How can operating systems add linker flags to the GCC specs?

How can operating systems add linker flags to the GCC specs?

[Sebastian Huber]

Hello,

for RTEMS we have in gcc/config/rtems.h the following LIB_SPEC:

#undef LIB_SPEC
#define LIB_SPEC "%{!qrtems:" STD_LIB_SPEC "} " \
"%{qrtems:%{!nostdlib:%{!nodefaultlibs:" \
"--start-group -lrtemsbsp -lrtemscpu -latomic -lc -lgcc --end-group} " \
"%{!qnolinkcmds:-T linkcmds%s}}}"

The intention was that a GCC command line to link an executable with

-qrtems -nodefaultlibs

still uses "-T linkcmds", however, this didn't work. I think this is due to

*link_gcc_c_sequence:
%G %{!nolibc:%L %G}

*link_command:
... %{!nostdlib:%{!r:%{!nodefaultlibs:%(link_ssp) 
%(link_gcc_c_sequence)}}} ...
%(post_link) }}}}}}

So, if nodefaultlib is present, the LIB_SPEC is not evaluated at all?

The problem is that LINK_SPEC is specialized by target. For RTEMS, we 
have to use the target definitions. In the default definition of 
LINK_COMMAND_SPEC (gcc/gcc.c) there is no define for operating system 
customization. Would it be possible to add something this?

diff --git a/gcc/config/rtems.h b/gcc/config/rtems.h
index 743161c4bac..a7cea9b1d2f 100644
--- a/gcc/config/rtems.h
+++ b/gcc/config/rtems.h
@@ -49,9 +49,9 @@

  #undef LIB_SPEC
  #define LIB_SPEC "%{!qrtems:" STD_LIB_SPEC "} " \
-"%{qrtems:%{!nostdlib:%{!nodefaultlibs:" \
-"--start-group -lrtemsbsp -lrtemscpu -latomic -lc -lgcc --end-group} " \
-"%{!qnolinkcmds:-T linkcmds%s}}}"
+"%{qrtems:--start-group -lrtemsbsp -lrtemscpu -latomic -lc -lgcc 
--end-group}"
+
+#define SYSTEM_LINK_SPEC "%{qrtems:%{!qnolinkcmds:-T linkcmds%s}}"

  #define TARGET_POSIX_IO

diff --git a/gcc/gcc.c b/gcc/gcc.c
index 7dccfadfef2..eff72cb3412 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -1107,6 +1107,11 @@ proper position among the other output files.  */
      %{%:sanitize(leak):" LIBLSAN_SPEC "}}}}"
  #endif

+/* Linker command line options defined by the operating system. */
+#ifndef SYSTEM_LINK_SPEC
+#define SYSTEM_LINK_SPEC ""
+#endif
+
  #ifndef POST_LINK_SPEC
  #define POST_LINK_SPEC ""
  #endif
@@ -1158,7 +1163,8 @@ proper position among the other output files.  */
         %:include(libgomp.spec)%(link_gomp)}\
      %{fgnu-tm:%:include(libitm.spec)%(link_itm)}\
      %(mflib) " STACK_SPLIT_SPEC "\
-    %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} " 
SANITIZER_SPEC " \
+    %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} " \
+    SANITIZER_SPEC " " SYSTEM_LINK_SPEC " \
      %{!nostdlib:%{!r:%{!nodefaultlibs:%(link_ssp) 
%(link_gcc_c_sequence)}}}\
      %{!nostdlib:%{!r:%{!nostartfiles:%E}}} %{T*}  \n%(post_link) }}}}}}"
  #endif

-- 
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Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
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Re: How can operating systems add linker flags to the GCC specs?

[Sebastian Huber]

On 22/01/2021 10:46, Sebastian Huber wrote:

> Hello,
>
> for RTEMS we have in gcc/config/rtems.h the following LIB_SPEC:
>
> #undef LIB_SPEC
> #define LIB_SPEC "%{!qrtems:" STD_LIB_SPEC "} " \
> "%{qrtems:%{!nostdlib:%{!nodefaultlibs:" \
> "--start-group -lrtemsbsp -lrtemscpu -latomic -lc -lgcc --end-group} " \
> "%{!qnolinkcmds:-T linkcmds%s}}}"
>
> The intention was that a GCC command line to link an executable with
>
> -qrtems -nodefaultlibs
>
> still uses "-T linkcmds", however, this didn't work. I think this is 
> due to
>
> *link_gcc_c_sequence:
> %G %{!nolibc:%L %G}
>
> *link_command:
> ... %{!nostdlib:%{!r:%{!nodefaultlibs:%(link_ssp) 
> %(link_gcc_c_sequence)}}} ...
> %(post_link) }}}}}}
>
> So, if nodefaultlib is present, the LIB_SPEC is not evaluated at all?
>
> The problem is that LINK_SPEC is specialized by target. For RTEMS, we 
> have to use the target definitions. In the default definition of 
> LINK_COMMAND_SPEC (gcc/gcc.c) there is no define for operating system 
> customization. Would it be possible to add something this? 

I think the STARTFILES_SPEC can be used as a workaround:

https://gcc.gnu.org/pipermail/gcc-patches/2021-January/564101.html

This avoids modifications in "gcc/gcc.c".

-- 
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax:   +49-89-18 94 741 - 08

Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/