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Re: ARM mapping symbols and --strip-unneeded
- From: Nick Clifton <nickc at redhat dot com>
- To: "Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>, Michael Weiser <michael at weiser dot dinsnail dot net>
- Cc: binutils at sourceware dot org
- Date: Wed, 29 Jun 2016 10:24:48 +0100
- Subject: Re: ARM mapping symbols and --strip-unneeded
- Authentication-results: sourceware.org; auth=none
- References: <20160626221336 dot GB1916 at weiser dot dinsnail dot net> <e7fff803-6244-4782-2768-6b301387aed8 at redhat dot com> <577132D2 dot 9090903 at arm dot com> <1aa007dc-68eb-2d6f-d731-561564a1e3da at redhat dot com> <5772A892 dot 2000208 at arm dot com>
> Might be safer to use strncmp (sym, type, 2) since 'extended' mapping
> symbols can be produced by some tools.
We might as well extract mapping symbol determination into a separate
function - I have a feeling that it is going to be needed again in the
future. So what do you think of this patch ?
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 04e776c..105e3cc 100644
@@ -18266,6 +18266,28 @@ elf32_arm_copy_special_section_fields (const bfd *ibfd ATTRIBUTE_UNUSED,
+/* Returns TRUE if NAME is an ARM mapping symbol.
+ Traditionally the symbols $a, $d and $t have been used.
+ The ARM ELF standard also defines $x (for A64 code). It also allows a
+ period initiated suffix to be added to the symbol: "$[adtx]\.[:sym_char]+".
+ Other tools might also produce $b (Thumb BL), $f, $p, $m and $v, but we do
+ not support them here. $t.x indicates the start of ThumbEE instructions. */
+is_mapping_symbol (const char * name)
+ return name != NULL /* Paranoia. */
+ && name == '$' /* Note: if objcopy --prefix-symbols has been used then
+ the mapping symbols could have acquired a prefix.
+ We do not support this here, since such symbols no
+ longer conform to the ARM ELF ABI. */
+ && (name == 'a' || name == 'd' || name == 't' || name == 'x')
+ && (name == 0 || name == '.');
+ /* FIXME: Strictly speaking the symbol is only a valid mapping symbol if
+ any characters that follow the period are legal characters for the body
+ of a symbol's name. For now we just assume that this is the case. */
/* Make sure that mapping symbols in object files are not removed via the
"strip --strip-unneeded" tool. These symbols are needed in order to
correctly generate interworking veneers, and for byte swapping code
@@ -18276,11 +18298,8 @@ static void
elf32_arm_backend_symbol_processing (bfd *abfd, asymbol *sym)
if (((abfd->flags & (EXEC_P | DYNAMIC)) == 0)
- && sym->name != NULL
&& sym->section != bfd_abs_section_ptr
- && (strcmp (sym->name, "$a") == 0
- || strcmp (sym->name, "$t") == 0
- || strcmp (sym->name, "$d") == 0))
+ && is_mapping_symbol (sym->name))
sym->flags |= BSF_KEEP;