Re: [musl] Re: Pending patches for MT-fork stuff

[Rich Felker <dalias@libc.org>]

On Wed, Mar 03, 2021 at 08:40:57AM -0600, Jesse Hathaway wrote:
> On Wed, Sep 30, 2020 at 10:55 AM Rich Felker <dalias@libc.org> wrote:
> > > > Here is the offending code:
> > > >
> > > > https://github.com/golang/go/blob/a413908dd064de6e3ea5b8d95d707a532bd3f4c8/src/runtime/signal_unix.go#L866
> > > >
> > > > It should be calling sigfillset() (from libc) to get the starting
> > > > sigset_t rather than using its own all-one-bits initializer.
> > > >
> > > > There may be other places in the runtime where the same error is made.
> > > > It looks like blockableSig (line 1132) is intended to do something
> > > > here, but has hard-coded (somewhere else) glibc knowledge rather than
> > > > probing via (libc's) sigaddset whether the signal number is valid.
> > > > This might be a preferred point to fix it at.
> 
> Unfortunately I failed to submit a bug report for this issue. However, the
> bug was reported by someone else and fixed with this commit:
> 
>   commit 49b017fe59bf628795f2c4fdbcb5db942e865fa9
>   Author: George Tsilias <tsiliasg@gmail.com>
>   Date:   Thu Jun 4 23:11:56 2020 +0300
> 
>       runtime: handle signal 34 for musl setgid
> 
>       It has been observed that setgid hangs when using cgo with musl.
>       This fix ensures that signal 34 gets handled in an appropriate way,
>       like signal 33 when using glibc.
> 
>       Fixes #39343
> 
> Unfortunately, it did not use sigaddset as you suggested, but instead hard-coded
> the signal:
> 
> diff --git a/src/runtime/sigtab_linux_generic.go
> b/src/runtime/sigtab_linux_generic.go
> index b26040b803..38d686544f 100644
> --- a/src/runtime/sigtab_linux_generic.go
> +++ b/src/runtime/sigtab_linux_generic.go
> @@ -45,7 +45,7 @@ var sigtable = [...]sigTabT{
>         /* 31 */ {_SigThrow, "SIGSYS: bad system call"},
>         /* 32 */ {_SigSetStack + _SigUnblock, "signal 32"}, /*
> SIGCANCEL; see issue 6997 */
>         /* 33 */ {_SigSetStack + _SigUnblock, "signal 33"}, /*
> SIGSETXID; see issues 3871, 9400, 12498 */
> -       /* 34 */ {_SigNotify, "signal 34"},
> +       /* 34 */ {_SigSetStack + _SigUnblock, "signal 34"}, /* musl
> SIGSYNCCALL; see issue 39343 */
>         /* 35 */ {_SigNotify, "signal 35"},
>         /* 36 */ {_SigNotify, "signal 36"},
>         /* 37 */ {_SigNotify, "signal 37"},
> diff --git a/src/runtime/sigtab_linux_mipsx.go
> b/src/runtime/sigtab_linux_mipsx.go
> index 81dd2314c5..51ef470ce7 100644
> --- a/src/runtime/sigtab_linux_mipsx.go
> +++ b/src/runtime/sigtab_linux_mipsx.go
> @@ -42,7 +42,7 @@ var sigtable = [...]sigTabT{
>         /*  31 */ {_SigNotify, "SIGXFSZ: file size limit exceeded"},
>         /*  32 */ {_SigSetStack + _SigUnblock, "signal 32"}, /*
> SIGCANCEL; see issue 6997 */
>         /*  33 */ {_SigSetStack + _SigUnblock, "signal 33"}, /*
> SIGSETXID; see issues 3871, 9400, 12498 */
> -       /*  34 */ {_SigNotify, "signal 34"},
> +       /*  34 */ {_SigSetStack + _SigUnblock, "signal 34"}, /* musl
> SIGSYNCCALL; see issue 39343 */
>         /*  35 */ {_SigNotify, "signal 35"},
>         /*  36 */ {_SigNotify, "signal 36"},
>         /*  37 */ {_SigNotify, "signal 37"},

Anyone want to submit a bug report for this (the signal numbers are
not public or stable) or should I make a note to do it?

Rich