What [Vectors] means in perf top report？ - vector

Question

I was using perf top to profile a process which running on arm-linux, and the result shown like below:
4.27% [vectors] [.] 0x00000fc4
3.84% [kernel] [k] _raw_spin_unlock_irqrestore
2.30% [kernel] [k] _raw_spin_unlock_irq
1.94% libc-2.20.so [.] 0x0007c35c
1.91% [vectors] [.] 0x00000fd8
1.56% libGLESv2.so.1.9.6.0 [.] 0x0003a5e0
1.34% libGLESv2.so.1.9.6.0 [.] 0x0003a5cc
0.91% [omapdrm_pvr] [k] _SegmentListInsert
0.87% libpthread-2.20.so [.] 0x0000aee4
0.82% libc-2.20.so [.] 0x00075464
0.76% libc-2.20.so [.] 0x0007767c
0.48% libpthread-2.20.so [.] 0x000094dc
0.46% libv8.so.4 [.] 0x0017a058
0.46% libGLESv2.so.1.9.6.0 [.] 0x0003a420
0.43% [kernel] [k] do_nanosleep
0.41% [kernel] [k] __copy_from_user
0.40% libc-2.20.so [.] 0x0007d8a4
0.40% libpthread-2.20.so [.] 0x00009480
0.39% [kernel] [k] do_vfp
0.39% librender_engine.so [.] 0x004d3ff8
I am wondering what [vectros] may stand for? as I know, it's not a kernel module, however, 0x00000fc4 is a low-end address which should never be used, besides that, 0x00000fc4 seems like the address of arm exception vectors.
any comment is welcomed.

Answer 1

This [vectors] is for arm memory range of vectors page, the name is defined in aarch32_setup_vectors_page function of arch/arm64/kernel/vdso.c
#define AARCH32_VECTORS_BASE 0xffff0000
....
int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp)
{
...
unsigned long addr = AARCH32_VECTORS_BASE;
static const struct vm_special_mapping spec = {
.name = "[vectors]",
.pages = vectors_page,
};
...
current->mm->context.vdso = (void *)addr;
/* Map vectors page at the high address. */
ret = _install_special_mapping(mm, addr, PAGE_SIZE,
VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYEXEC,
&spec);
...
}
and in arch_vma_name of arch/arm/kernel/process.c
/*
* The vectors page is always readable from user space for the
* atomic helpers. Insert it into the gate_vma so that it is visible
* through ptrace and /proc/<pid>/mem.
*/
static struct vm_area_struct gate_vma = {
.vm_start = 0xffff0000,
.vm_end = 0xffff0000 + PAGE_SIZE,
.vm_flags = VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYEXEC,
};
...
const char *arch_vma_name(struct vm_area_struct *vma)
{
return is_gate_vma(vma) ? "[vectors]" : NULL;
}
I'm not sure that perf will show correct address for profiling samples in this area, it may be offset inside the section...
Another question about arm's vector page: Vectors page mapping in linux for ARM
"The Exception Vector Table" on arm32 is mapped to 0xffff0000, according to https://doar-e.github.io/blog/2014/04/30/corrupting-arm-evt/
You may check output of cat /proc/self/maps on the platform and dump the page from 0xffff0000 offset with gdb x/1024wx 0xffff0000.
Presentation about newer vdso on arm64 https://blog.linuxplumbersconf.org/2016/ocw/system/presentations/3711/original/LPC_vDSO.pdf