[LLVMdev] built-in longjmp and setjmp

[Akira Hatanaka]

Okay. I understand builtin functions do not have to behave exactly the same
way as standard library functions. What I wanted to know is what should the
code generated by llvm (clang + llc) look like (I am working on the Mips
back-end now). I guess there should be a behavior users expect to see who
are using __builtin_setjmp/longjmp even they aren't the same as library
functions. If the code generated by arm-darwin is acceptable, does it mean
that you can freely move code that accesses a global variable above the call
to setjmp?

On Wed, Apr 27, 2011 at 2:03 PM, Jim Grosbach <grosbach at apple.com> wrote:

> There is no C standard to follow for these builtins. You are expecting them
> to behave as if they were the standard library calls. They are not
> equivalent and the naming similarity is an unfortunate historical artifact.
> Use the standard library functions instead.
>
> -Jim
>
> On Apr 27, 2011, at 1:22 PM, Akira Hatanaka wrote:
>
> > I declared gi2 as "volatile" and I think gi2 is still incremented once.
> > Here is a snippet of the code. Line 39 - 42 increments gi2.
> >
> > According to the standard, shouldn't ++gi2 be executed twice regardless
> of whether gi2 is volatile or not? Isn't the missing chain from
> EH_SJLJ_SETJMP node to load/store nodes that access gi2 causing this problem
> (please see attached file in my previous email)?
> >
> > # line 39 - 47
> >  ldr r1, LCPI1_1
> >  ldr r2, [r1]
> >  add r2, r2, #1
> >  str r2, [r1]
> >  add r4, pc, #8              @ eh_setjmp begin
> >  str r4, [r0, #4]
> >  mov r0, #0
> >  add pc, pc, #0
> >  mov r0, #1                  @ eh_setjmp end
> >
> >  ...
> > LCPI1_1:
> >   .long _gi2
> >   .align  2
> >
> >
> > On Wed, Apr 27, 2011 at 11:38 AM, Akira Hatanaka <ahatanak at gmail.com>
> wrote:
> > I have another basic question about setjmp/longjmp.
> >
> > When I compile and run the following program, is it expected that global
> variable gi2 will be incremented twice? It seems that the code generated
> with clang and llc increments it only once (line 37-43 of attached file).
> >
> > $ clang setjmp6.c -o setjmp6.arm.ll -emit-llvm -O3 -S -ccc-host-triple
> arm-unknown-darwin -ccc-clang-archs arm
> > $ llc setjmp6.arm.ll -o setjmp6.arm.s
> >
> >
> > #include <stdio.h>
> > #include <stdlib.h>
> > void *buf[20];
> >
> > int gi2 = 0;
> >
> >
> > void __attribute__ ((noinline)) sub2 (void)
> > {
> >   __builtin_longjmp (buf, 1);
> >
> > }
> >
> > int
> > main (int argc, char **argv)
> > {
> >   int n = atoi (argv[1]);
> >   int r = __builtin_setjmp (buf);
> >   ++gi2;
> >
> >   if (r)
> >     {
> >       printf ("setjmp %d\n", n + gi2);
> >       return 0;
> >     }
> >
> >   sub2 ();
> >
> >   return 0;
> > }
> >
> >
> > On Wed, Apr 13, 2011 at 10:05 AM, Jakob Stoklund Olesen <stoklund at 2pi.dk>
> wrote:
> >
> > On Apr 13, 2011, at 9:51 AM, Akira Hatanaka wrote:
> >
> > > int
> > > main (int argc, char** argv)
> > > {
> > >   int n = atoi(argv[1]), r;
> > >
> > >   if ((r = setjmp (buf)))
> > >     {
> > >       printf("n = %d\n", n);
> > >       return 0;
> > >     }
> >
> >
> > /jakob
> >
> >
> >
> > <f.s>_______________________________________________
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>
>
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