linux-toradex.git/arch/riscv/kernel/mcount-dyn.S, branch v6.7-rc1

riscv: Use SYM_*() assembly macros instead of deprecated ones

2023-11-06T17:42:47+00:00

ENTRY()/END()/WEAK() macros are deprecated and we should make use of the
new SYM_*() macros [1] for better annotation of symbols. Replace the
deprecated ones with the new ones and fix wrong usage of END()/ENDPROC()
to correctly describe the symbols.

[1] https://docs.kernel.org/core-api/asm-annotations.html

Signed-off-by: Clément Léger 
Reviewed-by: Andrew Jones 
Link: https://lore.kernel.org/r/20231024132655.730417-3-cleger@rivosinc.com
Signed-off-by: Palmer Dabbelt

riscv: entry: Consolidate general regs saving/restoring

2023-03-23T15:47:03+00:00

Consolidate the saving/restoring GPs (except zero, ra, sp, gp,
tp and t0) into save_from_x6_to_x31/restore_from_x6_to_x31 macros.

No functional change intended.

Signed-off-by: Jisheng Zhang 
Reviewed-by: Guo Ren 
Reviewed-by: Björn Töpel 
Tested-by: Guo Ren 
Signed-off-by: Guo Ren 
Link: https://lore.kernel.org/r/20230222033021.983168-8-guoren@kernel.org
Signed-off-by: Palmer Dabbelt

riscv: ftrace: Reduce the detour code size to half

2023-02-15T18:58:21+00:00

Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.

Before the patch:
:
 0: REG_S  ra, -SZREG(sp)
 4: auipc  ra, ?
 8: jalr   ?(ra)
12: REG_L  ra, -SZREG(sp)
 (func_boddy)

After the patch:
:
 0: auipc  t0, ?
 4: jalr   t0, ?(t0)
 (func_boddy)

This patch not just reduces the size of detour code, but also fixes an
important issue:

An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.

In this case, the trampoline (ftrace_regs_caller) would not return to
 but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.

This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.

Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai 
Signed-off-by: Song Shuai 
Signed-off-by: Guo Ren 
Signed-off-by: Guo Ren 
Cc: Evgenii Shatokhin 
Reviewed-by: Evgenii Shatokhin 
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt

riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT

2021-01-14T23:09:05+00:00

This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].

Before the patch, we used mcount for detour:
:
	addi sp,sp,-16
	sd   ra,8(sp)
	sd   s0,0(sp)
	addi s0,sp,16
	mv   a5,ra
	mv   a0,a5
	auipc ra,0x0 -> nop
	jalr  -296(ra) <_mcount@plt> ->nop
	...

After the patch, we use nop call site area for detour:
:
	nop -> REG_S ra, -SZREG(sp)
	nop -> auipc ra, 0x?
	nop -> jalr ?(ra)
	nop -> REG_L ra, -SZREG(sp)
	...

The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.

[1] https://www.linuxplumbersconf.org/event/7/contributions/807/

Signed-off-by: Guo Ren 
Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add DYNAMIC_FTRACE_WITH_REGS support

2018-04-03T02:59:13+00:00

Cc: Greentime Hu 
Signed-off-by: Alan Kao 
Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add ARCH_SUPPORTS_FTRACE_OPS support

2018-04-03T02:59:12+00:00

Cc: Greentime Hu 
Signed-off-by: Alan Kao 
Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add dynamic function graph tracer support

2018-04-03T02:59:12+00:00

Once the function_graph tracer is enabled, a filtered function has the
following call sequence:

* ftracer_caller         ==> on/off by ftrace_make_call/ftrace_make_nop
* ftrace_graph_caller
* ftrace_graph_call      ==> on/off by ftrace_en/disable_ftrace_graph_caller
* prepare_ftrace_return

Considering the following DYNAMIC_FTRACE_WITH_REGS feature, it would be
more extendable to have a ftrace_graph_caller function, instead of
calling prepare_ftrace_return directly in ftrace_caller.

Cc: Greentime Hu 
Signed-off-by: Alan Kao 
Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add dynamic function tracer support

2018-04-03T02:59:12+00:00

We now have dynamic ftrace with the following added items:

* ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c)
  The two functions turn each recorded call site of filtered functions
  into a call to ftrace_caller or nops

* ftracce_update_ftrace_func (in kernel/ftrace.c)
  turns the nops at ftrace_call into a call to a generic entry for
  function tracers.

* ftrace_caller (in kernel/mcount-dyn.S)
  The entry where each _mcount call sites calls to once they are
  filtered to be traced.

Also, this patch fixes the semantic problems in mcount.S, which will be
treated as only a reference implementation once we have the dynamic
ftrace.

Cc: Greentime Hu 
Signed-off-by: Alan Kao 
Signed-off-by: Palmer Dabbelt