[Buildroot] [PATCH v2 1/2] package/libabseil-cpp: disable for the MIPS n32 ABI

[Yegor Yefremov via buildroot <buildroot@buildroot.org>]

From: Yegor Yefremov <yegorslists@googlemail.com>

absl::base_internal::DirectMmap() only implements mmap() via mmap2 for
the o32 ABI on MIPS:

    #if ... (defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI32) || ...

With the n32 ABI, the "remaining 64-bit architectures" fallback is
selected instead, which fails to build because long is 32-bit there:

    absl/base/internal/direct_mmap.h: In function 'void* absl::lts_20260107::base_internal::DirectMmap(void*, size_t, int, int, int, off_t)':
    absl/base/internal/direct_mmap.h:130:39: error: static assertion failed: Platform is not 64-bit
      130 |   static_assert(sizeof(unsigned long) == 8, "Platform is not 64-bit");
          |                 ~~~~~~~~~~~~~~~~~~~~~~^~~~
    absl/base/internal/direct_mmap.h:130:39: note: the comparison reduces to '(4 == 8)'

direct_mmap.h is included by absl/base/internal/low_level_alloc.cc and
absl/base/internal/poison.cc, which are always built, so the failure is
unconditional. Upstream abseil has no support for the n32 ABI, so
disable the package for that ABI.

Since n32 is the default ABI for BR2_mips64/BR2_mips64el, this affects
every mips64 build that does not explicitly select n64. The o32
(BR2_MIPS_OABI32) and n64 (BR2_MIPS_NABI64) ABIs are unaffected, and all
in-tree mips64 defconfigs use n64.

For the LTS maintainers: the ABI list in direct_mmap.h is identical in
abseil 20200225 (the version in tree when the arch dependencies were
introduced) and in the current 20260817.0, so the failure has existed
ever since mips64 was allowed. It is still reproduced on all maintained
branches, e.g.:

    2026.02.x https://autobuild.buildroot.net/results/5818407a73cfd3371cd1f726a24df6ceb9afa42d/
    2025.02.x https://autobuild.buildroot.net/results/5065bda3b91bdbee53559dd97af8ab5a63a1e112/

so a backport is needed there.

Fixes: ae0557403a3a4cbf5354f0ab1784a08623382e5e ("package/libabseil-cpp: add BR2_PACKAGE_LIBABSEIL_CPP_ARCH_SUPPORTS")
Fixes:
https://autobuild.buildroot.net/results/f375584f3721d61238b9e43d9926e037802f6141/

Assisted-by: Claude:claude-opus-5
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
---
 package/libabseil-cpp/Config.in | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/package/libabseil-cpp/Config.in b/package/libabseil-cpp/Config.in
index d13bf6e663..feb4963042 100644
--- a/package/libabseil-cpp/Config.in
+++ b/package/libabseil-cpp/Config.in
@@ -14,6 +14,10 @@ config BR2_PACKAGE_LIBABSEIL_CPP_ARCH_SUPPORTS
 	default y if BR2_sparc || BR2_sparc64
 	default y if BR2_x86_64
 	depends on BR2_TOOLCHAIN_HAS_UCONTEXT
+	# absl/base/internal/direct_mmap.h only implements DirectMmap()
+	# with mmap2 for the o32 ABI on MIPS, and its 64-bit fallback
+	# fails to build with the n32 ABI, where long is 32-bit
+	depends on !BR2_MIPS_NABI32
 
 config BR2_PACKAGE_LIBABSEIL_CPP
 	bool "libabseil-cpp"
-- 
2.34.1

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