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authorDave Martin <Dave.Martin@arm.com>2017-08-01 15:35:53 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2017-08-07 09:58:33 +0100
commit35d0e6fb4d219d64ab3b7cffef7a11a0662140f5 (patch)
treece5ac008ec803ea479d715b84515c59c6e68ef20 /arch/arm64/kernel/signal32.c
parentaae4e7a8bc44722fe70d58920a36916b1043195e (diff)
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 'arch/arm64/kernel/signal32.c')
-rw-r--r--arch/arm64/kernel/signal32.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index c747a0fc5d7d..d98ca76cbd39 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -354,7 +354,7 @@ static int compat_restore_sigframe(struct pt_regs *regs,
/*
* Avoid compat_sys_sigreturn() restarting.
*/
- regs->syscallno = ~0UL;
+ regs->syscallno = ~0;
err |= !valid_user_regs(&regs->user_regs, current);