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Re: advice on reducing C stack frame size?

From: Ken Raeburn
Subject: Re: advice on reducing C stack frame size?
Date: Tue, 16 Sep 2008 01:27:45 -0400

On Sep 13, 2008, at 12:56, Andy Wingo wrote:
So for example, just sitting at the repl, we have:

#27 0x0014e99b in scm_apply (proc=0xb7f0d718, arg1=0x404, args=0x404) at eval.i.c:1656
   1656     return scm_dapply (proc, arg1, args);
#28 0x001c48fc in vm_run (vm=0xb7f1ff58, program=0x8d53df8, args=0x404) at vm-i-system.c:510
   510        *sp = scm_apply (x, args, SCM_EOL);
   (gdb) p sp - vp->stack_base
   $3 = 104
   (gdb) up
#29 0x001bfcad in program_apply (program=0xb7ee2730, args=0x404) at programs.c:126
   126    return scm_vm_apply (scm_the_vm (), program, args);
   (gdb) p 0x001c48fc - 0x001bfcad
   $4 = 19535

The difference between #29 and #28 is the size of the vm_run() stack
frame (I think).

Aren't those the program counter addresses you're looking at? Note that the value at #29 is in between #27 and #28. Stack frames usually don't work that way. :-)

(gdb) bt
#7  0x00079691 in captured_main ()
#8  0x00077487 in catch_errors ()
#9  0x000796d2 in gdb_main ()      <---- pc address 0x796d2
#10 0x00001f1e in main ()
(gdb) x/20i gdb_main
0x79693 <gdb_main>:       push   %ebp
0x796c6 <gdb_main+51>:    mov    %ecx,0x4(%esp)
0x796ca <gdb_main+55>:    mov    %eax,(%esp)
0x796cd <gdb_main+58>:    call   0x7743a <catch_errors>
0x796d2 <gdb_main+63>:    add    $0x14,%esp     <---- insn to return to
0x796d5 <gdb_main+66>:    mov    $0x1,%eax
0x796da <gdb_main+71>:    pop    %ebx

Try "print $sp" or "info reg" at each frame to see the stack pointer.

Or you could try disassembling the entire thing, and scan for a regexp matching near the start of a function (say, symbol name, "+", one digit or a "1" and another digit, then ">", and an instruction that adjusts the stack pointer by a 3-digit value or more. If it works, that may show you all the biggest-frame functions.


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