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

[Daniel Kiper]

On Fri, Mar 11, 2022 at 12:09:58AM +0100, Daniel Kiper wrote:
> 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>

Sadly this patch breaks Windows builds... :-(

i686-w64-mingw32-gcc -std=gnu99 -fno-common -Os -m32 -Wall -W -Wshadow 
-Wpointer-arith -Wundef -Wchar-subscripts -Wcomment -Wdeprecated-declarations 
-Wdisabled-optimization -Wdiv-by-zero -Wfloat-equal -Wformat-extra-args 
-Wformat-security -Wformat-y2k -Wimplicit -Wimplicit-function-declaration 
-Wimplicit-int -Wmain -Wmissing-braces -Wmissing-format-attribute -Wmultichar 
-Wparentheses -Wreturn-type -Wsequence-point -Wshadow -Wsign-compare -Wswitch 
-Wtrigraphs -Wunknown-pragmas -Wunused -Wunused-function -Wunused-label 
-Wunused-parameter -Wunused-value  -Wunused-variable -Wwrite-strings 
-Wnested-externs -Wstrict-prototypes -g -Wredundant-decls -Wmissing-prototypes 
-Wmissing-declarations  -Wextra -Wattributes -Wendif-labels -Winit-self 
-Wint-to-pointer-cast -Winvalid-pch -Wmissing-field-initializers -Wnonnull 
-Woverflow -Wvla -Wpointer-to-int-cast -Wstrict-aliasing -Wvariadic-macros 
-Wvolatile-register-var -Wpointer-sign -Wmissing-include-dirs 
-Wmissing-prototypes -Wmissing-declarations -Wformat=2 -march=i386 
-falign-functions=1 -falign-loops=1 -falign-jumps=1 -freg-struct-return 
-mno-mmx -mno-sse -mno-sse2 -mno-sse3 -mno-3dnow -msoft-float 
-fno-dwarf2-cfi-asm -fno-reorder-functions -mno-stack-arg-probe 
-fno-asynchronous-unwind-tables -fno-unwind-tables -fno-ident 
-mstack-protector-guard=global -fstack-protector -Wtrampolines -Werror   
-ffreestanding   -m32 -Wl,-mi386pe  -nostdlib -Wl,-N 
-Wl,--defsym=malloc=grub_malloc -Wl,--defsym=free=grub_free -Wl,-r   -o 
kernel.exec.exe kern/i386/efi/kernel_exec-startup.o 
kern/i386/efi/kernel_exec-tsc.o kern/i386/kernel_exec-tsc_pmtimer.o 
kern/i386/efi/kernel_exec-init.o bus/kernel_exec-pci.o 
kern/i386/kernel_exec-dl.o kern/i386/kernel_exec-tsc.o 
kern/i386/kernel_exec-tsc_pit.o disk/efi/kernel_exec-efidisk.o 
kern/efi/kernel_exec-efi.o kern/efi/kernel_exec-init.o 
kern/efi/kernel_exec-mm.o term/efi/kernel_exec-console.o 
kern/kernel_exec-acpi.o kern/efi/kernel_exec-acpi.o kern/efi/kernel_exec-sb.o 
kern/kernel_exec-lockdown.o kern/kernel_exec-compiler-rt.o 
kern/kernel_exec-mm.o kern/kernel_exec-time.o 
kern/generic/kernel_exec-millisleep.o kern/kernel_exec-buffer.o 
kern/kernel_exec-command.o kern/kernel_exec-corecmd.o kern/kernel_exec-device.o 
kern/kernel_exec-disk.o kern/kernel_exec-dl.o kern/kernel_exec-env.o 
kern/kernel_exec-err.o kern/kernel_exec-file.o kern/kernel_exec-fs.o 
kern/kernel_exec-list.o kern/kernel_exec-main.o kern/kernel_exec-misc.o 
kern/kernel_exec-parser.o kern/kernel_exec-partition.o 
kern/kernel_exec-rescue_parser.o kern/kernel_exec-rescue_reader.o 
kern/kernel_exec-term.o kern/kernel_exec-verifiers.o kernel_exec-symlist.o
--defsym:1: undefined symbol `grub_malloc' referenced in expression
collect2: error: ld returned 1 exit status
Makefile:29017: recipe for target 'kernel.exec.exe' failed

The GCC and ld versions do not matter much.

i686-w64-mingw32-gcc (GCC) 10-win32 20220113
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

GNU ld (GNU Binutils) 2.37
Copyright (C) 2021 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.

i686-w64-mingw32-gcc (GCC) 6.3.0 20170516
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

GNU ld (GNU Binutils) 2.28
Copyright (C) 2017 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.

Daniel