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Subject[s390x] Patch for execve with a mode switch
If I boot an s390x kernel over a 31 bit userland, /sbin/init segfaults
in the dynamic linker. This happens because mm->free_area_cache
is set with TASK_UNMAPPED_BASE macro, which needs the TIF_31BIT
set right. Setting TIF_31BIT in ELF_PLAT_INIT is way too late
for this.

The patch below basically ports what sparc64 does to s390x,
according to the Andrew Morton's comment in fs/binfmt_elf.c.
To tell the truth, I actually use equivalent of this on 2.4,
but I think it's important to get stock 2.5 right.

Martin, please consider and let me know what you think.

Greetings,
-- Pete

--- linux-2.5.64/arch/s390x/kernel/binfmt_elf32.c 2003-03-04 21:34:14.000000000 -0800
+++ linux-2.5.64-sparc/arch/s390x/kernel/binfmt_elf32.c 2003-03-15 16:17:34.000000000 -0800
@@ -39,7 +39,6 @@
#define ELF_PLAT_INIT(_r) \
do { \
_r->gprs[14] = 0; \
- set_thread_flag(TIF_31BIT); \
} while(0)

#define USE_ELF_CORE_DUMP
@@ -87,6 +86,8 @@

#define SET_PERSONALITY(ex, ibcs2) \
do { \
+ if ((current_thread_info()->flags & _TIF_32BIT) == 0) \
+ set_thread_flag(TIF_ABI_PENDING); \
if (ibcs2) \
set_personality(PER_SVR4); \
else if (current->personality != PER_LINUX32) \
--- linux-2.5.64/arch/s390x/kernel/process.c 2003-03-04 21:34:14.000000000 -0800
+++ linux-2.5.64-sparc/arch/s390x/kernel/process.c 2003-03-15 16:02:19.000000000 -0800
@@ -156,9 +156,14 @@

void flush_thread(void)
{
+ struct thread_info *t = current_thread_info();
+ struct task_struct *tsk = t->task;

- current->used_math = 0;
- clear_tsk_thread_flag(current, TIF_USEDFPU);
+ if (t->flags & _TIF_ABI_PENDING)
+ t->flags ^= (_TIF_ABI_PENDING | _TIF_32BIT);
+
+ tsk->used_math = 0;
+ clear_tsk_thread_flag(tsk, TIF_USEDFPU);
}

void release_thread(struct task_struct *dead_task)
--- linux-2.5.64/include/asm-s390x/elf.h 2003-03-04 21:34:43.000000000 -0800
+++ linux-2.5.64-sparc/include/asm-s390x/elf.h 2003-03-15 16:22:04.000000000 -0800
@@ -39,7 +39,6 @@
#define ELF_PLAT_INIT(_r) \
do { \
_r->gprs[14] = 0; \
- clear_thread_flag(TIF_31BIT); \
} while(0)

#define USE_ELF_CORE_DUMP
@@ -79,11 +78,12 @@
#ifdef __KERNEL__
#define SET_PERSONALITY(ex, ibcs2) \
do { \
+ if (current_thread_info()->flags & _TIF_32BIT) \
+ set_thread_flag(TIF_ABI_PENDING); \
if (ibcs2) \
set_personality(PER_SVR4); \
else if (current->personality != PER_LINUX32) \
set_personality(PER_LINUX); \
- clear_thread_flag(TIF_31BIT); \
} while (0)
#endif

--- linux-2.5.64/include/asm-s390x/thread_info.h 2003-03-04 21:34:43.000000000 -0800
+++ linux-2.5.64-sparc/include/asm-s390x/thread_info.h 2003-03-15 16:04:23.000000000 -0800
@@ -74,6 +74,7 @@
#define TIF_SIGPENDING 2 /* signal pending */
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
#define TIF_RESTART_SVC 4 /* restart svc with new svc number */
+#define TIF_ABI_PENDING 11 /* flush_thread has to switch ABI */
#define TIF_USEDFPU 16 /* FPU was used by this task this quantum (SMP) */
#define TIF_POLLING_NRFLAG 17 /* true if poll_idle() is polling
TIF_NEED_RESCHED */
@@ -84,6 +85,7 @@
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
#define _TIF_RESTART_SVC (1<<TIF_RESTART_SVC)
+#define _TIF_ABI_PENDING (1<<TIF_ABI_PENDING)
#define _TIF_USEDFPU (1<<TIF_USEDFPU)
#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
#define _TIF_31BIT (1<<TIF_31BIT)
-
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