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

[Yong Zhang]

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.

Signed-off-by: Yong Zhang <yong.zhang@xxxxxxxxxxxxx>
---
 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;								\
+})
+
 #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;
-- 
1.5.6.5

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