Size of an hex in x64 Assembly











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I'm trying to try all the variants of the x command in assembly. I typed



(gdb) x /x $rsp

0x7fffffffdf90: 0x01


According to my book the x/x command select the first 8 bytes from rsp and write them as an hex. However, looking for the assembly documentation (gdb help) i have not found anywhere that the size of /x is explicitly 8 byte. So how do I know if it is really 8 bytes ?






assembly gdb







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  • Use a count larger than 1 to see what the grouping is, and what the gap is to the next address. Or dump something that definitely doesn't have zeros in the high bytes, because 0x01 and 0x00000001 might both print the same, but 0xDEADBEEF is unambiguously (at least) 4 bytes.
    – Peter Cordes
    Nov 13 at 7:19

















up vote
0
down vote

favorite












I'm trying to try all the variants of the x command in assembly. I typed



(gdb) x /x $rsp

0x7fffffffdf90: 0x01


According to my book the x/x command select the first 8 bytes from rsp and write them as an hex. However, looking for the assembly documentation (gdb help) i have not found anywhere that the size of /x is explicitly 8 byte. So how do I know if it is really 8 bytes ?






assembly gdb







share|improve this question






















  • Use a count larger than 1 to see what the grouping is, and what the gap is to the next address. Or dump something that definitely doesn't have zeros in the high bytes, because 0x01 and 0x00000001 might both print the same, but 0xDEADBEEF is unambiguously (at least) 4 bytes.
    – Peter Cordes
    Nov 13 at 7:19















up vote
0
down vote

favorite









up vote
0
down vote

favorite











I'm trying to try all the variants of the x command in assembly. I typed



(gdb) x /x $rsp

0x7fffffffdf90: 0x01


According to my book the x/x command select the first 8 bytes from rsp and write them as an hex. However, looking for the assembly documentation (gdb help) i have not found anywhere that the size of /x is explicitly 8 byte. So how do I know if it is really 8 bytes ?






assembly gdb







share|improve this question













I'm trying to try all the variants of the x command in assembly. I typed



(gdb) x /x $rsp

0x7fffffffdf90: 0x01


According to my book the x/x command select the first 8 bytes from rsp and write them as an hex. However, looking for the assembly documentation (gdb help) i have not found anywhere that the size of /x is explicitly 8 byte. So how do I know if it is really 8 bytes ?






assembly gdb




assembly gdb






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asked Nov 13 at 7:10









Koinos

367




367












  • Use a count larger than 1 to see what the grouping is, and what the gap is to the next address. Or dump something that definitely doesn't have zeros in the high bytes, because 0x01 and 0x00000001 might both print the same, but 0xDEADBEEF is unambiguously (at least) 4 bytes.
    – Peter Cordes
    Nov 13 at 7:19




















  • Use a count larger than 1 to see what the grouping is, and what the gap is to the next address. Or dump something that definitely doesn't have zeros in the high bytes, because 0x01 and 0x00000001 might both print the same, but 0xDEADBEEF is unambiguously (at least) 4 bytes.
    – Peter Cordes
    Nov 13 at 7:19


















Use a count larger than 1 to see what the grouping is, and what the gap is to the next address. Or dump something that definitely doesn't have zeros in the high bytes, because 0x01 and 0x00000001 might both print the same, but 0xDEADBEEF is unambiguously (at least) 4 bytes.
– Peter Cordes
Nov 13 at 7:19






Use a count larger than 1 to see what the grouping is, and what the gap is to the next address. Or dump something that definitely doesn't have zeros in the high bytes, because 0x01 and 0x00000001 might both print the same, but 0xDEADBEEF is unambiguously (at least) 4 bytes.
– Peter Cordes
Nov 13 at 7:19














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So how do I know if it is really 8 bytes ?




It's not. It's "whatever size you used last". Documentation.



For example:



(gdb) x/bx $rsp

0x7fffffffcbc8: 0x1c


Subsequent x/x commands will use size 1 (a single char):



(gdb) x/x $rsp

0x7fffffffcbc8: 0x1c


You can override the size explicitly:



(gdb) x/gx $rsp

0x7fffffffcbc8: 0x00007ffff7ddc61c


Subsequent x/x commands now default to size 8:



(gdb) x/x $rsp

0x7fffffffcbc8: 0x00007ffff7ddc61c





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    So how do I know if it is really 8 bytes ?




    It's not. It's "whatever size you used last". Documentation.



    For example:



    (gdb) x/bx $rsp
    
0x7fffffffcbc8: 0x1c


    Subsequent x/x commands will use size 1 (a single char):



    (gdb) x/x $rsp
    
0x7fffffffcbc8: 0x1c


    You can override the size explicitly:



    (gdb) x/gx $rsp
    
0x7fffffffcbc8: 0x00007ffff7ddc61c


    Subsequent x/x commands now default to size 8:



    (gdb) x/x $rsp
    
0x7fffffffcbc8: 0x00007ffff7ddc61c





    share|improve this answer

























      up vote
      1
      down vote














      So how do I know if it is really 8 bytes ?




      It's not. It's "whatever size you used last". Documentation.



      For example:



      (gdb) x/bx $rsp
      
0x7fffffffcbc8: 0x1c


      Subsequent x/x commands will use size 1 (a single char):



      (gdb) x/x $rsp
      
0x7fffffffcbc8: 0x1c


      You can override the size explicitly:



      (gdb) x/gx $rsp
      
0x7fffffffcbc8: 0x00007ffff7ddc61c


      Subsequent x/x commands now default to size 8:



      (gdb) x/x $rsp
      
0x7fffffffcbc8: 0x00007ffff7ddc61c





      share|improve this answer























        up vote
        1
        down vote










        up vote
        1
        down vote










        So how do I know if it is really 8 bytes ?




        It's not. It's "whatever size you used last". Documentation.



        For example:



        (gdb) x/bx $rsp
        
0x7fffffffcbc8: 0x1c


        Subsequent x/x commands will use size 1 (a single char):



        (gdb) x/x $rsp
        
0x7fffffffcbc8: 0x1c


        You can override the size explicitly:



        (gdb) x/gx $rsp
        
0x7fffffffcbc8: 0x00007ffff7ddc61c


        Subsequent x/x commands now default to size 8:



        (gdb) x/x $rsp
        
0x7fffffffcbc8: 0x00007ffff7ddc61c





        share|improve this answer













        So how do I know if it is really 8 bytes ?




        It's not. It's "whatever size you used last". Documentation.



        For example:



        (gdb) x/bx $rsp
        
0x7fffffffcbc8: 0x1c


        Subsequent x/x commands will use size 1 (a single char):



        (gdb) x/x $rsp
        
0x7fffffffcbc8: 0x1c


        You can override the size explicitly:



        (gdb) x/gx $rsp
        
0x7fffffffcbc8: 0x00007ffff7ddc61c


        Subsequent x/x commands now default to size 8:



        (gdb) x/x $rsp
        
0x7fffffffcbc8: 0x00007ffff7ddc61c






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 13 at 16:05









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