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authorNicolas Pitre <nico@fluxnic.net>2010-08-26 23:10:50 -0400
committerNicolas Pitre <nicolas.pitre@linaro.org>2010-10-01 22:35:19 -0400
commitec706dab290c486837d4a825870ab052bf200279 (patch)
treeba9437df27ea98feedb7409559a18d7870220688 /arch/arm/include/asm/mmu_context.h
parent70c70d97809c3cdb8ff04f38ee3718c5385a2a4d (diff)
ARM: add a vma entry for the user accessible vector page
The kernel makes the high vector page visible to user space. This page contains (amongst others) small code segments that can be executed in user space. Make this page visible through ptrace and /proc/<pid>/mem in order to let gdb perform code parsing needed for proper unwinding. For example, the ERESTART_RESTARTBLOCK handler actually has a stack frame -- it returns to a PC value stored on the user's stack. To unwind after a "sleep" system call was interrupted twice, GDB would have to recognize this situation and understand that stack frame layout -- which it currently cannot do. We could fix this by hard-coding addresses in the vector page range into GDB, but that isn't really portable as not all of those addresses are guaranteed to remain stable across kernel releases. And having the gdb process make an exception for this page and get content from its own address space for it looks strange, and it is not future proof either. Being located above PAGE_OFFSET, this vma cannot be deleted by user space code. Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Diffstat (limited to 'arch/arm/include/asm/mmu_context.h')
-rw-r--r--arch/arm/include/asm/mmu_context.h29
1 files changed, 28 insertions, 1 deletions
diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index a0b3cac0547..71605d9f8e4 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -18,7 +18,6 @@
#include <asm/cacheflush.h>
#include <asm/cachetype.h>
#include <asm/proc-fns.h>
-#include <asm-generic/mm_hooks.h>
void __check_kvm_seq(struct mm_struct *mm);
@@ -134,4 +133,32 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
#define deactivate_mm(tsk,mm) do { } while (0)
#define activate_mm(prev,next) switch_mm(prev, next, NULL)
+/*
+ * We are inserting a "fake" vma for the user-accessible vector page so
+ * gdb and friends can get to it through ptrace and /proc/<pid>/mem.
+ * But we also want to remove it before the generic code gets to see it
+ * during process exit or the unmapping of it would cause total havoc.
+ * (the macro is used as remove_vma() is static to mm/mmap.c)
+ */
+#define arch_exit_mmap(mm) \
+do { \
+ struct vm_area_struct *high_vma = find_vma(mm, 0xffff0000); \
+ if (high_vma) { \
+ BUG_ON(high_vma->vm_next); /* it should be last */ \
+ if (high_vma->vm_prev) \
+ high_vma->vm_prev->vm_next = NULL; \
+ else \
+ mm->mmap = NULL; \
+ rb_erase(&high_vma->vm_rb, &mm->mm_rb); \
+ mm->mmap_cache = NULL; \
+ mm->map_count--; \
+ remove_vma(high_vma); \
+ } \
+} while (0)
+
+static inline void arch_dup_mmap(struct mm_struct *oldmm,
+ struct mm_struct *mm)
+{
+}
+
#endif