[libc-commits] [PATCH] D75802: [libc] Add sigaction

Alex Brachet via Phabricator via libc-commits libc-commits at lists.llvm.org
Sat Mar 7 02:42:53 PST 2020

abrachet created this revision.
abrachet added reviewers: sivachandra, MaskRay, PaulkaToast.
Herald added subscribers: tschuett, mgorny.
abrachet marked 3 inline comments as done.
abrachet added inline comments.

Comment at: libc/config/linux/signal.h.in:11
+#define sigaction __kernel_sigaction
 #include <linux/signal.h>
This is very not ideal, but the Linux headers expose a different `struct sigaction` than POSIX expects, it has no `sa_action` member.

Comment at: libc/spec/stdc.td:217
-        NamedType<"sigset_t">,
I moved this in this patch because I realized `sigset_t` doesn't belong here but rather posix.td, I can do this in a separate patch if reviewers want.

Comment at: libc/src/signal/linux/sigaction.cpp:20
+// the signals stack context.
+    "nop\n"
To elaborate more on why we can't use a function written in C, we need a way to guarantee that no stack allocations can be made, to my knowledge there is no attribute which satisfies this. The closest is `optimize("O1")` which we can assume wouldn't bother pushing anything but clang doesn't have this. Also see __restore_rt.s, to make this useable with gdb there are a lot of prerequisites which must be met that we cannot do in C (at least easily) unfortunately.

This is a work in progress and is very much not ready.

There are CMake problems to iron out right now, `add_entrypoint_object` cannot take more than 1 source file because `$<TARGET_OBJECTS:${target_name}_objects>` gets expanded to separate objects by a `;`. I also had a hard time just using `add_library` and using that target as a dependency, this has not worked. So for now I have x86 assembly inline in the .cpp file, although I have kept the .s file, I have not bothered to name it according to its architecture or choose an arch specific directory for it because I am just trying to get CMake to work.



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