Re: Problem building libstdc++ for the avr target

[Jonathan Wakely <jwakely@redhat.com>]

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On 25/03/21 12:36 +0000, Jonathan Wakely wrote:
>On 25/03/21 10:27 +0100, Vladimir V wrote:
>>Hello.
>>
>>Recently I tried the 'freestanding' build of the libstdc++ for the avr to
>>verify that my fixes were sufficient for it as well.
>>Unfortunately, I encountered the following error:
>>../../../../libstdc++-v3/libsupc++/new_opa.cc: In function 'void*
>>__gnu_cxx::aligned_alloc(std::size_t, std::size_t)':
>>../../../../libstdc++-v3/libsupc++/new_opa.cc:97:28: error: 'malloc' was
>>not declared in this scope
>>  97 |   void* const malloc_ptr = malloc(sz + al);
>>
>>My investigation showed that in the chain of includes the stdlib.h of the
>>avr-libc is not present.
>>It looks like includes are resolved in the following way (here are the
>>original paths as they are linked from out folders during build):
>>new_opa.cc -> libstdc++-v3/include/c_compatibility/stdlib.h ->
>>libstdc++-v3/include/c_global/cstdlib
>>In cstdlib, for non-hosted builds stdlib.h is not included.
>>
>>This problem is not present if the non-hosted build is done with
>>'with-newlib' flag instead of 'with-avrlibc' (common workaround as the
>>avrlibc build was fixed only recently).
>>Might it be that some include order depends on the target libc? Or maybe
>>some implicit conditions are involved?
>>
>>Could you please support me with this issue?
>
>I think this is needed:
>
>--- a/libstdc++-v3/libsupc++/new_opa.cc
>+++ b/libstdc++-v3/libsupc++/new_opa.cc
>@@ -54,6 +54,10 @@ extern "C"
>   void *posix_memalign(void **, size_t alignment, size_t size);
> # elif _GLIBCXX_HAVE_MEMALIGN
>   void *memalign(size_t alignment, size_t size);
>+#else
>+  // A freestanding C runtime may not provide "malloc" -- but there is no
>+  // other reasonable way to implement "operator new".
>+  void *malloc (std::size_t);   with GCC 7.5

Oops, there was a stray "with GCC 7.5" that got into my clipboard
there!

I've pushed the attached patch, please test and confirm if it fixes
your problem.



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commit 15d649f79d6b6dc336f6a32eec242b652a262a82
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Mar 25 18:24:37 2021

    libstdc++: Declare malloc for freestanding
    
    For a target with none of aligned_alloc, memalign etc. we defined our
    own aligned_alloc using malloc, so we need a declaration of malloc. As
    in libsupc++/new_op.cc we need to declare it ourselves for freestanding
    environments.
    
    libstdc++-v3/ChangeLog:
    
            * libsupc++/new_opa.cc [!_GLIBCXX_HOSTED]: Declare malloc.

diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 59296226e83..6b78729dc24 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -54,6 +54,10 @@ extern "C"
   void *posix_memalign(void **, size_t alignment, size_t size);
 # elif _GLIBCXX_HAVE_MEMALIGN
   void *memalign(size_t alignment, size_t size);
+# else
+  // A freestanding C runtime may not provide "malloc" -- but there is no
+  // other reasonable way to implement "operator new".
+  void *malloc(size_t);
 # endif
 }
 #endif