linux-kernel - [PATCH] powerpc: align syscall table for ppc32

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Date:   Sun, 21 Aug 2022 01:51:29 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kbuild@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] powerpc: align syscall table for ppc32

Christophe Leroy reported that commit 7b4537199a4a ("kbuild: link
symbol CRCs at final link,  removing CONFIG_MODULE_REL_CRCS") broke
mpc85xx_defconfig + CONFIG_RELOCATABLE=y.

    LD      vmlinux
    SYSMAP  System.map
    SORTTAB vmlinux
    CHKREL  vmlinux
  WARNING: 451 bad relocations
  c0b312a9 R_PPC_UADDR32     .head.text-0x3ff9ed54
  c0b312ad R_PPC_UADDR32     .head.text-0x3ffac224
  c0b312b1 R_PPC_UADDR32     .head.text-0x3ffb09f4
  c0b312b5 R_PPC_UADDR32     .head.text-0x3fe184dc
  c0b312b9 R_PPC_UADDR32     .head.text-0x3fe183a8
      ...

The compiler emits a bunch of R_PPC_UADDR32, which is not supported by
arch/powerpc/kernel/reloc_32.S.

The reason is there exists an unaligned symbol.

  $ powerpc-linux-gnu-nm -n vmlinux
    ...
  c0b31258 d spe_aligninfo
  c0b31298 d __func__.0
  c0b312a9 D sys_call_table
  c0b319b8 d __func__.0

Commit 7b4537199a4a is not the root cause. Even before that, I can
reproduce the same issue for mpc85xx_defconfig + CONFIG_RELOCATABLE=y
+ CONFIG_MODVERSIONS=n.

It is just that nobody did not notice it because when CONFIG_MODVERSIONS
is enabled, a __crc_* symbol inserted before sys_call_table was hiding
the unalignment issue.

I checked the commit history, but I could not understand commit
46b45b10f142 ("[POWERPC] Align the sys_call_table").

It said 'Our _GLOBAL macro does a ".align 2" so the alignment is fine
for 32 bit'. I checked the _GLOBAL in include/asm-powerpc/ppc_asm.h
at that time. _GLOBAL specifies ".align 2" for ppc64, but no .align
for ppc32.

Commit c857c43b34ec ("powerpc: Don't use a function descriptor for
system call table") removed _GLOBAL from the syscall table.

Anyway, adding alignment to the syscall table for ppc32 fixes the issue.

I am not giving Fixes tag because I do not know since when it has been
broken, but presumably it has been for a long while.

Link: https://lore.kernel.org/lkml/38605f6a-a568-f884-f06f-ea4da5b214f0@csgroup.eu/
Reported-by: Christophe Leroy <christophe.leroy@...roup.eu>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 arch/powerpc/kernel/systbl.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/systbl.S b/arch/powerpc/kernel/systbl.S
index cb3358886203..6c1db3b6de2d 100644
--- a/arch/powerpc/kernel/systbl.S
+++ b/arch/powerpc/kernel/systbl.S
@@ -18,6 +18,7 @@
 	.p2align	3
 #define __SYSCALL(nr, entry)	.8byte entry
 #else
+	.p2align	2
 #define __SYSCALL(nr, entry)	.long entry
 #endif

-- 
2.34.1