[Buildroot] [PATCH 3/9] package/libabseil-cpp: allow building with musl

[Angelo Compagnucci <angelo.compagnucci@gmail.com>]

libabseil-cpp depends on BR2_TOOLCHAIN_HAS_UCONTEXT, which is not set
for musl, as it doesn't provide the {get,make,set}context functions.

However, absl/debugging/internal/examine_stack.cc only uses the ucontext
data structures, to get the program counter from the signal context,
and never calls those functions. musl provides those data structures,
so allow building with musl.

On 32-bit powerpc, examine_stack.cc assumes the glibc layout of
mcontext_t (uc_mcontext.uc_regs), which is different with musl, so keep
it disabled there.

examine_stack.cc was build-tested with the Bootlin musl toolchains for
aarch64, armv7, i686, x86-64, m68k, mips32el, powerpc64, powerpc64le,
riscv32, riscv64, s390x and sh4, and libabseil-cpp, re2, protobuf, grpc
and webrtc-audio-processing with the aarch64 and armv7 musl toolchains.

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
---
 package/libabseil-cpp/Config.in | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/package/libabseil-cpp/Config.in b/package/libabseil-cpp/Config.in
index aba065fca7..ea037f5de2 100644
--- a/package/libabseil-cpp/Config.in
+++ b/package/libabseil-cpp/Config.in
@@ -13,7 +13,11 @@ config BR2_PACKAGE_LIBABSEIL_CPP_ARCH_SUPPORTS
 	default y if BR2_sh
 	default y if BR2_sparc || BR2_sparc64
 	default y if BR2_x86_64
-	depends on BR2_TOOLCHAIN_HAS_UCONTEXT
+	# Only the ucontext data structures are used, not the
+	# {get,make,set}context functions, so musl is supported, except
+	# on 32-bit powerpc, where the glibc mcontext_t layout is assumed.
+	depends on BR2_TOOLCHAIN_HAS_UCONTEXT || BR2_TOOLCHAIN_USES_MUSL
+	depends on !(BR2_powerpc && BR2_TOOLCHAIN_USES_MUSL)
 	# 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
-- 
2.34.1

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