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

To: Yong Zhang <yong.zhang@windriver.com>
Subject: Re: [PATCH] MIPS: o32 application running on 64bit kernel core dump
From: David Daney <ddaney@caviumnetworks.com>
Date: Wed, 01 Jul 2009 12:09:10 -0700
Cc: linux-kernel@vger.kernel.org, ralf@linux-mips.org, linux-mips <linux-mips@linux-mips.org>
In-reply-to: <16bd35f2910f585740f4764fa1e80bf31c80d576.1242178813.git.yong.zhang@windriver.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <16bd35f2910f585740f4764fa1e80bf31c80d576.1242178813.git.yong.zhang@windriver.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Thunderbird 2.0.0.21 (X11/20090320)
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;


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