Re: [PATCH v1 05/10] gdb: introduce helper class file_reader_t

[Matthieu Longo <matthieu.longo@arm.com>]

On 10/07/2026 22:43, Kevin Buettner wrote:
> On Tue, 7 Jul 2026 16:48:55 +0100
> Matthieu Longo <matthieu.longo@arm.com> wrote:
> 
>> diff --git a/gdb/target.h b/gdb/target.h
>> index 4215553033c..d6fc101f205 100644
>> --- a/gdb/target.h
>> +++ b/gdb/target.h
>> @@ -2338,6 +2338,71 @@ extern LONGEST target_fileio_read_alloc (struct inferior *inf,
>>  extern gdb::unique_xmalloc_ptr<char> target_fileio_read_stralloc
>>      (struct inferior *inf, const char *filename, size_t *len = nullptr);
>>  
>> +/* Helper class for reading a file.  */
>> +template <typename T>
>> +class file_reader_t
>> +{
>> +  /* The filepath of the file being read.  */
>> +  std::string m_filepath;
>> +  /* Smart pointer to the data.  */
>> +  gdb::unique_xmalloc_ptr<T> m_data;
>> +  /* Size of the data.  */
>> +  size_t m_size;
>> +
>> +public:
>> +  file_reader_t (const std::string &filepath)
>> +    : m_filepath (filepath)
>> +    , m_size (0)
>> +  {
>> +    if constexpr (std::is_same_v<T, char>)
>> +      m_data = target_fileio_read_stralloc (nullptr, m_filepath.c_str (),
>> +					    &m_size);
>> +    else
>> +      {
>> +	gdb_byte *buf = nullptr;
>> +	m_size = target_fileio_read_alloc (nullptr, m_filepath.c_str (), &buf);
> 
> m_size is a size_t, which is unsigned.  But target_fileio_read_alloc
> returns a signed value and if it fails, the return value will be -1,
> right?  I think you need to handle this case somehow...
> 
> Kevin
> 

Given that you raise this question, it makes me question whether the semantic of
target_fileio_read_stralloc is not misleading.

target_fileio_read_stralloc always returns a positive value.
A size of 0 is set when an issue occurs.
An error can be detected when checking the returned value for nullptr. Setting the size to -1 is
superfluous.
Hence this method in file_reader_t to check whether the object is valid.

  /* Return true if the file was read successfully.  */
  operator bool () const noexcept
  { return m_data != nullptr && m_size > 0; }

Note that an empty file would means that m_data is not null, but its size would be 0.
I decided to treat both of them in the same way because we cannot do much with an empty procfs file.

Matthieu