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Re: [PATCH 5/6] symbols: arrange to know where functions end
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 13 Mar 2025 16:39:37 +0000
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- Cc: Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 13 Mar 2025 16:42:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13/03/2025 1:54 pm, Jan Beulich wrote:
> When determining the symbol for a given address (e.g. for the %pS
> logging format specifier), so far the size of a symbol (function) was
> assumed to be everything until the next symbol. There may be gaps
> though, which would better be recognizable in output (often suggesting
> something odd is going on).
Do you have an example %pS for this new case?
> Insert "fake" end symbols in the address table, accompanied by zero-
> length type/name entries (to keep lookup reasonably close to how it
> was).
>
> Note however that this, with present GNU binutils, won't work for
> xen.efi: The linker loses function sizes (they're not part of a normal
> symbol table entry), and hence nm has no way of reporting them.
By "present GNU binutils", does this mean that you've got a fix in mind
(or in progress), or that it's an open problem to be solved?
> The address table growth is quite significant on x86 release builds (due
> to functions being aligned to 16-byte boundaries), though: Its size
> almost doubles.
Why does the function alignment affect the growth?
> Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Note: Style-wise this is a horrible mix. I'm trying to match styles with
> what's used in the respective functions.
>
> Older GNU ld retains section symbols, which nm then also lists. Should
> we perhaps strip those as we read in nm's output? They don't provide any
> useful extra information, as our linker scripts add section start
> symbols anyway. (For the purposes here, luckily such section symbols are
> at least emitted without size.)
Will symbols_lookup() ever produce these? If not, it might be better to
ignore the problem.
Taking extra logic to work around a benign issue in older toolchains
isn't necessarily ideal.
~Andrew
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