Re: [PATCH] [gdb/tdep] Eliminate ostringstream use from arc_check_tdesc_feature

[Tom de Vries <tdevries@suse.de>]

On 3/22/26 3:41 PM, Simon Marchi wrote:
> On 3/22/26 2:58 AM, Tom de Vries wrote:
>> We generally avoid C++ streams in GDB sources [1].
>>
>> Remove an instance of std::ostringstream in arc_check_tdesc_feature.
>>
>> While we're at it, fix an array index bug:
>> ...
>> -		reg_names << " or '" << reg.names[0] << "'";
>> +		string_appendf (reg_names, " or '%s'", reg.names[i]);
>> ...
>>
>> Tested on x86_64-linux, using a trigger patch:
>> ...
>> -      if (!found && reg.required_p)
>> +      if (true || (!found && reg.required_p))
>> ...
>> and doing "maint selftest" and observing the output:
>> ...
>> Running selftest unpack_field_as_long::ARC600.
>> Error: Cannot find required register(s) 'r0' in feature 'org.gnu.gdb.arc.core'.
>> Error: Cannot find required register(s) 'pc' in feature 'org.gnu.gdb.arc.aux'.
>> ...
>>
>> [1] https://sourceware.org/pipermail/gdb-patches/2026-March/226117.html
>> ---
>>   gdb/arc-tdep.c | 9 ++++-----
>>   1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/gdb/arc-tdep.c b/gdb/arc-tdep.c
>> index ff283014e52..4936a5c8fbb 100644
>> --- a/gdb/arc-tdep.c
>> +++ b/gdb/arc-tdep.c
>> @@ -44,7 +44,6 @@
>>   
>>   /* Standard headers.  */
>>   #include <algorithm>
>> -#include <sstream>
>>   
>>   /* The frame unwind cache for ARC.  */
>>   
>> @@ -2100,16 +2099,16 @@ arc_check_tdesc_feature (struct tdesc_arch_data *tdesc_data,
>>   
>>         if (!found && reg.required_p)
>>   	{
>> -	  std::ostringstream reg_names;
>> +	  std::string reg_names;
>>   	  for (std::size_t i = 0; i < reg.names.size(); ++i)
>>   	    {
>>   	      if (i == 0)
>> -		reg_names << "'" << reg.names[0] << "'";
>> +		string_appendf (reg_names, "'%s'", reg.names[0]);
>>   	      else
>> -		reg_names << " or '" << reg.names[0] << "'";
>> +		string_appendf (reg_names, " or '%s'", reg.names[i]);
> 

Hi Simon,

thanks for the review.

> Looks like you fixed a bug here (0 -> i).

Yes, that's what I meant by "fix an array index bug".

Thanks,
- Tom

> Approved-By: Simon Marchi <simon.marchi@efficios.com>
> 
> Simon