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SubjectRe: [PATCH v3 0/5] nolibc signal handling support
On Sun, Jan 08, 2023 at 07:49:30PM +0100, Willy Tarreau wrote:
> On Mon, Jan 09, 2023 at 01:31:17AM +0700, Ammar Faizi wrote:
> > I'll be pondering this code this week (to follow what actually the
> > rt_sigaction wants on i386 and arm):
> >
> >
> Seems like it could simply be a matter of sigsetsize, which is the
> first one returning -EINVAL.
> > Hopefully, I can get it sorted before the weekend.
> OK!

I couldn't dedicate much time to this, but I looked into it, and here's
my report on the progress. I didn't manage to find a proper solution to
this. But yes, you're right. It's a matter of 'sizeof(sigset_t)'.

So here is my observation. Currently, nolibc's sys.h includes this:

#include <asm/signal.h>

The definition of 'sigset_t' in that header is:

typedef unsigned long sigset_t;

On i386, 'sizeof(unsigned long)' is 4, but on x86-64 it's 8.

That is not the 'sigset_t' that the kernel wants. The kernel wants the
'sigset_t' that is in <asm-generic/signal.h>:

#define _NSIG 64
#define _NSIG_BPW __BITS_PER_LONG // this 64 on x86-64, but 32 on i386.

typedef struct {
unsigned long sig[_NSIG_WORDS];
} sigset_t;

The above struct is always 8 bytes in size. In other words:

_NSIG_WORDS == 2 on i386
_NSIG_WORDS == 1 on x86-64
sizeof(unsigned long) == 4 on i386
sizeof(unsigned long) == 8 on x86-64

Therefore, sizeof(unsigned long [_NSIG_WORDS]) is always 8 on both
architectures. That's the correct size.

I tried to #include <asm-generic/signal.h> but it conflicts with the
other 'sigset_t' definition. So I can't do that.

Why are there two different definitions of 'sigset_t'? I don't know.

I probably should read the story behind this syscall to get it
implemented right. Let me ponder this again on Monday. But at least I
tell what I have found so people can give some comments on it...

Ammar Faizi

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