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Re: ARM mapping symbols and --strip-unneeded
- From: "Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>
- To: Andrew Pinski <pinskia at gmail dot com>, Nick Clifton <nickc at redhat dot com>
- Cc: Michael Weiser <michael at weiser dot dinsnail dot net>, binutils <binutils at sourceware dot org>
- Date: Wed, 29 Jun 2016 10:41:07 +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> <b24a6c7e-f657-9529-e27a-de61604cabd2 at redhat dot com> <CA+=Sn1mEsufHh=QVoLyznMDJ9T7wg_4WpbWVhWv7YNyc+zOtXw at mail dot gmail dot com>
On 29/06/16 10:26, Andrew Pinski wrote:
> On Wed, Jun 29, 2016 at 2:24 AM, Nick Clifton <nickc@redhat.com> wrote:
>> Hi Richard,
>>
>>> 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 ?
>
> We should check aarch64 target as it might have the same issue too as
> it uses $d and $t too.
>
Although AArch64 ELF defines some mapping symbols, I don't think they
are currently needed beyond being helpers for disassembly (code vs data).
R.
> Thanks,
> Andrew
>
>>
>> Cheers
>> Nick
>>
>> diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
>> index 04e776c..105e3cc 100644
>> --- a/bfd/elf32-arm.c
>> +++ b/bfd/elf32-arm.c
>> @@ -18266,6 +18266,28 @@ elf32_arm_copy_special_section_fields (const bfd *ibfd ATTRIBUTE_UNUSED,
>> return FALSE;
>> }
>>
>> +/* 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. $t.x indicates the start of ThumbEE instructions. */
>> +
>> +static bfd_boolean
>> +is_mapping_symbol (const char * name)
>> +{
>> + return name != NULL /* Paranoia. */
>> + && name[0] == '$' /* 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[1] == 'a' || name[1] == 'd' || name[1] == 't' || name[1] == 'x')
>> + && (name[2] == 0 || name[2] == '.');
>> + /* 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;
>> }