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@gcc.gnu.org [mpe: Drop CONFIG_PPC_KERNEL_PREFIXED ifdef for backport] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20240529123029.146953-1-mpe@ellerman.id.au --- 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 b2680070d65d..6013a7fc74ba 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -90,9 +90,20 @@ __pu_failed: \ : \ : 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( \