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Re: [PATCH] symbols: discard stray file symbols
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Thu, 4 Sep 2025 17:53:14 -0400
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, 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, 04 Sep 2025 21:53:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-04-16 05:00, Jan Beulich wrote:
By observation GNU ld 2.25 may emit file symbols for .data.read_mostly
when linking xen.efi. Due to the nature of file symbols in COFF symbol
tables (see the code comment) the symbols_offsets[] entries for such
symbols would cause assembler warnings regarding value truncation. Of
course the resulting entries would also be both meaningless and useless.
Add a heuristic to get rid of them, really taking effect only when
--all-symbols is specified (otherwise these symbols are discarded
anyway).
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Factor 2 may in principle still be too small: We zap what looks like
real file symbols already in read_symbol(), so table_cnt doesn't really
reflect the number of symbol table entries encountered. It has proven to
work for me in practice though, with still some leeway left.
--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -213,6 +213,16 @@ static int symbol_valid(struct sym_entry
if (strstr((char *)s->sym + offset, "_compiled."))
return 0;
+ /* At least GNU ld 2.25 may emit bogus file symbols referencing a
+ * section name while linking xen.efi. In COFF symbol tables the
+ * "value" of file symbols is a link (symbol table index) to the next
+ * file symbol. Since file (and other) symbols (can) come with one
+ * (or in principle more) auxiliary symbol table entries, the value in
+ * this heuristic is bounded to twice the number of symbols we have
+ * found. See also read_symbol() as to the '?' checked for here. */
+ if (s->sym[0] == '?' && s->sym[1] == '.' && s->addr < table_cnt * 2)
+ return 0;
+
return 1;
}
I looked at this. It'll drop symbols, but I don't know enough to give
an R-b. I can't give an actionable A-b either. Maybe someone else can
chime in.
Maybe this is just showing my lack of knowledge, but could any symbol
starting "?." be considered invalid? I don't think I've ever seen any
like that.
Regards,
Jason
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