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2022-10-07powerpc: Don't add __powerpc_ prefix to syscall entry pointsMichael Ellerman
When using syscall wrappers the __SYSCALL_DEFINEx() and related macros add a "__powerpc_" prefix to all syscall entry points. So for example sys_mmap becomes __powerpc_sys_mmap. This risks breaking workflows and tools that expect the old naming scheme. At a minimum setting a breakpoint on eg. sys_mmap with gdb no longer works. There seems to be no compelling reason to add the "__powerpc_" prefix, other than that it follows what some other arches do (x86, arm64, s390). But unlike other arches powerpc doesn't always enable syscall wrappers, so the syscall entry points can change name depending on CONFIG options. For those reasons drop the "__powerpc_" prefix, reverting to the existing naming. Doing so reveals two prototypes in signal.h that have the incorrect type when syscall wrappers are enabled. There are already prototypes for both functions in syscalls.h, so drop the ones from signal.h. Fixes: 7e92e01b7245 ("powerpc: Provide syscall wrapper") Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221006135940.1223988-1-mpe@ellerman.id.au
2022-09-28powerpc: Provide syscall wrapperRohan McLure
Implement syscall wrapper as per s390, x86, arm64. When enabled cause handlers to accept parameters from a stack frame rather than from user scratch register state. This allows for user registers to be safely cleared in order to reduce caller influence on speculation within syscall routine. The wrapper is a macro that emits syscall handler symbols that call into the target handler, obtaining its parameters from a struct pt_regs on the stack. As registers are already saved to the stack prior to calling system_call_exception, it appears that this function is executed more efficiently with the new stack-pointer convention than with parameters passed by registers, avoiding the allocation of a stack frame for this method. On a 32-bit system, we see >20% performance increases on the null_syscall microbenchmark, and on a Power 8 the performance gains amortise the cost of clearing and restoring registers which is implemented at the end of this series, seeing final result of ~5.6% performance improvement on null_syscall. Syscalls are wrapped in this fashion on all platforms except for the Cell processor as this commit does not provide SPU support. This can be quickly fixed in a successive patch, but requires spu_sys_callback to allocate a pt_regs structure to satisfy the wrapped calling convention. Co-developed-by: Andrew Donnellan <ajd@linux.ibm.com> Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> Reviewed-by: Nicholas Piggin <npiggin@gmai.com> [mpe: Make incompatible with COMPAT to retain clearing of high bits of args] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20220921065605.1051927-22-rmclure@linux.ibm.com
2022-09-28powerpc: Use common syscall handler typeRohan McLure
Cause syscall handlers to be typed as follows when called indirectly throughout the kernel. This is to allow for better type checking. typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long); Since both 32 and 64-bit abis allow for at least the first six machine-word length parameters to a function to be passed by registers, even handlers which admit fewer than six parameters may be viewed as having the above type. Coercing syscalls to syscall_fn requires a cast to void* to avoid -Wcast-function-type. Fixup comparisons in VDSO to avoid pointer-integer comparison. Introduce explicit cast on systems with SPUs. Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20220921065605.1051927-19-rmclure@linux.ibm.com
2022-09-28powerpc: Enable compile-time check for syscall handlersRohan McLure
The table of syscall handlers and registered compatibility syscall handlers has in past been produced using assembly, with function references resolved at link time. This moves link-time errors to compile-time, by rewriting systbl.S in C, and including the linux/syscalls.h, linux/compat.h and asm/syscalls.h headers for prototypes. Reported-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20220921065605.1051927-18-rmclure@linux.ibm.com