Thanks a lot for the explanation and the link!! I have just one more question about linker scripts. I am not clear about alignment of sections. Is it necessary to align sections? Can the alignment be different from 4096? In the script that I provided the text and data sections are aligned while the bss section is not. Is there a reason for it ? Thanks Vaibhav Jain On Sun, Mar 25, 2012 at 11:41 PM, Pranay Kumar Srivastava < Pranay.Shrivastava@hcl.com> wrote:
-----Original Message----- From: Vaibhav Jain [mailto:vjoss197@gmail.com] Sent: Sunday, March 25, 2012 3:19 AM To: Pranay Kumar Srivastava Subject: Re: Query on linker scripts
Hi Pranay, Thanks for replying!. I am still not clear about this as I have not reached the part of the tutorial which talks about pte and pgd. Could you please explain this point about safety of section with a simpler example?
I'll take example from your script. .bss : { sbss = .; *(COMMON) *(.bss) ebss = .; }
What I wanted to say was instead of taking ebss within .bss section you should take it outside that section. You might need to do ABSOLUTE since . will give you relative values but you'd want absolute values since addresses that you are interested in will begin from the entry point not from a section. So you can try something like this
.bss ALIGN(4096): { sbss = .; *(COMMON) *(.bss) } ebss = ABSOLUTE(.); /*This should be a page aligned address*/
Also, from your reply I figured out that it is not compulsory
to define such symbols and the names can be different than sbss and ebss. Am I right ?
The names can be anything it's your choice entirely. But being descriptive helps. You should have a close look at the redhat tutorial for linker scripts instead of following someone else's linker script since you might not require all the variables chosen or you might need some additional variables due to the design you've chosen for your kernel.
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/4/html/Using_ld_t...
Thanks Vaibhav Jain
Please include kernelnewbies@kernelnewbies.org in cc when replying. You are likely to get more responses that way.
On Sat, Mar 24, 2012 at 11:45 AM, Pranay Kumar Srivastava <Pranay.Shrivastava@hcl.com> wrote: On 03/24/2012 11:52 PM, Pranay Kumar Srivastava wrote:
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1. Query on linker scripts (Vaibhav Jain) 2. Re: Query on linker scripts (Carlo Caione)
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Message: 1 Date: Fri, 23 Mar 2012 21:43:40 -0700 From: Vaibhav Jain<vjoss197@gmail.com> Subject: Query on linker scripts To: kernelnewbies@kernelnewbies.org Message-ID:
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Hi,
Recently I have started reading tutorials for writing a small kernel. All such tutorials mention use of linker scripts. I have read few articles on linker scritps but I am stuck on one thing. I am unable to understand the use of defining new symbols in linker scripts. Using a linker script to arrange different sections in the object file is understandable but defining symbols which are not referenced anywhere in the script is confusing. An example is the use of symbols sbss and ebss in the bss section as show in the script below
ENTRY (loader) SECTIONS { . = 0x00100000; .text ALIGN (0x1000) : { *(.text) } .rodata ALIGN (0x1000) : { *(.rodata*) } .data ALIGN (0x1000) : { *(.data) } .bss : { sbss = .; *(COMMON) *(.bss) ebss = .; } }
Please explain how defining such symbols is useful.
Thanks Vaibhav Jain