[musl] Re: aarch64 sigsetjmp relocation truncation bug, maybe

[Peter Williams <peter@newton.cx>]

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Of course, right after I send the email ... here's another piece of
evidence, which I think is consistent with my interpretation below.

If I simply add the following function to one of my C files:

void you_gotta_be_kidding_me(int arg)
{
    jmp_buf buf1;
    sigjmp_buf buf2;

    setjmp(buf1);
    sigsetjmp(buf2, arg);
}

... the linker error goes away. My hypothesis is/was that code like
this would encourage the linker to locate the two libc functions closer
together, so that the relocation is no longer truncated. So, it appears
that I at least have a workaround.

Peter

On Wed, 2023-09-06 at 20:46 -0400, Peter Williams wrote:
> Hello,
> 
> I'm experiencing a software issue that I think maybe, might,
> possibly, indicate a musl bug. I'm not at all familiar with the
> issues involved, but it looks like emailing this list might be my
> best bet for testing that hypothesis, so that's what I'm doing.
> Please CC me on any replies as I'm not subscribed, and accept my
> apologies if I'm way off base here.
> 
> The short answer is that I'm trying to link a large (~100 MB) static
> executable for aarch64 and getting this error out of the binutils
> linker:
> 
>   /home/rust/sysroot-aarch64/usr/lib/libc.a(sigsetjmp.lo): in function `sigsetjmp':
>   /home/buildozer/aports/main/musl/src/v1.2.3/src/signal/aarch64/sigsetjmp.s:7:(.text+0x0):
>     relocation truncated to fit: R_AARCH64_CONDBR19 against symbol `setjmp'
>     defined in .text section in /home/rust/sysroot-aarch64/usr/lib/libc.a(setjmp.lo)
> 
> If I'm understanding correctly, the complaint is that a branch in
> sigsetjmp that invokes setjmp is too far away from the definition of
> setjmp. My very handwavey idea is that maybe for some reason my
> program is causing the linker to want to locate setjmp() and
> sigsetjmp() really far away from each other. If that's right, perhaps
> it would be possible to modify the assembler code to be able to
> handle such a situation?
> 
> My build environment is extremely gnarly — I am running my build
> tools inside a cross-compiling Alpine Linux chroot that in turn runs
> inside an Ubuntu Docker container. (You don't want to know.) I can
> provide more details if needed, as well as a script that leads up to
> the error on my system, if you have CPU time to burn on the Docker
> container build. But since the error seems to be localized within my
> aarch64 "libc.a", I'm hopeful that maybe this funky environment
> doesn't actually affect the core situation here. As you might see in
> the output above, I'm using musl 1.2.3.
> 
> Thanks for any insight,
> 
> Peter
> 


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