Re: [musl] [PATCH 1/3] setjmp: fix x86-64 longjmp argument adjustment

[Alexander Monakov <amonakov@ispras.ru>]

On Tue, 11 Aug 2020, Rich Felker wrote:

> Thanks! This whole series looks good and I'm applying it now.
> 
> Re: optimizing the tails, I wonder why they were ever written the way
> they were to begin with. At least the i386 one was written by me so
> there's nobody else to ask, but do you have any insight into what I
> might have been thinking?

No idea.

By the way, you should check if other 64-bit ports in musl exhibit
the same issue. The AArch64 port definitely does, for example.

Here's a standalone testcase, needs -O2 so test_lj passes its second
argument unchanged:

#include <setjmp.h>

static void test_lj(jmp_buf jb, long lv)
{
        longjmp(jb, lv);
}

int main()
{
        void (*volatile ptest)(jmp_buf, long) = 0;
        jmp_buf jb;

        int v = setjmp(jb);
        ptest = ptest ? 0 : test_lj;
        if (ptest) ptest(jb, 1l<<32);
        return !v;
}


Alexander