Re: [PATCH] powerpc/ftrace: Ignore ftrace locations in exit text sections

Christophe Leroy [off-list ref] writes:

Le 09/02/2024 à 08:59, Naveen N Rao a écrit :

quoted

Michael reported that we are seeing ftrace bug on bootup when KASAN is
enabled, and if we are using -fpatchable-function-entry:

...

quoted

diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index ea26665f82cf..d389dcecdb0b 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h

@@ -14,6 +14,7 @@ typedef struct func_desc func_desc_t;
  
  extern char __head_end[];
  extern char __srwx_boundary[];
+extern char _sexittext[], _eexittext[];

Should we try to at least use the same symbols as others, or best try to 
move this into include/asm-generic/sections.h, just like inittext ?

$ git grep exittext
arch/arm64/include/asm/sections.h:extern char __exittext_begin[], 
__exittext_end[];
arch/arm64/kernel/patching.c:           addr >= (unsigned 
long)__exittext_begin &&
arch/arm64/kernel/patching.c:           addr < (unsigned 
long)__exittext_end;
arch/arm64/kernel/vmlinux.lds.S:        __exittext_begin = .;
arch/arm64/kernel/vmlinux.lds.S:        __exittext_end = .;
arch/riscv/include/asm/sections.h:extern char __exittext_begin[], 
__exittext_end[];
arch/riscv/kernel/patch.c:static inline bool 
is_kernel_exittext(uintptr_t addr)
arch/riscv/kernel/patch.c:              addr >= 
(uintptr_t)__exittext_begin &&
arch/riscv/kernel/patch.c:              addr < (uintptr_t)__exittext_end;
arch/riscv/kernel/patch.c:      if (core_kernel_text(uintaddr) || 
is_kernel_exittext(uintaddr))
arch/riscv/kernel/vmlinux-xip.lds.S:    __exittext_begin = .;
arch/riscv/kernel/vmlinux-xip.lds.S:    __exittext_end = .;
arch/riscv/kernel/vmlinux.lds.S:        __exittext_begin = .;
arch/riscv/kernel/vmlinux.lds.S:        __exittext_end = .;

I'll change it to use __exittext_begin/end.

quoted

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 82010629cf88..b5efd8d7bc01 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c

@@ -27,10 +27,22 @@
  #include <asm/ftrace.h>
  #include <asm/syscall.h>
  #include <asm/inst.h>
+#include <asm/sections.h>
  
  #define	NUM_FTRACE_TRAMPS	2
  static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS];
  
+unsigned long ftrace_call_adjust(unsigned long addr)
+{
+	if (addr >= (unsigned long)_sexittext && addr < (unsigned long)_eexittext)
+		return 0;

Then arm64 has a function called is_exit_text() and riscv has 
is_kernel_exittext(). Can we refactor ?

I'd like to get the fix in and backported, so I'll take it as-is but
with the section names changed to match the other arches.

We can do further refactoring on top.

cheers