then find the caller if it ca=
n't
> rely on the return address being right above the return address to the
> function that called __fentry__ (appart from unwind info of course, but we
> don't really emit .cfi_* directives here either, do we?).

Generic part of the compiler pushes static chain register for nested functi=
ons,
so there is little we can do in the target part. If there is a problem with
misaligned stack, then I think __mcount_internal will have to be realigned,
because calls to both, mcount and __fentry__ can be misaligned.

I don't know what to do with __fentry__ argument. Luckily, mcount finds its
argument via frame pointer, so it works there.=