optimization/5979: -fomit-frame-pointer inoperative in GCC 3.0.4 (x86)

optimization/5979: -fomit-frame-pointer inoperative in GCC 3.0.4 (x86)

[mrj]

>Number:         5979
>Category:       optimization
>Synopsis:       -fomit-frame-pointer inoperative in GCC 3.0.4 (x86)
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          pessimizes-code
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 16 03:26:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Mark Reginald James
>Release:        3.0.4
>Organization:
>Environment:
System: Linux 2.4.18 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../src/configure --prefix=/usr --with-cpu=athlon
>Description:
In 3.0.4 the ebp register is used as a frame pointer despite use of the -fomit-frame-pointer option.
>How-To-Repeat:
Compile this program:

main()
{
	int a=1;
}

with options -S -fomit-frame-pointer, and note used of epb
in the assembly output.
>Fix:
Change any assembly-coded function that expects epb to be unused to save and restore the epb register.
>Release-Note:
>Audit-Trail:
>Unformatted:

Re: optimization/5979: -fomit-frame-pointer inoperative in GCC 3.0.4 (x86)

[rth]

Synopsis: -fomit-frame-pointer inoperative in GCC 3.0.4 (x86)

State-Changed-From-To: open->closed
State-Changed-By: rth
State-Changed-When: Wed Apr  3 02:30:41 2002
State-Changed-Why:
    GCC is aligning the stack for any functions that main might
    call, since we can't trust the system startup code to do it
    properly.
    
    Examine any other function besides main and you'll see that
    the frame pointer does indeed get eliminated.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5979