On 11/12/20 4:30 PM, Andrii Nakryiko wrote:
On Thu, Nov 12, 2020 at 4:19 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
On Thu, Nov 12, 2020 at 4:08 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
So I looked at your vmlinux image. I think we should just keep
everything mostly as it it right now (without changes in this patch),
but add just two simple checks:
1. Skip if fn->declaration (ignore correctly marked func declarations)
2. Skip if DW_AT_inline: 1 (ignore inlined functions).
I'd keep the named arguments check as is, I think it's helpful. 1)
will skip stuff that's explicitly marked as declaration. 2) inline
check will partially mitigate dropping of fn->external check (and we
can't really attach to inlined functions).
I thought DW_AT_inline is an indication that the function was marked "inline"
in C code. That doesn't mean that the function was actually inlined.
So I don't think pahole should check that bit.
According to DWARF spec, there are 4 possible values:
DW_INL_not_inlined = 0 Not declared inline nor inlined by
the compiler
DW_INL_inlined = 1 Not declared inline but inlined by
the compiler
DW_INL_declared_not_inlined = 2 Declared inline but not inlined by
the compiler
DW_INL_declared_inlined = 3 Declared inline and inlined by the compiler
So DW_INL_inlined is supposed to be added to functions that are not
marked inline, but were nevertheless inlined. I saw this for one of
vfs_getattr entries in DWARF, which clearly is not marked inline.
I looked at llvm source code, llvm only tries to assign DW_INL_inlined
and also only at certain conditions. Not sure about gcc. Probably
similar. So this field is not reliable, esp. without it does not mean it
is not inlined.
But also that DWARF entry had proper args with names, so it would work
fine as well. I don't know, with DWARF it's always some guessing game.
Let's leave DW_AT_inline alone for now.
Important part is skipping declarations (when they are marked as
such), though I'm not claiming it will solve the problem completely...
:)
