Commit fc683cb01 ("compel: shstk: save CET state when CPU supports it")
started using PTRACE_ARCH_PRCTL to query shadow stack status. While
PTRACE_ARCH_PRCTL has existed in the kernel for a long time, it was only
added to glibc in version 2.27. Amazon Linux 2 (AL2) has glibc 2.26,
which does not have this definition. As a result, build on AL2 fails
with the below error:
compel/arch/x86/src/lib/infect.c: In function ‘get_task_xsave’:
compel/arch/x86/src/lib/infect.c:276:14: error: ‘PTRACE_ARCH_PRCTL’ undeclared (first use in this function)
276 | if (ptrace(PTRACE_ARCH_PRCTL, pid, (unsigned long)&features, ARCH_SHSTK_STATUS)) {
| ^~~~~~~~~~~~~~~~~
While the definition is present on the system via the kernel headers (in
asm/ptrace-abi.h) which can be reached by including linux/ptrace.h, the
comment in compel/include/uapi/ptrace.h says:
We'd want to include both sys/ptrace.h and linux/ptrace.h, hoping
that most definitions come from either one or another. Alas, on
Alpine/musl both files declare struct ptrace_peeksiginfo_args, so
there is no way they can be used together. Let's rely on libc one.
Since including linux/ptrace.h is not an option, define
PTRACE_ARCH_PRCTL if it doesn't already exist. An interesting point to
note is that in sys/ptrace.h, PTRACE_ARCH_PRCTL is an enum value so the
preprocessor doesn't know about it. PT_ARCH_PRCTL is the preprocessor
symbol that matches the value of PTRACE_ARCH_PRCTL. So look for
PT_ARCH_PRCTL to decide if PTRACE_ARCH_PRCTL is available or not.
Another interesting point to note is that AL2 ships with GCC 7 by
default, which does not support the -mshstk option, causing other build
failures. Luckily, it also ships GCC 10 which does have the option.
Using GCC 10 lets the build succeed.
Fixes: fc683cb01 ("compel: shstk: save CET state when CPU supports it")
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
ca971b7f8b