Re: [REVIEW][PATCH 08/22] signal/mips: Use force_sig_fault where appropriate

From: Matt Redfearn
Date: Thu May 10 2018 - 04:04:00 EST

Hi Eric,

On 10/05/18 03:39, Eric W. Biederman wrote:
Matt Redfearn <matt.redfearn@xxxxxxxx> writes:

Hi Eric,

On 20/04/18 15:37, Eric W. Biederman wrote:
Filling in struct siginfo before calling force_sig_info a tedious and
error prone process, where once in a great while the wrong fields
are filled out, and siginfo has been inconsistently cleared.

Simplify this process by using the helper force_sig_fault. Which
takes as a parameters all of the information it needs, ensures
all of the fiddly bits of filling in struct siginfo are done properly
and then calls force_sig_info.

In short about a 5 line reduction in code for every time force_sig_info
is called, which makes the calling function clearer.

Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: James Hogan <jhogan@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
arch/mips/kernel/traps.c | 65 ++++++++++++++----------------------------------
arch/mips/mm/fault.c | 19 ++++----------
2 files changed, 23 insertions(+), 61 deletions(-)

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 967e9e4e795e..66ec4b0b484d 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -699,17 +699,11 @@ static int simulate_sync(struct pt_regs *regs, unsigned int opcode)
asmlinkage void do_ov(struct pt_regs *regs)
enum ctx_state prev_state;
- siginfo_t info;
- clear_siginfo(&info);
- info.si_signo = SIGFPE;
- info.si_code = FPE_INTOVF;
- info.si_addr = (void __user *)regs->cp0_epc;
prev_state = exception_enter();
die_if_kernel("Integer overflow", regs);
- force_sig_info(SIGFPE, &info, current);
+ force_sig_fault(SIGFPE, FPE_INTOVF, (void __user *)regs->cp0_epc, current);
@@ -722,32 +716,27 @@ asmlinkage void do_ov(struct pt_regs *regs)
void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
struct task_struct *tsk)
- struct siginfo si;
- clear_siginfo(&si);
- si.si_addr = fault_addr;
- si.si_signo = SIGFPE;
+ int si_code;

This is giving build errors in Linux next

si_code would have ended up as 0 before from the clear_siginfo(), but perhaps

And si_code 0 is not a valid si_code to use with a floating point
siginfo layout.

int si_code = FPE_FLTUNK;

Would make a more sensible default?

FPE_FLTUNK would make a more sensible default.

I seem to remember someone telling me that case can never happen in
practice so I have simply not worried about it. Perhaps I am
misremembering this.

It probably can't happen in practise - but the issue is that the kernel doesn't even compile because -Werror=maybe-uninitialized results in a build error since the compiler can't know that one of the branches will definitely be taken to set si_code.