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From: Elena Zannoni <ezannoni@redhat.com>
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Date: Mon, 16 Feb 2004 15:47:00 -0000
To: fnf@redhat.com
Cc: gdb-patches@sources.redhat.com
Subject: Re: [RFA] Handle sh-elf-gcc scheduling code into a prologue when no debug info present
In-Reply-To: <200402121505.37560.fnf@ninemoons.com>
References: <200402121505.37560.fnf@ninemoons.com>
X-SW-Source: 2004-02/txt/msg00404.txt.bz2

Fred Fish writes:
 > For the following test case:
 > 
 >   sub1 ()
 >   {
 >     printf ("In sub1\n");
 >   }
 >   
 >   sub2 ()
 >   {
 >     printf ("In sub2\n");
 >   }
 >   
 >   main ()
 >   {
 >     sub1 ();
 >     sub2 ();
 >   }
 > 


Is this in our testsuite? (it looks familiar) If not could it be added? 

 > sh-elf-gcc with -O2 will schedule the code to call sub1 into the
 > prologue of main.  If the code is compiled WITHOUT debug info, the
 > prologue scanner in gdb will not stop when it sees the jsr and will
 > eventually return a pc somewhere after the jsr.  For example:
 > 
 >   (gdb) br main
 >   Breakpoint 1 at 0x1162
 >   (gdb) x/8i main
 >   0x1158 <main>:	mov.l	r14,@-r15
 >   0x115a <main+2>:	mov.l	0x116c <main+20>,r0	! 0x1120
 >   0x115c <main+4>:	sts.l	pr,@-r15
 >   0x115e <main+6>:	jsr	@r0
 >   0x1160 <main+8>:	mov	r15,r14
 > * 0x1162 <main+10>:	mov.l	0x1170 <main+24>,r1	! 0x113c
 >   0x1164 <main+12>:	mov	r14,r15
 >   0x1166 <main+14>:	lds.l	@r15+,pr
 > 
 > Note that the breakpoint on main() gets set well after the jsr.  When
 > you set breakpoints at sub1 and sub2 and run the program, you get:
 > 
 >   (gdb) run
 >   Starting program: /links1/build/sourceware/gdb/T-sh-elf/gdb/g 
 >   Breakpoint 2, 0x00001128 in sub1 ()
 >   (gdb) c
 >   Continuing.
 >   In sub1
 >   Breakpoint 1, 0x00001162 in main ()
 >   (gdb) c
 >   Continuing.
 >   Breakpoint 3, 0x00001144 in sub2 ()
 >   (gdb) c
 >   Continuing.
 >   In sub2
 >   Program exited with code 012.
 > 
 > which is very confusing because it appears that sub1 is called before main!
 > 
 > With the attached patch, the prologue scanner returns the pc of the
 > jsr instruction, allowing the breakpoint at main to be hit before the
 > breakpoint at sub1:
 > 

OK.