Syscall #82 has been implemented for 32-bit platforms in a unique way on powerpc systems. This hack will in effect guess whether the caller is expecting new select semantics or old select semantics. It does so via a guess, based off the first parameter. In new select, this parameter represents the length of a user-memory array of file descriptors, and in old select this is a pointer to an arguments structure.
The heuristic simply interprets sufficiently large values of its first parameter as being a call to old select. The following is a discussion on how this syscall should be handled. Link: https://lore.kernel.org/lkml/13737de5-0eb7-e881-9af0-163b0d29a...@csgroup.eu/ As discussed in this thread, the existence of such a hack suggests that for whatever powerpc binaries may predate glibc, it is most likely that they would have taken use of the old select semantics. x86 and arm64 both implement this syscall with oldselect semantics. Remove the powerpc implementation, and update syscall.tbl to refer to emit a reference to sys_old_select for 32-bit binaries, in keeping with how other architectures support syscall #82. Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com> --- V1 -> V2: Remove arch-specific select handler --- arch/powerpc/kernel/syscalls.c | 18 ------------------ arch/powerpc/kernel/syscalls/syscall.tbl | 2 +- .../arch/powerpc/entry/syscalls/syscall.tbl | 2 +- 3 files changed, 2 insertions(+), 20 deletions(-) diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c index 9f339bcb433d..0afbcbd50433 100644 --- a/arch/powerpc/kernel/syscalls.c +++ b/arch/powerpc/kernel/syscalls.c @@ -74,24 +74,6 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, size_t, len, return do_mmap2(addr, len, prot, flags, fd, offset, PAGE_SHIFT); } -#ifdef CONFIG_PPC32 -/* - * Due to some executables calling the wrong select we sometimes - * get wrong args. This determines how the args are being passed - * (a single ptr to them all args passed) then calls - * sys_select() with the appropriate args. -- Cort - */ -SYSCALL_DEFINE5(ppc_select, int, n, fd_set __user *, inp, - fd_set __user *, outp, fd_set __user *, exp, - struct __kernel_old_timeval __user *, tvp) -{ - if ((unsigned long)n >= 4096) - return sys_old_select((void __user *)n); - - return sys_select(n, inp, outp, exp, tvp); -} -#endif - #ifdef CONFIG_PPC64 static inline long do_ppc64_personality(unsigned long personality) { diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 59d9259dfbb5..c6cfcdf52c57 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -110,7 +110,7 @@ 79 common settimeofday sys_settimeofday compat_sys_settimeofday 80 common getgroups sys_getgroups 81 common setgroups sys_setgroups -82 32 select sys_ppc_select sys_ni_syscall +82 32 select sys_old_select sys_ni_syscall 82 64 select sys_ni_syscall 82 spu select sys_ni_syscall 83 common symlink sys_symlink diff --git a/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl b/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl index 437066f5c4b2..b4c970c9c6b1 100644 --- a/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl +++ b/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl @@ -110,7 +110,7 @@ 79 common settimeofday sys_settimeofday compat_sys_settimeofday 80 common getgroups sys_getgroups 81 common setgroups sys_setgroups -82 32 select sys_ppc_select sys_ni_syscall +82 32 select sys_old_select sys_ni_syscall 82 64 select sys_ni_syscall 82 spu select sys_ni_syscall 83 common symlink sys_symlink -- 2.34.1
