[patch/idea] Add register scrambling to testsuite

[H.J. Lu]

On Fri, Jun 10, 2022 at 8:53 PM DJ Delorie via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
> [Note: I tried to add a special case for the bug noted below, but ran
> out of time while trying to learn enough ppc64/vsx opcodery]
>
> Allow for target-specific register "scrambling" - loading arbitrary
> values into all registers that need not be call-saved.  These values
> should be non-zero and invalid addresses, to help catch inadvertent
> uses of otherwise uninitialized registers.
>
> Intended to help prevent bugs such as those fixed by
> 0218463dd8265ed937622f88ac68c7d984fe0cfc
>
> diff --git a/support/Makefile b/support/Makefile
> index 9b50eac117..91b940c379 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -76,6 +76,7 @@ libsupport-routines = \
>    support_quote_string \
>    support_record_failure \
>    support_run_diff \
> +  support_scramble_registers \
>    support_select_modifies_timeout \
>    support_select_normalizes_timeout \
>    support_set_small_thread_stack_size \
> diff --git a/support/support.h b/support/support.h
> index d20051da4d..3d049575d0 100644
> --- a/support/support.h
> +++ b/support/support.h
> @@ -233,6 +233,11 @@ void support_stack_free (struct support_stack *stack);
>     The returned value is the lowest file descriptor number.  */
>  int support_open_dev_null_range (int num, int flags, mode_t mode);
>
> +/* Write arbitrary values to all registers that can be written do, to
> +   avoid assumptions about initial register contents in test
> +   cases.  */
> +void support_scramble_registers (void);
> +
>  __END_DECLS
>
>  #endif /* SUPPORT_H */
> diff --git a/support/support_scramble_registers.c b/support/support_scramble_registers.c
> new file mode 100644
> index 0000000000..d5e2d3fd6d
> --- /dev/null
> +++ b/support/support_scramble_registers.c
> @@ -0,0 +1,29 @@
> +/* scramble any call-not-preserved registers
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <support/support.h>
> +
> +#include "scramble-regs.h"
> +
> +void
> +support_scramble_registers(void)
> +{
> +#ifdef SCRAMBLE_REGS
> +  SCRAMBLE_REGS;
> +#endif
> +}
> diff --git a/support/support_test_main.c b/support/support_test_main.c
> index 60307fd68e..0ccb182791 100644
> --- a/support/support_test_main.c
> +++ b/support/support_test_main.c
> @@ -269,6 +269,8 @@ adjust_exit_status (int status)
>  int
>  support_test_main (int argc, char **argv, const struct test_config *config)
>  {
> +  support_scramble_registers();
> +
>    if (test_main_called)
>      {
>        printf ("error: test_main called for a second time\n");
> diff --git a/sysdeps/generic/scramble-regs.h b/sysdeps/generic/scramble-regs.h
> new file mode 100644
> index 0000000000..7ac55d1bfc
> --- /dev/null
> +++ b/sysdeps/generic/scramble-regs.h
> @@ -0,0 +1,36 @@
> +/* scramble any call-not-preserved registers, target portion.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Example target-specific usage:
> +
> +   #define SCRAMBLE_REGS \
> +     asm volatile ("movl %0, %%eax" :: "i" (1234)); \
> +     asm volatile ("movl %0, %%edx" :: "i" (5678));
> +
> +   Targets are encouraged to create their own target-specific sub-definitions, like
> +
> +   #ifndef SCRAMBLE_REGS_FPU
> +   #define SCRAMBLE_REGS_FPU
> +   #endif
> +   #define SCRAMBLE_REGS \
> +     SCRAMBLE_REGS_FPU \
> +     asm volatile ("..."); \
> +
> +*/
> +
> +/* #define SCRAMBLE_REGS */
> diff --git a/sysdeps/powerpc/scramble-regs.h b/sysdeps/powerpc/scramble-regs.h
> new file mode 100644
> index 0000000000..9400b2ed6b
> --- /dev/null
> +++ b/sysdeps/powerpc/scramble-regs.h
> @@ -0,0 +1,20 @@
> +/* scramble any call-not-preserved registers, powerpc version
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#define SCRAMBLE_REGS                 \
> +  asm volatile ("li 0, %0" :: "i" (0x1235));
> diff --git a/sysdeps/x86_64/scramble-regs.h b/sysdeps/x86_64/scramble-regs.h
> new file mode 100644
> index 0000000000..66ffab3c8b
> --- /dev/null
> +++ b/sysdeps/x86_64/scramble-regs.h
> @@ -0,0 +1,31 @@
> +/* scramble any call-not-preserved registers, x86_64 version
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* SysV ABI: preserve EBX, ESP, EBP and R12-R15.  */
> +
> +#define SCRAMBLE_REGS                 \
> +  asm volatile ("movl %0, %%eax" :: "i" (0x12345679)); \
> +  asm volatile ("movl %0, %%ecx" :: "i" (0x12345679)); \
> +  asm volatile ("movl %0, %%edx" :: "i" (0x12345679)); \
> +  asm volatile ("movl %0, %%esi" :: "i" (0x12345679)); \
> +  asm volatile ("movl %0, %%edi" :: "i" (0x12345679)); \
> +  asm volatile ("mov %0, %%r8"  :: "i" (0x12345679));  \
> +  asm volatile ("mov %0, %%r9"  :: "i" (0x12345679));  \
> +  asm volatile ("mov %0, %%r10" :: "i" (0x12345679));  \
> +  asm volatile ("mov %0, %%r11" :: "i" (0x12345679));  \
> +
>

Should we also scramble XMM/YMM/ZMM registers?

-- 
H.J.