linux-kernel - [RFC PATCH] powerpc/vdso: Should VDSO64 functions be flagged as functions like VDSO32 ?

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Message-ID: <6fa86f3de610ffc180ae0f5dbd511453e7473b36.1726208058.git.christophe.leroy@csgroup.eu>
Date: Fri, 13 Sep 2024 08:14:33 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Naveen N Rao <naveen@...nel.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: [RFC PATCH] powerpc/vdso: Should VDSO64 functions be flagged as functions like VDSO32 ?

On powerpc64 as shown below by readelf, vDSO functions symbols have
type NOTYPE.

$ powerpc64-linux-gnu-readelf -a arch/powerpc/kernel/vdso/vdso64.so.dbg
ELF Header:
  Magic:   7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF64
  Data:                              2's complement, big endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              DYN (Shared object file)
  Machine:                           PowerPC64
  Version:                           0x1
...

Symbol table '.dynsym' contains 12 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
...
     1: 0000000000000524    84 NOTYPE  GLOBAL DEFAULT    8 __[...]@@LINUX_2.6.15
...
     4: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LINUX_2.6.15
     5: 00000000000006c0    48 NOTYPE  GLOBAL DEFAULT    8 __[...]@@LINUX_2.6.15

Symbol table '.symtab' contains 56 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
...
    45: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LINUX_2.6.15
    46: 00000000000006c0    48 NOTYPE  GLOBAL DEFAULT    8 __kernel_getcpu
    47: 0000000000000524    84 NOTYPE  GLOBAL DEFAULT    8 __kernel_clock_getres

To overcome that, commit ba83b3239e65 ("selftests: vDSO: fix vDSO
symbols lookup for powerpc64") was proposed to make selftests also
look for NOTYPE symbols, but is it the correct fix ?

VDSO32 functions are flagged as functions, why not VDSO64 functions ?
Is it because VDSO functions are not traditional C functions using
the standard API ? But it is exactly the same for VDSO32 functions,
allthough they are flagged as functions.

So lets flag them as functions and revert the selftest change.

What's your opinion on that ?

It predates git kernel history and both VDSO32 and VDSO64 were brough by
arch/ppc64/ with that difference already.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
commit ba83b3239e65 is in random git tree at the moment : https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?id=ba83b3239e657469709d15dcea5f9b65bf9dbf34
On the list at : https://lore.kernel.org/lkml/fc1a0862516b1e11b336d409f2cb8aab10a97337.1725020674.git.christophe.leroy@csgroup.eu/T/#u
---
 arch/powerpc/include/asm/vdso.h           | 1 +
 tools/testing/selftests/vDSO/parse_vdso.c | 3 +--
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/vdso.h b/arch/powerpc/include/asm/vdso.h
index 7650b6ce14c8..8d972bc98b55 100644
--- a/arch/powerpc/include/asm/vdso.h
+++ b/arch/powerpc/include/asm/vdso.h
@@ -25,6 +25,7 @@ int vdso_getcpu_init(void);
 #ifdef __VDSO64__
 #define V_FUNCTION_BEGIN(name)		\
 	.globl name;			\
+	.type name,@function; 		\
 	name:				\
 
 #define V_FUNCTION_END(name)		\
diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
index d9ccc5acac18..4ae417372e9e 100644
--- a/tools/testing/selftests/vDSO/parse_vdso.c
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -216,8 +216,7 @@ void *vdso_sym(const char *version, const char *name)
 		ELF(Sym) *sym = &vdso_info.symtab[chain];
 
 		/* Check for a defined global or weak function w/ right name. */
-		if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC &&
-		    ELF64_ST_TYPE(sym->st_info) != STT_NOTYPE)
+		if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
 			continue;
 		if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&
 		    ELF64_ST_BIND(sym->st_info) != STB_WEAK)
-- 
2.44.0