[PATCH] RFC: come up with startswith function.

[Martin Liška]

On 4/20/21 1:43 PM, Mark Wielaard wrote:
> Hi Martin,
> 
> On Mon, 2021-04-19 at 15:18 +0200, Martin Liška wrote:
>> I made similar changes to binutils some time ago and I would like to
>> come up with the same function for elfutils. Note that current
>> construct
>> is quite error prone, I found for instance these 2 bad usages:
>>
>> diff --git a/libdwfl/relocate.c b/libdwfl/relocate.c
>> index 88b5211d..b6de3510 100644
>> --- a/libdwfl/relocate.c
>> +++ b/libdwfl/relocate.c
>> @@ -518,7 +518,7 @@ relocate_section (Dwfl_Module *mod, Elf
>> *relocated, const GElf_Ehdr *ehdr,
>>         Nothing to do here.  */
>>      return DWFL_E_NOERROR;
>>  
>> -  if (strncmp (tname, ".zdebug", strlen ("zdebug")) == 0)
>> +  if (strncmp (tname, ".zdebug", strlen (".zdebug")) == 0)
>>      elf_compress_gnu (tscn, 0, 0);
>>  
>>    if ((tshdr->sh_flags & SHF_COMPRESSED) != 0)
>> @@ -539,7 +539,7 @@ relocate_section (Dwfl_Module *mod, Elf
>> *relocated, const GElf_Ehdr *ehdr,
>>    if (sname == NULL)
>>      return DWFL_E_LIBELF;
>>  
>> -  if (strncmp (sname, ".zdebug", strlen ("zdebug")) == 0)
>> +  if (strncmp (sname, ".zdebug", strlen (".zdebug")) == 0)
>>      elf_compress_gnu (scn, 0, 0);
>>  
>>    if ((shdr->sh_flags & SHF_COMPRESSED) != 0)
> 
> Urgh. Thanks for finding this!
> 
>> I'm not convinced about function declaration in system.h. Is it a
>> proper location?
> 
> Yes, I think it is.
> 
>> And the function is not used in debuginfod/debuginfod-client.c and
>> debuginfod/debuginfod.cxx.
>> I would need another decl for these, am I right?
> 
> I think they both can simply include system.h (might want to double
> check the -I search path in debuginfod/Makefile.am) because system.h
> should be stand-alone, you don't need to link to anything else.

All right, there was a different problem I had:

In file included from ../lib/system.h:39,

                 from debuginfod.cxx:40:

../lib/system.h: In function ‘ssize_t write_retry(int, const void*, size_t)’:

../lib/system.h:135:56: error: pointer of type ‘void *’ used in arithmetic [-Werror=pointer-arith]

  135 |       ssize_t ret = TEMP_FAILURE_RETRY (write (fd, buf + recvd, len - recvd));

      |                                                    ~~~~^~~~~~~


I fixed that in the attached patch.

> 
> Maybe for debuginfod.cxx there is a better C++ way for strings. But if
> it uses C strings, then it could also simply include system.h.

Apparently, it's not using strncmp with a string objects.

Is the patch ready to be installed?
Thanks,
Martin

> 
> Thanks,
> 
> Mark
> 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-Come-up-with-startswith-function.patch
Type: text/x-patch
Size: 26474 bytes
Desc: not available
URL: <https://sourceware.org/pipermail/elfutils-devel/attachments/20210421/9d694c72/attachment-0001.bin>