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Return address signing requires unwinder support, which is present in libgcc since >=gcc-7, however due to bugs the support may be broken in <gcc-10 (and similarly there may be issues in custom unwinders), so pac-ret is not always safe to use. So in assembly code glibc should only use pac-ret if the compiler uses it too. Unfortunately there is no predefined feature macro for it set by the compiler so pac-ret is inferred from the code generation. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
64 lines
2.4 KiB
Plaintext
64 lines
2.4 KiB
Plaintext
GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
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# Local configure fragment for sysdeps/aarch64.
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# We check to see if the compiler and flags are
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# selecting the big endian ABI and if they are then
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# we set libc_cv_aarch64_be to yes which causes
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# HAVE_AARCH64_BE to be defined in config.h and
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# in include/libc-symbols.h and thus available to
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# shlib-versions to select the appropriate name for
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# the dynamic linker via %ifdef.
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AC_CACHE_CHECK([for big endian],
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[libc_cv_aarch64_be],
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[AC_EGREP_CPP(yes,[#ifdef __AARCH64EB__
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yes
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#endif
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], libc_cv_aarch64_be=yes, libc_cv_aarch64_be=no)])
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if test $libc_cv_aarch64_be = yes; then
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AC_DEFINE(HAVE_AARCH64_BE)
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LIBC_CONFIG_VAR([default-abi], [lp64_be])
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else
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LIBC_CONFIG_VAR([default-abi], [lp64])
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fi
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# Only consider BTI supported if -mbranch-protection=bti is
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# on by default in the compiler and the linker produces
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# binaries with GNU property notes in PT_GNU_PROPERTY segment.
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AC_CACHE_CHECK([for BTI support], [libc_cv_aarch64_bti], [dnl
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cat > conftest.c <<EOF
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void foo (void) { }
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EOF
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libc_cv_aarch64_bti=no
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if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -nostdlib -nostartfiles $no_ssp -shared -fPIC -o conftest.so conftest.c]) \
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&& AC_TRY_COMMAND([$READELF -lW conftest.so | grep -q GNU_PROPERTY]) \
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&& AC_TRY_COMMAND([$READELF -nW conftest.so | grep -q "NT_GNU_PROPERTY_TYPE_0.*AArch64 feature:.* BTI"])
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then
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libc_cv_aarch64_bti=yes
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fi
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rm -rf conftest.*])
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LIBC_CONFIG_VAR([aarch64-bti], [$libc_cv_aarch64_bti])
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if test $libc_cv_aarch64_bti = yes; then
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AC_DEFINE(HAVE_AARCH64_BTI)
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fi
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# Check if glibc is built with return address signing, i.e.
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# if -mbranch-protection=pac-ret is on. We need this because
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# pac-ret relies on unwinder support so it's not safe to use
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# it in assembly code unconditionally, but there is no
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# feature test macro for it in gcc.
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AC_CACHE_CHECK([if pac-ret is enabled], [libc_cv_aarch64_pac_ret], [dnl
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cat > conftest.c <<EOF
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int bar (void);
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int foo (void) { return bar () + 1; }
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EOF
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libc_cv_aarch64_pac_ret=no
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if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS -S -o conftest.s conftest.c]) \
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&& AC_TRY_COMMAND([grep -q -E '\''(hint( | )+25|paciasp)'\'' conftest.s])
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then
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libc_cv_aarch64_pac_ret=yes
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fi
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rm -rf conftest.*])
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if test $libc_cv_aarch64_pac_ret = yes; then
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AC_DEFINE(HAVE_AARCH64_PAC_RET)
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fi
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