random: vDSO: avoid call to memset() when zeroing reserved parameter

After a recent change in LLVM [1], builds with the random vDSO
implementation, such as PowerPC and RISC-V, fail when checking the

random: vDSO: avoid call to memset() when zeroing reserved parameter

After a recent change in LLVM [1], builds with the random vDSO
implementation, such as PowerPC and RISC-V, fail when checking the vDSO:

arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not supported
arch/riscv/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported

memset() is now generated when zeroing params->reserved for some builds
because LLVM has an optimization (now run in more instances) that can
recognize at compile time when it is assigning a static value to a
contiguous area of memory and turn that into a call to memset(). Both
clang and GCC assume memset() is always available [2].

Clang has an internal fiddly hook, -max-store-memset, which we can set
to a high number, to disable generating out of line memset calls [3].
Similarly, GCC has -finline-stringops=memset to do the same [4], should
this issue ever hit future version of GCC. While these options wouldn't
make sense for normal kernel code, it is fine for the extremely limited
and intentionally compact vDSO code.

Link: https://github.com/llvm/llvm-project/commit/90cebef1411617fc3eedd359bdf00cb44b1c2439 [1]
Link: https://gcc.gnu.org/onlinedocs/gcc-16.2.0/gcc/Standards.html#index-ffreestanding [2]
Link: https://github.com/llvm/llvm-project/commit/b28eeb28bea39148738dc375e8a97072a1907e64 [3]
Link: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-finline-stringops [4]
Closes: https://github.com/ClangBuiltLinux/linux/issues/2183
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

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s390/vdso: Pass --eh-frame-hdr to the linker

Commit 2b2a25845d53 ("s390/vdso: Use $(LD) instead of $(CC) to link
vDSO") accidentally broke the GNU_EH_FRAME program table entry in
the vDSO, causing i

s390/vdso: Pass --eh-frame-hdr to the linker

Commit 2b2a25845d53 ("s390/vdso: Use $(LD) instead of $(CC) to link
vDSO") accidentally broke the GNU_EH_FRAME program table entry in
the vDSO, causing it to be empty:

$ readelf --program-headers arch/s390/kernel/vdso/vdso.so
...
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
...
GNU_EH_FRAME 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x8
...

Originally, the compiler would implicitly add --eh-frame-hdr when
invoking the linker, but when this Makefile was converted from invoking
the linker via the compiler, to invoking it directly, the option was
missed.

This is the s390 variant of x86 commit cd01544a268a ("x86/vdso: Pass
--eh-frame-hdr to the linker").

Fixes: 2b2a25845d53 ("s390/vdso: Use $(LD) instead of $(CC) to link vDSO")
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

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s390/vdso: Disable kstack erase

For some reason gcc 8, 9, 10, and 11 generate a dynamic relocation in
vdso.so.dbg if CONFIG_KSTACK_ERASE is enabled:

>> arch/s390/kernel/vdso/vdso.so.dbg: dynamic re

s390/vdso: Disable kstack erase

For some reason gcc 8, 9, 10, and 11 generate a dynamic relocation in
vdso.so.dbg if CONFIG_KSTACK_ERASE is enabled:

>> arch/s390/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported
make[3]: *** [arch/s390/kernel/vdso/Makefile:54: arch/s390/kernel/vdso/vdso.so.dbg] Error 1

$ readelf -rW arch/s390/kernel/vdso/vdso.so.dbg

Relocation section '.rela.dyn' at offset 0x15c0 contains 1 entry:
Offset Info Type Symbol's Value Symbol's Name + Addend
00000000000015f0 000000010000000b R_390_JMP_SLOT 0000000000000000 __sanitizer_cov_stack_depth + 0

Add $(DISABLE_KSTACK_ERASE) to vdso compile flags to fix this.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202601070505.xQcLr5KV-lkp@intel.com/
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

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s390/vdso: Get rid of -m64 flag handling

The compiler/assembler flag -m64 is added and removed at two locations.
This pointless exercise is a leftover to keep the 31 and 64 bit vdso
Makefiles as sym

s390/vdso: Get rid of -m64 flag handling

The compiler/assembler flag -m64 is added and removed at two locations.
This pointless exercise is a leftover to keep the 31 and 64 bit vdso
Makefiles as symmetrical as possible. Given that the 31 bit vdso code
does not exist anymore, remove the -m64 flag handling.

Suggested-by: Jens Remus <jremus@linux.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

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s390/vdso: Rename vdso64 to vdso

Since compat is gone there is only a 64 bit vdso left.
Remove the superfluous "64" suffix everywhere.

Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by:

s390/vdso: Rename vdso64 to vdso

Since compat is gone there is only a 64 bit vdso left.
Remove the superfluous "64" suffix everywhere.

Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

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