riscv: vdso: fix section overlapping under some conditions

lkp reported a build error, I tried the config and can reproduce
build error as below:

  VDSOLD  arch/riscv/kernel/vdso/vdso.so.dbg
ld.lld: error: section .note file range overlaps with .text
>>> .note range is [0x7C8, 0x803]
>>> .text range is [0x800, 0x1993]

ld.lld: error: section .text file range overlaps with .dynamic
>>> .text range is [0x800, 0x1993]
>>> .dynamic range is [0x808, 0x937]

ld.lld: error: section .note virtual address range overlaps with .text
>>> .note range is [0x7C8, 0x803]
>>> .text range is [0x800, 0x1993]

Fix it by setting DISABLE_BRANCH_PROFILING which will disable branch
tracing for vdso, thus avoid useless _ftrace_annotated_branch section
and _ftrace_branch section. Although we can also fix it by removing
the hardcoded .text begin address, but I think that's another story
and should be put into another patch.

Link: https://lore.kernel.org/lkml/[email protected]/#r
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Jisheng Zhang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Fixes: ad5d112 ("riscv: use vDSO common flow to reduce the latency of the time-related functions")
Cc: [email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: xhackerustc

arch/riscv/kernel/vdso/Makefile

@@ -17,6 +17,7 @@ vdso-syms += flush_icache
 obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o
 
 ccflags-y := -fno-stack-protector
+ccflags-y += -DDISABLE_BRANCH_PROFILING
 
 ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday.o += -fPIC -include $(c-gettimeofday-y)