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author | Dave Martin <Dave.Martin@arm.com> | 2017-08-01 15:35:53 +0100 |
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committer | Catalin Marinas <catalin.marinas@arm.com> | 2017-08-07 09:58:33 +0100 |
commit | 35d0e6fb4d219d64ab3b7cffef7a11a0662140f5 (patch) | |
tree | ce5ac008ec803ea479d715b84515c59c6e68ef20 /fs/exofs | |
parent | aae4e7a8bc44722fe70d58920a36916b1043195e (diff) | |
download | linux-35d0e6fb4d219d64ab3b7cffef7a11a0662140f5.tar.bz2 |
arm64: syscallno is secretly an int, make it official
The upper 32 bits of the syscallno field in thread_struct are
handled inconsistently, being sometimes zero extended and sometimes
sign-extended. In fact, only the lower 32 bits seem to have any
real significance for the behaviour of the code: it's been OK to
handle the upper bits inconsistently because they don't matter.
Currently, the only place I can find where those bits are
significant is in calling trace_sys_enter(), which may be
unintentional: for example, if a compat tracer attempts to cancel a
syscall by passing -1 to (COMPAT_)PTRACE_SET_SYSCALL at the
syscall-enter-stop, it will be traced as syscall 4294967295
rather than -1 as might be expected (and as occurs for a native
tracer doing the same thing). Elsewhere, reads of syscallno cast
it to an int or truncate it.
There's also a conspicuous amount of code and casting to bodge
around the fact that although semantically an int, syscallno is
stored as a u64.
Let's not pretend any more.
In order to preserve the stp x instruction that stores the syscall
number in entry.S, this patch special-cases the layout of struct
pt_regs for big endian so that the newly 32-bit syscallno field
maps onto the low bits of the stored value. This is not beautiful,
but benchmarking of the getpid syscall on Juno suggests indicates a
minor slowdown if the stp is split into an stp x and stp w.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'fs/exofs')
0 files changed, 0 insertions, 0 deletions