Building musl-cross-make with gnat in musl environement

[Didier Kryn <kryn@in2p3.fr>]

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Le 02/11/2017 à 10:44, Didier Kryn a écrit :
>     I report the successfull build of the cross-compiler 
> x86_64-musl-gcc-6.3.0 - understanding Ada - on x86_64 Debian Wheezy.
>
>     The toolchain for build was gcc-6.3.0 for Linux-Gnu provided by 
> Adacore.The build toolchain to build major version 6 must be at least 
> major version 5.
>
>     Of course, the language option must be 
> '--enable-languages=ada,c,c++' .
>
>     Three patches were necessary:
>        gnat63-terminals.diff: removes a #include <termio.h> in a C 
> source file.
>        gnat63-prj-attr.diff: corrects the layout of a record in an Ada 
> source file to prevent a warning concerning performance.
>        gnat63-xr_tabls.diff: same as the previous. 

   In a glibc environment, x86_64-musl-gcc-6.3.0 builds without error 
with the three patches I have previously reported. To check there is no 
leak of the glibc native toolchain into the cross-compiler, I tried the 
build in a musl chroot (without any glibc headers or library), still 
with '--enable-languages=ada,c,c++'.

     In a first attempt, the compilation fails with the following error:

----------------------------------------
In file included from ../../src_toolchain/gcc/ada/adaint.h:290:0,
                  from ../../src_toolchain/gcc/ada/adadecode.c:45:
/usr/pkg/gcc-6.3/lib/gcc/x86_64-pc-linux-musl/6.3.0/../../../../x86_64-pc-linux-musl/include/sched.h:76:7: 
error: attempt to use poisoned "calloc"
  void *calloc(size_t, size_t);
        ^
/usr/pkg/gcc-6.3/lib/gcc/x86_64-pc-linux-musl/6.3.0/../../../../x86_64-pc-linux-musl/include/sched.h:116:36: 
error: attempt to use poisoned "calloc"
  #define CPU_ALLOC(n) ((cpu_set_t *)calloc(1,CPU_ALLOC_SIZE(n)))
----------------------------------------

     The Ada language has "tasking" primitives, which are nowadays based 
on POSIX threads. For this, adaint.h and other files include <sched.h> 
which, unfortunately, contains a declaration of calloc() and references 
to it. This is unfortunate because calloc() is poisoned  by gcc, to 
avoid interferences with its own allocation functions, and Gnat does 
only need a small part of sched.h.

     There must be a necessity, specific to musl, to make use of 
calloc() in sched.h, because glibc doesn't do so.

     A workaround, provided by the patch gnat63-adaint.diff, is to 
replace #include <sched.h> with the few lines of this file actually 
needed in adaint.h. The patch contains also #define _SCHED_H, which is 
necessary to prevent the inclusion of sched.h by other files, directly 
or indirectly.

     With this additional patch,  x86_64-musl-gcc-6.3.0 builds without 
error both in a glibc environement and in a musl environment.

     Didier


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--- gcc-6.3.0-A/gcc/ada/adaint.c
+++ gcc-6.3.0-B/gcc/ada/adaint.c
@@ -3086,7 +3086,7 @@
 #endif
 
 #if defined (__linux__)
-#include <sched.h>
+/* do not #include <sched.h> */
 
 /* glibc versions earlier than 2.7 do not define the routines to handle
    dynamically allocated CPU sets. For these targets, we use the static
--- gcc-6.3.0-A/gcc/ada/adaint.h
+++ gcc-6.3.0-B/gcc/ada/adaint.h
@@ -287,7 +287,17 @@
 
 /* Routines for interface to required CPU set primitives */
 
-#include <sched.h>
+/* Do not #include <sched.h>, but copy part of it and prevent its inclusion */
+# ifndef _SCHED_H
+# define _SCHED_H
+typedef struct cpu_set_t { unsigned long __bits[128/sizeof(long)]; } cpu_set_t;
+# define CPU_ZERO_S(size,set) memset(set,0,size)
+# define CPU_ZERO(set) CPU_ZERO_S(sizeof(cpu_set_t),set)
+# define __CPU_op_S(i, size, set, op) ( (i)/8U >= (size) ? 0 : \                 
+        (((unsigned long *)(set))[(i)/8/sizeof(long)] op (1UL<<((i)%(8*sizeof(long))))) )
+# define CPU_SET_S(i, size, set) __CPU_op_S(i, size, set, |=)
+# define CPU_SET(i, set) CPU_SET_S(i,sizeof(cpu_set_t),set)
+# endif
 
 extern cpu_set_t *__gnat_cpu_alloc                 (size_t);
 extern size_t __gnat_cpu_alloc_size                (size_t);