Re: [PATCH] gdb: Add malloc and free symbols to kernel.exec to improve gdb functionality

[Daniel Kiper]

On Wed, Mar 09, 2022 at 02:25:28PM -0600, Glenn Washburn wrote:
> On Wed, 9 Mar 2022 16:49:57 +0100
> Daniel Kiper <dkiper@net-space.pl> wrote:
>
> > On Wed, Mar 02, 2022 at 06:25:12PM -0600, Glenn Washburn wrote:
> > > Add linker flags when linking kernel.exec to have malloc and free point to
> > > grub_malloc and grub_free respectively. Some gdb functionality depends on
> > > gdb locating the symbols "malloc" and "free", such as dynamically creating
> > > strings for arguments to injected function calls. A trivial example would
> > > the gdb command 'p strlen("astring")'.
> > >
> > > Signed-off-by: Glenn Washburn <development@efficientek.com>
> > > ---
> > > This should have been included in the gdb patch series I recently sent,
> > > although its not required by nor requires any of those patches.
> > >
> > > Glenn
> > >
> > > ---
> > >  conf/Makefile.common | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/conf/Makefile.common b/conf/Makefile.common
> > > index f0bb6e160a..069b428c1a 100644
> > > --- a/conf/Makefile.common
> > > +++ b/conf/Makefile.common
> > > @@ -36,6 +36,7 @@ BUILD_CPPFLAGS += $(CPPFLAGS_DEFAULT)
> > >
> > >  CFLAGS_KERNEL = $(CFLAGS_PLATFORM) -ffreestanding
> > >  LDFLAGS_KERNEL = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC)
> > > +LDFLAGS_KERNEL += -Wl,--defsym=malloc=grub_malloc 
> > > -Wl,--defsym=free=grub_free
> >
> > Could not we teach gdb somehow to use grub_malloc()/grub_free() instead
> > of malloc()/free()?
>
> Considering the tons of options that GDB has, I was hoping the same
> thing. Unfortunately, it appears to be hardcoded[1]. So not without
> changing the source.

:-( I expected you checked that but wanted to be sure... :-)

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel