linux-kernel - Re: [PATCH v4 3/7] fs/procfs: add build ID fetching to PROCMAP

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Message-ID: <uofb56lk6isrwqf42ilky7r3wa4tetaaze2m2ususzqpbnftkw@hwskh5quvlfm>
Date: Wed, 12 Jun 2024 14:28:09 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, brauner@...nel.org, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, gregkh@...uxfoundation.org, linux-mm@...ck.org,
        surenb@...gle.com, rppt@...nel.org, gerd.rausch@...cle.com
Subject: Re: [PATCH v4 3/7] fs/procfs: add build ID fetching to PROCMAP_QUERY
 API

* Andrii Nakryiko <andrii@...nel.org> [240611 07:01]:
> The need to get ELF build ID reliably is an important aspect when
> dealing with profiling and stack trace symbolization, and
> /proc/<pid>/maps textual representation doesn't help with this.
> 
> To get backing file's ELF build ID, application has to first resolve
> VMA, then use it's start/end address range to follow a special
> /proc/<pid>/map_files/<start>-<end> symlink to open the ELF file (this
> is necessary because backing file might have been removed from the disk
> or was already replaced with another binary in the same file path.

Can we please also add the vma_kernel_pagesize() to this interface?  We
have a user who parses the entire smaps file specifically for
KernelPageSize, which could be included for a low cost here.

The only way to get this information today seems to be from the
/proc/<pid>/smaps file and it is necessary for certain hugepage calls
for alignment reasons (otherwise the calls fail with -EINVAL).  Adding
this extra information would allow for another text-parsing user to
switch to this API.

Thanks,
Liam