gh-153400: Resolve newer libc/syscall wrappers at runtime on Linux - #154816
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daandemeyer wants to merge 1 commit into
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gh-153400: Resolve newer libc/syscall wrappers at runtime on Linux#154816daandemeyer wants to merge 1 commit into
daandemeyer wants to merge 1 commit into
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os functions like copy_file_range() are gated on a configure-time AC_CHECK_FUNCS probe and compiled out when the build libc lacks the symbol. A redistributable built against an old glibc (the python-build-standalone builds target glibc 2.17) therefore never exposes them, even when run on a newer glibc or a capable kernel. Add Modules/posixshims.h, which on Linux always exposes _Py_<func>(), resolves the libc symbol once at load time via dlsym(RTLD_DEFAULT) from a constructor, and falls back to the raw syscall when the running libc lacks the wrapper. Resolving in a constructor keeps dlsym(), which is not async-signal-safe, out of signal handlers and the fork()/exec() window. Off Linux the classic build-time HAVE_* direct calls are kept. Limit the shims to wrappers newer than the glibc 2.17 baseline, since anything at or below it is always present in the build libc: copy_file_range (glibc 2.27) memfd_create (glibc 2.27) pidfd_open (glibc 2.36) pidfd_getfd (glibc 2.36) pidfd_open() and pidfd_getfd() previously issued raw syscalls unconditionally; they now prefer the glibc wrapper when present. Signed-off-by: Daan De Meyer <daan@amutable.com>
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os functions like copy_file_range() are gated on a configure-time AC_CHECK_FUNCS probe and compiled out when the build libc lacks the symbol. A redistributable built against an old glibc (the python-build-standalone builds target glibc 2.17) therefore never exposes them, even when run on a newer glibc or a capable kernel.
Add Modules/posixshims.h, which on Linux always exposes Py(), resolves the libc symbol once at load time via dlsym(RTLD_DEFAULT) from a constructor, and falls back to the raw syscall when the running libc lacks the wrapper. Resolving in a constructor keeps dlsym(), which is not async-signal-safe, out of signal handlers and the fork()/exec() window. Off Linux the classic build-time HAVE_* direct calls are kept.
Limit the shims to wrappers newer than the glibc 2.17 baseline, since anything at or below it is always present in the build libc:
copy_file_range (glibc 2.27)
memfd_create (glibc 2.27)
pidfd_open (glibc 2.36)
pidfd_getfd (glibc 2.36)
pidfd_open() and pidfd_getfd() previously issued raw syscalls unconditionally; they now prefer the glibc wrapper when present.