[Valgrind-developers] compatibility with LLD

[Andrew K. <sup...@gm...>]

Hello folks,

When linking with LLD instead of binutils ld, valgrind does not see the
debug info.

I filed this bug (https://bugs.llvm.org/show_bug.cgi?id=37021) on LLD
yesterday which resulted in this conversation on the mailing list:

> It's more of a valgrind issue than an LLD issue, but you can work around
it by linking with --no-rosegment

> --rosegment puts read-only data and executable text in a single segment
and make it executable, so your read-only code becomes executable. I think
that shouldn't be a default behavior. If valgrind needs that, we can't fix
it by changing the default.

> But I can't think of a reason that valgrind needs executable data
segment. It is likely that valgrind assumes some specific segment layout
that the GNU linker creates and can't handle other layout even if it is
valid.

I had a look at readelf output and the layout of the lld-linked object file
looks sane to me.

Is there perhaps some adjustment to valgrind we can make to make it
compatible with this other linker?

Steps to reproduce:
// test.c
static int *foo(void) {
    return (int *)10000000;
}

int main(void) {
    int *x = foo();
    *x += 1;
}


// looks good with binutils ld
clang -o test test.c -g
valgrind ./test
==23250==    at 0x400597: main (test.c:7)


// with lld, valgrind does not see debug info
clang -o test test.c -g -fuse-ld=lld
valgrind ./test
==24210==    at 0x2010F7: ??? (in /home/andy/tmp/test)


Regards,
Andrew