Re: [PATCH] MIPS: o32 application running on 64bit kernel core dump

[David Daney <ddaney@caviumnetworks.com>]

Yong Zhang wrote:
> If an o32 application crashes and generates a core dump on
> a 64 bit kernel, the core file will not be correctly
> recognized. This is because ELF_CORE_COPY_REGS and
> ELF_CORE_COPY_TASK_REGS are not correctly defined for o32
> and will use the default register set which would
> be CONFIG_64BIT in asm/elf.h.
> 
> So we'll switch to use the right register defines in
> this situation by checking for WANT_COMPAT_REG_H and
> use the right defines of ELF_CORE_COPY_REGS and
> ELF_CORE_COPY_TASK_REGS.

This patch looks plausible.  How was it tested?

Can you still obtain good core files with at 32-bit kernel?

Are usable core files obtained for all three ABIs on 64-bit kernels?

Other than that, I have only the one comment below.

Thanks,
David Daney


> 
> Signed-off-by: Yong Zhang <yong.zhang@windriver.com>
> ---
>  arch/mips/include/asm/elf.h      |    4 ++++
>  arch/mips/include/asm/reg.h      |    2 +-
>  arch/mips/kernel/binfmt_elfo32.c |   20 +++++++++++++++++---
>  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
> index d58f128..7990694 100644
> --- a/arch/mips/include/asm/elf.h
> +++ b/arch/mips/include/asm/elf.h
> @@ -316,9 +316,13 @@ extern void elf_dump_regs(elf_greg_t *, struct pt_regs *regs);
>  extern int dump_task_regs(struct task_struct *, elf_gregset_t *);
>  extern int dump_task_fpu(struct task_struct *, elf_fpregset_t *);
>  
> +#ifndef ELF_CORE_COPY_REGS
>  #define ELF_CORE_COPY_REGS(elf_regs, regs)			\
>  	elf_dump_regs((elf_greg_t *)&(elf_regs), regs);
> +#endif
> +#ifndef ELF_CORE_COPY_TASK_REGS
>  #define ELF_CORE_COPY_TASK_REGS(tsk, elf_regs) dump_task_regs(tsk, elf_regs)
> +#endif
>  #define ELF_CORE_COPY_FPREGS(tsk, elf_fpregs)			\
>  	dump_task_fpu(tsk, elf_fpregs)
>  
> diff --git a/arch/mips/include/asm/reg.h b/arch/mips/include/asm/reg.h
> index 634b55d..910e71a 100644
> --- a/arch/mips/include/asm/reg.h
> +++ b/arch/mips/include/asm/reg.h
> @@ -69,7 +69,7 @@
>  
>  #endif
>  
> -#ifdef CONFIG_64BIT
> +#if defined(CONFIG_64BIT) && !defined(WANT_COMPAT_REG_H)
>  
>  #define EF_R0			 0
>  #define EF_R1			 1
> diff --git a/arch/mips/kernel/binfmt_elfo32.c b/arch/mips/kernel/binfmt_elfo32.c
> index e1333d7..53bc6b4 100644
> --- a/arch/mips/kernel/binfmt_elfo32.c
> +++ b/arch/mips/kernel/binfmt_elfo32.c
> @@ -53,6 +53,23 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
>  #define ELF_ET_DYN_BASE         (TASK32_SIZE / 3 * 2)
>  
>  #include <asm/processor.h>
> +
> +/*
> + * When this file is selected, we are definitely running a 64bit kernel.
> + * So using the right regs define in asm/reg.h
> + */
> +#define WANT_COMPAT_REG_H
> +
> +/* These MUST be defined before elf.h gets included */
> +extern void elf32_core_copy_regs(elf_gregset_t grp, struct pt_regs *regs);
> +#define ELF_CORE_COPY_REGS(_dest, _regs) elf32_core_copy_regs(_dest, _regs);
> +#define ELF_CORE_COPY_TASK_REGS(_tsk, _dest)				\
> +({									\
> +	int __res = 1;							\
> +	elf32_core_copy_regs((*_dest), (task_pt_regs(_tsk)));		\
> +	__res;								\

Why does __res exist?  Can't you have that last line just be '1;'?

> +})
> +
>  #include <linux/module.h>
>  #include <linux/elfcore.h>
>  #include <linux/compat.h>
> @@ -110,9 +127,6 @@ jiffies_to_compat_timeval(unsigned long jiffies, struct compat_timeval *value)
>  	value->tv_usec = rem / NSEC_PER_USEC;
>  }
>  
> -#undef ELF_CORE_COPY_REGS
> -#define ELF_CORE_COPY_REGS(_dest, _regs) elf32_core_copy_regs(_dest, _regs);
> -
>  void elf32_core_copy_regs(elf_gregset_t grp, struct pt_regs *regs)
>  {
>  	int i;