Re: [PATCH][PR sanitizer/77631] Support separate debug info in libbacktrace

["Ian Lance Taylor via gcc-patches" <gcc-patches at gcc dot gnu dot org>]

On Tue, Mar 14, 2017 at 7:30 AM, Denis Khalikov
<d.khalikov@partner.samsung.com> wrote:
> Thanks for review, got all of my mistakes, except one.
>
>
>> -      descriptor = backtrace_open (info->dlpi_name, pd->error_callback,
>> -   pd->data, &does_not_exist);
>> +      descriptor
>> + = backtrace_open_debugfile (info->dlpi_name, pd->error_callback,
>> pd->data,
>> +    &debugfile_does_not_exist, pd->state, 0);
>> +      if (descriptor < 0)
>> +  descriptor = backtrace_open (info->dlpi_name, pd->error_callback,
>> +       pd->data, &does_not_exist);
>
> This seems like unnecessary work.  Shouldn't we only try to open the
> debug file if we find a .gnu_debuglink section?
>
> Should i move code below
>
>   /* check if debug section does exist */
>  debug_link_data
>     = elf_gnu_debuglink_section (state, descriptor, error_callbackdata, exe,
> &debug_link_data_len);
>
> from backtrace_open_debugfile .

As far as I know all the debuglink code is ELF-specific.  I would do
it all in elf.c.  While reading the sections of the executable, look
for a debuglink section, and use it if present.  Keep the readlink
code in posix.c, I suppose.  Apologies if this doesn't make sense.

Ian



> On 03/14/2017 04:49 PM, Ian Lance Taylor wrote:
>>
>> On Mon, Mar 13, 2017 at 10:16 AM, Denis Khalikov
>> <d.khalikov@partner.samsung.com> wrote:
>>>
>>> Hello everyone, i have a patch for this issue.
>>>
>>> List of implemented functionality:
>>>
>>> 1.Reading .gnu_debuglink section from ELF file:
>>>  a. Reading name of debug info file.
>>>  b. Verifying crc32 sum.
>>>
>>> 2. Searching for separate debug info file from paths:
>>>  a. /usr/lib/debug/path/to/executable
>>>  b. /path/to/executable
>>>  c. /path/to/executable/.debug
>>>
>>> Assumed that debug info file generated by objcopy from binutils.
>>>
>>> objcopy --only-keep-debug foo foo.debug
>>> strip -g foo
>>> objcopy --add-gnu-debuglink=foo.debug foo
>>
>>
>>> +clean_separate:glinktest.debug
>>> + rm -f glinktest.debug
>>> +
>>> +separate: glinktest
>>> + if test -n "$(OBJCOPY)" &&  test -n "$(STRIP)";  \
>>> + then \
>>> + $(OBJCOPY) --only-keep-debug glinktest glinktest.debug;\
>>> + $(STRIP) glinktest;\
>>> + $(OBJCOPY) --add-gnu-debuglink=glinktest.debug glinktest;\
>>> + fi;
>>
>>
>> As far as I know "separate" is not a special thing in automake.  We
>> should always run (and clean) this test if the necessary objcopy
>> option is available.
>>
>>> +glinktest.lo: (INCDIR)/filenames.h backtrace.h backtrace-supported.h
>>
>>
>> Missing '$'  in "$(INCDIR)".
>>
>>> +/* Return 1 if header is valid and -1 on fail */
>>
>>
>> This comment does not explain what the function actually does.
>>
>>> +/* Return the pointer to char array with data from .gnudebuglink section
>>> inside.  */
>>
>>
>> Line too long, we use 80 column lines.
>>
>>> +unsigned char *
>>> +elf_gnu_debuglink_section (struct backtrace_state *state, int
>>> descriptor,
>>> +   backtrace_error_callback error_callback, void *data,
>>> +   int exe, int *gnulink_data_len_out)
>>
>>
>> This should be static.  I see that you are calling it elsewhere, but
>> it doesn't make sense to call an "elf" function outside of elf.c.
>> This library is used on non-ELF systems.
>>
>>> +  /* Look for for the .gnu_debuglink section  */
>>
>>
>> Period at end of sentence.
>>
>>>    /* To translate PC to file/line when using DWARF, we need to find
>>> -     the .debug_info and .debug_line sections.  */
>>> +   the .debug_info and .debug_line sections.  */
>>
>>
>> Why change the indentation like this?  I think the original was correct.
>>
>>> -      descriptor = backtrace_open (info->dlpi_name, pd->error_callback,
>>> -   pd->data, &does_not_exist);
>>> +      descriptor
>>> + = backtrace_open_debugfile (info->dlpi_name, pd->error_callback,
>>> pd->data,
>>> +    &debugfile_does_not_exist, pd->state, 0);
>>> +      if (descriptor < 0)
>>> +  descriptor = backtrace_open (info->dlpi_name, pd->error_callback,
>>> +       pd->data, &does_not_exist);
>>
>>
>> This seems like unnecessary work.  Shouldn't we only try to open the
>> debug file if we find a .gnu_debuglink section?
>>
>>> +/*Just a simple test copied from btest.c, but in this case we don't have
>>> debug
>>> + * info in the executable and test should verify that we can read debug
>>> info
>>> + * from separate file. See Makefile check-TESTS target. */
>>
>>
>> No leading '*' on subsequent lines of multi-line comments, see existing
>> code.
>>
>> I'm not sure I see the point of glinktest.c.  Why don't we just use
>> btest.c?
>>
>>> +#define MAX_PATH_LEN 4096 /*  from linux/limits.h   */
>>
>>
>> This library works on systems other than GNU/Linux.  We should
>> dynamically allocate the buffer.
>>
>>> +  while (len > 1 && !IS_DIR_SEPARATOR (*(buffer + (len - 1))))
>>
>>
>> while (len > 1 && !IS_DIR_SEPARATOR(buffer[len-1]))
>>
>> or just call basename.  I'm not sure why you bother with the count
>> variable; doesn't full_filename_len - count exactly == len?
>>
>>> +  sign_byte = 0x00;
>>> +  count = 0;
>>> +  while (*(buffer + count) != sign_byte && size > count)
>>> +    ++count;
>>> +  return count;
>>
>>
>> This looks like `return strnlen(buffer, size)`.
>>
>> Ian
>>
>>
>>
>