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

[Glenn Washburn]

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.

Glenn

[1]
https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/valops.c;hb=HEAD#l169

> 
> Daniel