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debug/10001: gcc -g puts labels before function prologue


>Number:         10001
>Category:       debug
>Synopsis:       gcc -g puts labels before function prologue
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 08 14:26:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Werner Almesberger
>Release:        3.3 20030303 (prerelease)
>Organization:
>Environment:
System: Linux ar 2.4.18 #5 Mon Mar 18 09:25:24 ART 2002 i686 unknown
Architecture: i686

	
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ./configure --prefix=/usr/local/gcc20030303/ --enable-languages=c
>Description:

gcc -g puts labels before function prologue

A variation of the breakpoint-before-prologue problem: even if we
use a label to set the breakpoint, this doesn't always help. (It
seems to avoid ill effects in functions with extern scope, though.)

>How-To-Repeat:

Example (with Red Hat's gcc 3.1 20011127 on ia32):

$ cat <<EOF >foo.c
static void foo(int blah)
{
label:
    return;
}

int main(void)
{
    foo(321);
    return 0;
}
EOF
$ gcc -g foo.c
$ readelf -w a.out
...
     DW_AT_name        : foo
...
     DW_AT_low_pc      : 0x8048398 134513560
     DW_AT_high_pc     : 0x804839d 134513565
     DW_AT_frame_base  : 1 byte block: 55       (DW_OP_reg5; )
...
     DW_AT_name        : (indirect string, offset: 0x3a): blah
...
     DW_AT_location    : 2 byte block: 91 8     (DW_OP_fbreg: 8; )
...
     DW_AT_name        : (indirect string, offset: 0x55): label
...
     DW_AT_low_pc      : 0x8048398 134513560
...
$ objdump -d a.out
...
08048398 <foo>:
 8048398:       55                      push   %ebp
 8048399:       89 e5                   mov    %esp,%ebp
 804839b:       c9                      leave
 804839c:       c3                      ret
 804839d:       90                      nop
...

>Fix:
I don't know any useful work-around, except liberally sprinkling
asm("")s all over the code.
>Release-Note:
>Audit-Trail:
>Unformatted:


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