Rightio :) I guess that's what 2 hours of sleep gets you ;)
On 4/15/05, Niko Matsakis <niko@xxxxxxxxxxxx> wrote:
> I think he is asking if you could point out the file in the gcc source
> code which contains the code which causes the "sub" instruction which
> establishes the stack frame to be inserted.
>
> To wyj-me: I don't know the answer, but I doubt there will be one file.
> Probably there is some file which computes the size that the stack
> frame for the function ought to be, taking into account all variables
> and determines where on that stack frame they lie, and a separate file
> that emits the prologue for the function. Or at least separate
> subroutines.
>
>
> Niko
>
> On Apr 15, 2005, at 12:52 PM, Brian Budge wrote:
>
> > Hi there -
> >
> > I could be wrong, but in this case the variable "buf" is being placed
> > on the stack. The sub instruction is being used to move the stack
> > pointer. No library call is being made.
> >
> > Brian
> >
> > On 4/15/05, wyj-me <wyj3390@xxxxxxxxxxxxxxxxxx> wrote:
> >> Dear friend,
> >> First of all, thank you for reading my letter.
> >> I am a student.When I do researches about the buffer
> >> overflow, I meet a question and want to get your help.Please permit
> >> me to illustrate it with the following example:
> >> First, provided we have such a simple program named as
> >> test001.c.
> >> -------------------------------
> >> int main()
> >> {
> >> char buf[10];
> >> int i;
> >>
> >> i=0;
> >> return 1;
> >> }
> >> -------------------------------
> >> If we compile the program with the command: gcc -S test001.s
> >> test001.c, show the content of the test001.s, we can get the
> >> following:
> >> -------------------------------
> >> .file 'test001.c'
> >> .text
> >> .globl main
> >> .type main,@function
> >> main:
> >> pushl %ebp
> >> movl %esp,%ebp
> >> subl $40,%esp
> >> andl $-16,%esp
> >> movl $0,%eax
> >> subl %eax,%esp
> >> movl $0,-28(%ebp)
> >> movl $1,%eax
> >> leave
> >> ret
> >> .Lfel:
> >> .size main,.Lfel-main
> >> .ident 'GCC(GNU)3.2.2 20030222(Red Hat Linux(3.2.2-5)'
> >> --------------------------------
> >> From the above, we can know that the instruction 'subl
> >> $40,%esp' is used to allocate the space for the buf[] and i. My
> >> trouble is that I don't know in which function the 'subl $40,%esp' is
> >> introduced. Now I want to add some instructions before
> >> the 'subl $40,%esp' to set some flags to indicate the end of the
> >> string. I hope you can tell me which sourcecode file I should look
> >> through among so many sourcecode files with the gcc tool.
> >> Thanks again.
> >> Look forward to your answer.
> >> Sincerely,
> >>
> >>
> >> Yejun Wang
> >>
> >>
> >> wyj-me
> >> wyj3390@xxxxxxxxxxxxxxxxx
> >> 2005-04-15
> >>
>
>
