All development is taking place on github, I'll respond there.
https://github.com/libunwind/libunwind/issues/190
Thanks
On Mon, Jun 22, 2020 at 11:58 PM Mark W. Krentel <kren...@rice.edu> wrote:
> Hi, I found a data point where libunwind 1.5-stable doesn't build.
> I started looking into this and I have a couple questions or suggestions.
> These apply to both master and 1.5-stable.
>
> (1) --enable-debug-frame doesn't build on RedHat 7.x because elf.h is
> too old. I first noticed this on aarch64 where debug-frame is turned
> on by default, but it applies anywhere with --enable-debug-frame and
> RedHat 7.x.
>
> The problem is /usr/include/elf.h is too old for libunwind 1.5 and
> doesn't define SHF_COMPRESSED. The build fails with:
>
> ../../libunwind-1.5-rc1/src/dwarf/Gfind_proc_info-lsb.c:
> In function 'load_debug_frame':
> ../../libunwind-1.5-rc1/src/dwarf/Gfind_proc_info-lsb.c:130:24:
> error: 'SHF_COMPRESSED' undeclared (first use in this function)
> if (shdr->sh_flags & SHF_COMPRESSED)
>
> This fails on RedHat 7.x, but of course, the real problem is the
> version of glibc, 2.17 on RH 7. But I haven't done the bisection to
> identify the rev where this was added.
>
> For my purposes (I've recently become the maintainer for the spack
> libunwind package, github.com/spack/spack), I have an easy workaround.
> I just require a recent elf headers as a prereq.
>
> But I was thinking you might want to add a configure test (see if
> SHF_COMPRESSED is defined in elf.h) and turn off debug-frame if not.
>
> ----------
>
> (2) On aarch64, there is a spew of warnings over the asm definition of
> unw_tdep_getcontext().
>
>
> In file included from ../include/libunwind.h:7:0,
> from mi/backtrace.c:29:
> mi/backtrace.c: In function 'unw_backtrace':
> ../include/libunwind-aarch64.h:236:5: warning: right-hand operand of
> comma expression has no effect [-Wunused-value]
> #define unw_tdep_getcontext(uc) (({ \
> ~~~~~~~~~
> unw_tdep_context_t *unw_ctx = (uc); \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> register uint64_t *unw_base __asm__ ("x0") = (uint64_t*)
> unw_ctx->uc_mcontext.regs; \
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> __asm__ __volatile__ ( \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> "stp x0, x1, [%[base], #0]\n" \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> "stp x2, x3, [%[base], #16]\n" \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ...
>
> "str x30, [%[base], #240]\n" \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> "mov x1, sp\n" \
> ~~~~~~~~~~~~~~~~
> "stp x1, x30, [%[base], #248]\n" \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> : [base] "+r" (unw_base) : : "x1", "memory"); \
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> }), 0)
> ~~^~~~
> ../include/libunwind-common.h:127:29: note: in expansion of macro
> 'unw_tdep_getcontext'
> #define unw_getcontext(uc) unw_tdep_getcontext(uc)
> ^~~~~~~~~~~~~~~~~~~
> mi/backtrace.c:71:7: note: in expansion of macro 'unw_getcontext'
> unw_getcontext (&uc);
> ^~~~~~~~~~~~~~
>
> AFAICT, the warning is harmless, but the message is pretty verbose and
> happens something like 5-6 times. So, anyone looking at the build
> will stop and wonder.
>
> It might be worthwhile to adjust the define to silence the warning.
>
> Thanks,
>
> --Mark
>
>
>
>
--
-Dave
