Date: Sun, 19 Nov 1995 19:35:21 +1100 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, cimaxp1!jb@werple.net.au Cc: hackers@FreeBSD.org, jb@cimlogic.com.au Subject: Re: int type in jmpbuf Message-ID: <199511190835.TAA28132@godzilla.zeta.org.au>
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>> typedef struct {
>> __type_whose_alignment_requirement_i_maximal_t _jb0;
>> char _jb1[_NOT_QUITE_THE_FULL_SIZEOF_JMP_BUF];
>> } jmp_buf[1];
>I don't understand the significance of the type (__type_whose..imal_t) for
>_jb0 vs char for _jb1. How is this different to
>typedef struct {
> char _jb0[_THE_FULL_SIZEOF_JMP_BUF];
>} jmp_buf[1];
The latter is only guaranteed to be aligned on 1-byte boundaries.
>And if the whole struct should be declared in a machine dependent file, what
>would prevent us from defining the structure from what it contains
>typedef struct {
> long reg_edx;
> long reg_ebx;
> long reg_esp;
> :
> :
>} jmp_buf[1];
>I guess the answer to this is that it is supposed to be opaque, but in my
>case I have to manually setup a jmp_buf for each user-space thread and I'd
>like a clean way of accessing the structure. Any ideas?
It's supposed to be opaque to stop that :-). You should copy setjmp.S
and adapt it. Note that it isn't possible to do preemptive context
switching for threads using only setjmp() - setjmp() doesn't preserve
all of the floating point state in FreeBSD.
Bruce
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