c - How the linker calculate the size of .bss section? -


The

I want to know how Linkkrta .bss calculating section size?

I have a test program with two variables, one has to start at zero, the start of the second zero I hope .bss size 4 and it is. 

  # cat test.c & amp; Amp; GCC-O Test O-C Test C & amp; LD-O Test Test O & amp; amp; Readelf -Ss test int _start = 0; Int a = 2; ...... Section Headings: [NR] Name Type Address Offset Size EntSize Flags Link Information Align [1]. Data PROGBITS 00000000006000b0 000000b0 0000000000000004 0000000000000000 WA 0 4 4 [2] .bss NOBITS 00000000006000b4 000000b4 0000000000000004 000000000000000004 000000000000000004 000000000000000000 WA 0 4 4 points :: value size of binding vis NDX name 6: 00000000006000b4 4 object global default 2 10 _start: ..... symbols include table '.symtab' 11 entries 00000000006000b0 4 object global default 1  < / Pre> 
 Then I add another zero-initial value. This time I hope the size of .bss is 8, but this is 12 (0xc).  
  # cat test.c & amp; Amp; GCC-O Test O-C Test C & amp; LD-O Test Test O & amp; amp; Readelf -Ss test int _start = 0; Int a = 2; Int b = 0; ...... Section Headings: [NR] Name Type Address Offset Size EntSize Flags Link Information Align [1]. Data PROGBITS 00000000006000b0 000000b0 0000000000000004 000000000000000000 WA 0 4 4 [2] .bss Nobbit 00000000006000b4 000000b4 000000000000000c 00000000000000000c 00000000000000000c 0000000000000000 WA 0 4 4 points :: value tied to the size of vis NDX name 6: 00000000006000b8 4 object global default 2B 7: 00000000006000b4 4 object global default 2 _start 11: 00000000006000b0 4 object global default ...... symbol table '.symtab' 12 entries included 1 one   
 I initialazed the third zero- Continue adding and this time I hope .bss size 12 and it is.  
  # cat test.c & amp; Amp; GCC-O Test O-C Test C & amp; LD-O Test Test O & amp; amp; Readelf -Ss test int _start = 0; Int a = 2; Int b = 0; Int c = 0; ...... section headers: [Nr] Name Type Address Offset Size EntSize align flag link information [0] zero 0000000000000000 00000000 0000000000000000 0000000000000000 0 0 0 [1] .data PROGBITS 00000000006000b0 000000b0 0000000000000004 -0000000000000000 Washington 0 0 4 [2 ] .bss NOBITS 00000000006000b4 000000b4 000000000000000 C 00000000000000000 C 000000000000000000 WA 0 4 4 ...... symbol table 13 entries '.symtab': number value size type bind vis Andiaks name 6: 00000000006000b8 4 object global default 2 B7: 00000000006000b4 4 Object global default 2 _start 8: 00000000006000 BC4Ab Global crop would keep the default 2 C 12: 00000000006000b0 4 object global default 1   
 I continue to add the fourth zero-initial value. This time I hope the size of .bss is 16, but this is 20 (0x14).  
  # cat test.c & amp; Amp; GCC-O Test O-C Test C & amp; LD-O Test Test O & amp; amp; Readelf -Ss test int _start = 0; Int a = 2; Int b = 0; Int c = 0; Int d = 0; ...... Section Headings: [NR] Name Type Address Offset Size EntSize Flags Link Information Align [1]. Data PROGBITS 00000000006000b0 000000b0 0000000000000004 0000000000000000 WA 0 4 4 [2] .bss NOBITS 00000000006000b4 000000b4 0000000000000014 000000000000000014 000000000000000014 0000000000000000 WA 0 4 4 points :: Value size Type bound by NDX name 6: 00000000006000b8 4 Object global default 2 b 7: 00000000006000b4 4 Object global default 2 _start 8: 00000000006000bc 4 Item global default ...... Symbol table '.symtab' 14 entries included 2C10: 00000000006000C4 Object Global DIFA T 2 D 13: 00000000006000b0 4 object global default 1 matches a   
 Sometimes the results I expected, not sometimes. Does any other factor affect the output of the linker?   
 
 
 This is really alignment. The size of  bss  in your example is not the expected by 8-byte combinations, but that's because you have 4 bytes of  data  if you add a second initial variable, So you will see that the size of the  bss  segment is 8 bytes aligned.

Comments

Post a Comment

Popular posts from this blog

Python SQLAlchemy：AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema' -

I tried to create a new database in my project, but when I run the script, I get this error, I have another project, this type of definition worked before, but now it gets a single error. I am using Python 2.7.8 and the version of SQLAlchemy module is 0.9.8. By the way, using a project flask- SQLAlchemy, it works well, I'm confused. Traceback information is as follows: Traceback (most recent call final): File "D: / Projects / IOM / db_create.py", line 4, & lt; Module & gt; From the models the base file "D: \ Projects \ OO-IM \ models.py", in line 15, in the & lt; Module & gt; Column ( 'followed_id', int (), ForeignKey ( 'user.id')) file "C: \ Python27 \ lib \ site-packages \ SQLAlchemy \ SQL \ schema.py", line 369, __new__ schema = metadata. Schema file "C: \ Python27 \ lib \ site-packages \ SQLAlchemy \ SQL \ elements.py", line 662, AttributeError in __getattr__ key): Neither 'column' object nor ...
Read more

java - How not to audit a join table and related entities using Hibernate Envers? -

I use Eners to be hibernate to audit my institutions. I have an audit entity, Foo , which includes a list & lt; Bars & gt; However, I do not want to audit the bar institutions, in the form of properties, I have written that: @inti @edicated public class Foo {@JoinTable (name = "T_FOO_BAR", joinColumns = @JoinColumn (name = "FOO_ID"), inverseJoinColumns = @JoinColumn (Name = "BAR_ID")) @ManyToMany (Cascade = Persist) @ Indited (targetAuditMode = RelationTargetAuditMode.NOT_AUDITED ) Public listing & lt; Bars & gt; GetBars () {Return bars; }} Now, I want to retrieve an amendment of foo : AuditReader reader = AuditReaderFactory.get (GetEntityManager ()); FU modification = (FU) reader.CreativeTeA () .entensEtrevision (Foo Class, 42) .getSingleResult (); Unfortunately, when I want to retrieve all the data (i.e. when it loads lazy times ), error me ORA-00942: table or view is not present , because Tried to query this: Sel...
Read more

mongodb - CakePHP paginator ignoring order, but only for certain values -

While pagging my user model in kppp, I can sort with some values, but not others. For example, I can order results from created or email , for example, but username or reputation seems to come back order by arbitrary command for example with a list of users: $ this-> paginate = array ('condition' => array ( 'User.is_active' = & gt; true), 'border' => 24, 'order' => array ('User.created' => DESC)); Works as expected, but $ this - & gt; Paged = array ('conditions' = & gt; array (' user.isIactive '= & gt; true),' border '= & gt; 24,' command '= & gt; array (' user repeats' = ' & Gt; DESC ')); No, no. I first thought that this could be a database issue, but when I search the database directly, sorted as expected. Note: I am using Mangodebi with the Mongo DB plugin of Ichikawa for the KPPHP; Pagnetizing users are used to work properl...
Read more