Re: [PATCH v4 4/7] coroutine: add libucontext as external library

[Philippe Mathieu-Daudé]

Hi Joelle,

On 11/8/20 6:26 AM, Joelle van Dyne wrote:
> iOS does not support ucontext natively for aarch64 and the sigaltstack is
> also unsupported (even worse, it fails silently, see:
> https://openradar.appspot.com/13002712 )
> 
> As a workaround we include a library implementation of ucontext and add it
> as a build option.
> 
> Signed-off-by: Joelle van Dyne <j@getutm.app>
> ---
>  configure                 | 23 ++++++++++++++++++++---
>  meson.build               | 28 +++++++++++++++++++++++++++-
>  util/coroutine-ucontext.c |  9 +++++++++
>  .gitmodules               |  3 +++
>  libucontext               |  1 +
>  meson_options.txt         |  2 ++
>  6 files changed, 62 insertions(+), 4 deletions(-)
>  create mode 160000 libucontext
...

> diff --git a/meson.build b/meson.build
> index 8894171bd1..e62324d5ac 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -1259,9 +1259,34 @@ if not fdt.found() and fdt_required.length() > 0
>    error('fdt not available but required by targets ' + ', 
> '.join(fdt_required))
>  endif
>  
> +ucontext = not_found
> +if get_option('ucontext').enabled()
> +  if not fs.is_dir(meson.current_source_dir() / 'libucontext/arch' / cpu)
> +    error('libucontext is wanted but not implemented for host ' + cpu)
> +  endif
> +  arch = host_machine.cpu()
> +  ucontext_cargs = ['-DG_LOG_DOMAIN="ucontext"', '-DCUSTOM_IMPL']
> +  ucontext_files = [
> +    'libucontext/arch' / arch / 'getcontext.S',
> +    'libucontext/arch' / arch / 'setcontext.S',
> +    'libucontext/arch' / arch / 'makecontext.c',
> +    'libucontext/arch' / arch / 'startcontext.S',
> +    'libucontext/arch' / arch / 'swapcontext.S',
> +  ]
> +
> +  ucontext_inc = include_directories('libucontext/include')
> +  libucontext = static_library('ucontext',
> +                               sources: ucontext_files,
> +                               c_args: ucontext_cargs,
> +                               include_directories: ucontext_inc)
> +  ucontext = declare_dependency(link_with: libucontext,
> +                                include_directories: ucontext_inc)
> +endif
> +
>  config_host_data.set('CONFIG_CAPSTONE', capstone.found())
>  config_host_data.set('CONFIG_FDT', fdt.found())
>  config_host_data.set('CONFIG_SLIRP', slirp.found())
> +config_host_data.set('CONFIG_LIBUCONTEXT', ucontext.found())
>  
>  #####################
>  # Generated sources #
> @@ -1477,7 +1502,7 @@ util_ss.add_all(trace_ss)
>  util_ss = util_ss.apply(config_all, strict: false)
>  libqemuutil = static_library('qemuutil',
>                               sources: util_ss.sources() + stub_ss.sources() 
> + genh,
> -                             dependencies: [util_ss.dependencies(), m, glib, 
> socket, malloc])
> +                             dependencies: [util_ss.dependencies(), m, glib, 
> socket, malloc, ucontext])
>  qemuutil = declare_dependency(link_with: libqemuutil,
>                                sources: genh + version_res)
>  
> @@ -2135,6 +2160,7 @@ if targetos == 'windows'
>    summary_info += {'QGA MSI support':   
> config_host.has_key('CONFIG_QGA_MSI')}
>  endif
>  summary_info += {'seccomp support':   config_host.has_key('CONFIG_SECCOMP')}
> +summary_info += {'libucontext support': ucontext.found()}
>  summary_info += {'coroutine backend': 
> config_host['CONFIG_COROUTINE_BACKEND']}
>  summary_info += {'coroutine pool':    config_host['CONFIG_COROUTINE_POOL'] 
> == '1'}
>  summary_info += {'debug stack usage': 
> config_host.has_key('CONFIG_DEBUG_STACK_USAGE')}
> diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c
> index 904b375192..1e1dd43512 100644
> --- a/util/coroutine-ucontext.c
> +++ b/util/coroutine-ucontext.c
> @@ -23,7 +23,16 @@
>  #undef _FORTIFY_SOURCE
>  #endif
>  #include "qemu/osdep.h"
> +#if defined(CONFIG_LIBUCONTEXT)
> +#include <libucontext.h>
> +#define ucontext_t libucontext_ucontext_t
> +#define getcontext libucontext_getcontext
> +#define setcontext libucontext_setcontext
> +#define swapcontext libucontext_swapcontext
> +#define makecontext libucontext_makecontext
> +#else
>  #include <ucontext.h>
> +#endif
>  #include "qemu/coroutine_int.h"

Trying on Ubuntu 20.04 I'm getting:

/usr/bin/ld: libqemuutil.a(util_coroutine-ucontext.c.o): in function
`qemu_coroutine_new':
util/coroutine-ucontext.c:203: undefined reference to
`libucontext_getcontext'
/usr/bin/ld: util/coroutine-ucontext.c:254: undefined reference to
`libucontext_swapcontext'
/usr/bin/ld: libucontext.a(libucontext_arch_x86_64_makecontext.c.o): in
function `libucontext_makecontext':
libucontext/arch/x86_64/makecontext.c:54: undefined reference to
`_start_context'
collect2: error: ld returned 1 exit status

Regards,

Phil.