commit 2d43cc701b96f910f50915ac4c2a0cae5deb734c upstream.
Building ppc64le_defconfig with GCC 14 fails with assembler errors:
CC fs/readdir.o
/tmp/ccdQn0mD.s: Assembler messages:
/tmp/ccdQn0mD.s:212: Error: operand out of domain (18 is not a multiple of 4)
/tmp/ccdQn0mD.s:226: Error: operand out of domain (18 is not a multiple of 4)
... [6 lines]
/tmp/ccdQn0mD.s:1699: Error: operand out of domain (18 is not a multiple of 4)
A snippet of the asm shows:
# ../fs/readdir.c:210: unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
ld 9,0(29) # MEM[(u64 *)name_38(D) + _88 * 1], MEM[(u64 *)name_38(D) + _88 * 1]
# 210 "../fs/readdir.c" 1
1: std 9,18(8) # put_user # *__pus_addr_52, MEM[(u64 *)name_38(D) + _88 * 1]
The 'std' instruction requires a 4-byte aligned displacement because
it is a DS-form instruction, and as the assembler says, 18 is not a
multiple of 4.
A similar error is seen with GCC 13 and CONFIG_UBSAN_SIGNED_WRAP=y.
The fix is to change the constraint on the memory operand to put_user(),
from "m" which is a general memory reference to "YZ".
The "Z" constraint is documented in the GCC manual PowerPC machine
constraints, and specifies a "memory operand accessed with indexed or
indirect addressing". "Y" is not documented in the manual but specifies
a "memory operand for a DS-form instruction". Using both allows the
compiler to generate a DS-form "std" or X-form "stdx" as appropriate.
Unfortunately clang doesn't support the "Y" constraint so that has to be
behind an ifdef.
Although the build error is only seen with GCC 13/14, that appears
to just be luck. The constraint has been incorrect since it was first
added.
Fixes: c20beffeec3c ("powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()")
Suggested-by: Kewen Lin <linkw@xxxxxxxxxxx>
[mpe: Drop CONFIG_PPC_KERNEL_PREFIXED ifdef for backport]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/20240529123029.146953-1-mpe@xxxxxxxxxxxxxx
---
arch/powerpc/include/asm/uaccess.h | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 6b808bcdecd5..6df110c1254e 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -186,9 +186,20 @@ do { \
: \
: label)
+#ifdef CONFIG_CC_IS_CLANG
+#define DS_FORM_CONSTRAINT "Z<>"
+#else
+#define DS_FORM_CONSTRAINT "YZ<>"
+#endif
+
#ifdef __powerpc64__
-#define __put_user_asm2_goto(x, ptr, label) \
- __put_user_asm_goto(x, ptr, label, "std")
+#define __put_user_asm2_goto(x, addr, label) \
+ asm goto ("1: std%U1%X1 %0,%1 # put_user\n" \
+ EX_TABLE(1b, %l2) \
+ : \
+ : "r" (x), DS_FORM_CONSTRAINT (*addr) \
+ : \
+ : label)
#else /* __powerpc64__ */
#define __put_user_asm2_goto(x, addr, label) \
asm_volatile_goto( \
--
2.45.1
